Drareg
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The link below offers some additional info on this enzyme.
Description
The HSD11B2 gene encodes the type II isoform of 11-beta-hydroxysteroid dehydrogenase, a microsomal enzyme complex responsible for the interconversion of biologically active cortisol and inactive cortisone. The type I isoform, encoded by the HSD11B1 gene (600713) on chromosome 1q, has 2 separate enzymatic activities: 11-beta-dehydrogenase (cortisol to cortisone) and 11-oxoreductase (cortisone to cortisol) (Lakshmi and Monder, 1985). The type II isoform (HSD11B2) only catalyzes the cortisol-to-cortisone reaction. Whereas the type I isoform is ubiquitous, the type II isoform has more restricted expression, particularly in the kidney and placenta (review by Ferrari, 2010).
Cloning and Expression
Albiston et al. (1994) cloned HSD11B2 and showed that it shared 35% sequence identity with 17-beta-hydroxysteroid dehydrogenase-2 (HSD17B2; 109685) but only 14% identity with HSD11B1. The HSD11B2 was highly expressed in kidney, colon, pancreas and placenta; the message was also present in ovary, prostate and testis. This isoform was found to be NAD(+)-dependent, exclusively dehydrogenase in directionality, inhibited by glycyrrhetinic acid, and able to metabolize the synthetic glucocorticoid dexamethasone. Albiston et al. (1994) concluded that the enzyme likely protects the nonselective mineralocorticoid receptor from occupation by glucocorticoids, and modulates access of glucocorticoids to glucocorticoid receptors, resulting in protection of the fetus and gonads.
Agarwal et al. (1995) also cloned the HSD11B2 gene, which they designated HSD11K. The nucleotide-binding domain lies in the first and second exons, and the catalytic domain in the fourth exon. The 5-prime flanking sequences and the first exon are GC-rich (80%), suggesting to the authors that the gene may be transcriptionally regulated by factors that recognize GC-rich sequences. In contrast, the HSD11L or liver isozyme (HSD11B1) is encoded by a gene with 6 exons. The coding sequences of HSD11K and HSD11L were only 21% identical. In vitro, the NAD(+)-dependent kidney (type 2) isozyme catalyzes 11-beta-dehydrogenase but not reductase reactions, whereas the NADP(+)-dependent liver isozyme catalyzes both reactions. Agarwal et al. (1995) noted that HSD11K is expressed at high levels in the placenta and kidney of midgestation human fetuses and at lower levels in lung and testes. Different transcriptional start sites are used in kidney and placenta.
Gene Structure
Agarwal et al. (1995) determined that the HSD11B2 gene contains of 5 exons and has a total length of about 6.2 kb.
Agarwal and White (2000) identified the ATP6V0D1 gene (607028) on the complementary strand of DNA encoding HSD11B2 and determined that their 3-prime ends are only 0.5 kb apart.
Nawrocki et al. (2002) determined that the HSD11B2 promoter lacks a TATA-like element but contains several putative SP1 (189906)-binding sites. Both SP1 and SP3 (601804) bound to oligonucleotides containing the putative regulatory elements.
Mapping
By fluorescence in situ hybridization (FISH), Agarwal et al. (1995)localized the HSD11B2 gene to chromosome 16q22. By FISH and use of an HSD11B2 cDNA isolated from human kidney as probe, Krozowski et al. (1995) confirmed the assignment to 16q22.
Gene Function
Funder et al. (1988) determined that target tissue specificity in mineralocorticoid action is mediated by an enzyme, not the receptor. In vitro, the mineralocorticoid receptor (MR, NR3C2; 600983) is nonspecific and does not distinguish between aldosterone and cortisol. In vivo, however, certain tissues with this receptor are aldosterone selective (e.g., kidney and parotid), whereas others with the same receptor are not (e.g., hippocampus and heart). The dehydrogenase activity of HSD11B2, which converts the active cortisol to inactive cortisone, is thought to be necessary to protect the renal mineralocorticoid receptor from normally higher serum concentrations of cortisol, allowing aldosterone to regulate sodium homeostasis (Funder et al., 1988).
In rats, the 11-beta-hydroxysteroid dehydrogenase (which converts cortisol to cortisone in man and corticosterone to 11-dehydrocorticosterone in the rat) is much more highly concentrated in aldosterone-selective tissues than in nonselective tissues. Edwards et al. (1988) suggested that the localization in the selective tissues is such that the enzyme can act as a paracrine or possibly an autocrine protector of the receptor from exposure to corticosterone. Patients with congenital deficiency of 11-beta-HSD type II (218030) and those in whom the enzyme has been inhibited by licorice (glycyrrhetinic acid) lose this protection and develop sodium retention, hypokalemia, and hypertension.
HSD11B2 confers specificity on the mineralocorticoid receptor by converting biologically active glucocorticoids to inactive metabolites. Placental HSD11B2 is also thought to protect the fetus from high levels of circulating maternal glucocorticoid. Hirasawa et al. (2000) examined the immunoreactivity of HSD11B2 and MR in human placenta from 5 weeks' gestation to full term using immunohistochemistry, HSD11B2 mRNA expression using Northern blot analysis, and MR mRNA expression using RT-PCR analysis. Marked HSD11B2 immunoreactivity was detected in placental syncytiotrophoblasts at all gestational stages. MR immunoreactivity was moderately detected in syncytiotrophoblasts, some cytotrophoblasts, and interstitial cells of the villous core. The results suggested that placental HSD11B2 is involved not only in regulating the passage of maternal active glucocorticoids into the fetal circulation but also in regulation of maternal-fetal electrolyte and water transport in the placenta, as in other mineralocorticoid target organs.
HSD11B1 and HSD11B2 expression within the anterior pituitary gland may modulate glucocorticoid feedback at an autocrine level. Korbonits et al. (2001) speculated that this may be deranged in Cushing disease (219090). HSD11B1 and HSD11B2 immunoreactive protein was detected using fluorescence immunohistochemistry. In normal pituitary, positive staining for HSD11B1-immunoreactive protein was observed in GH (139250)- and PRL (176760)-secreting cells and in folliculo-stellate cells; gonadotrophs, thyrotrophs, and ACTH-positive cells were negative. HSD11B2 immunoreactivity was absent in all cell types. RT-PCR detected HSD11B1 mRNA expression in the normal pituitary; HSD11B2 mRNA expression was also detected in most normal tissues. By contrast, in ACTH-secreting adenomas HSD11B2 immunostaining was strongly positive in every case of corticotroph adenoma. HSD11B1 immunoreactivity was also observed occasionally, but to a much lesser extent. The authors concluded that expression of HSD11B1, which generates cortisol from cortisone, in somatotrophs and lactotrophs suggests an autocrine role for this isoenzyme in the glucocorticoid regulation of pituitary GH and PRL secretion. They also concluded that HSD11B2 expression is markedly induced in ACTH-secreting pituitary tumors and, by converting cortisol to cortisone, may explain the resetting of glucocorticoid feedback control in Cushing disease.
Murphy et al. (2002) questioned whether there are alterations in placental HSD11B2 in pregnancies complicated by asthma (600807). They measured placental HSD11B2 activity, protein and mRNA, and placental corticotropin-releasing hormone (CRH; 122560) mRNA in pregnant asthmatic and nonasthmatic control women, and fetal cortisol and fetal estriol concentrations at delivery. There was a 25% reduction in neonatal birth weight centile in asthmatic women who did not use inhaled glucocorticoid treatment. This was accompanied by significantly reduced placental HSD11B2 activity, significantly increased fetal cortisol, and a trend toward increased placental CRH mRNA and reduced fetal estriol concentrations. The use of inhaled glucocorticoids for treatment was associated with birth weight centile, HSD11B2 activity, CRH mRNA, fetal cortisol, and estriol concentrations similar to control levels. The authors concluded that HSD11B2 activity is significantly reduced in asthmatic women who do not take inhaled glucocorticoids for asthma treatment, suggesting that inflammatory factors associated with asthma may be detrimental to fetal growth and development in these pregnancies.
Atanasov et al. (2007) identified a cluster of amino acids (335 to 339) in the C terminus of HSD11B2 that are essential for protein stability.
Glycyrrhizic, found in licorice, is a potent inhibitor of the HSD11B2 enzyme, and licorice consumption can sometimes cause hypertension (review by Ferrari, 2010).
Possible Role in Hypertension
Inglis et al. (1999) examined basal- and ACTH-stimulated plasma steroid levels and 24-hour corticosteroid metabolite excretion rates in 146 pairs of adult twins (75 monozygotic (MZ); 71 dizygotic (DZ)). Intraclass correlation coefficients were measured for all variables; several plasma steroid measurements were strongly related in both MZ and DZ twins, consistent with a familial pattern. These included basal levels of 11-deoxycortisol and aldosterone. ACTH-stimulated plasma aldosterone levels were also significantly correlated, to a significant degree, in both MZ and DZ twins. The index of 11-beta-hydroxysteroid dehydrogenase activity (tetrahydrocortisol + allotetrahydrocortisol/tetrahydrocortisone) and of the more specific index of activity of the type 2 isoform of this enzyme (urine free cortisol/cortisone) also correlated, to a similar degree, in DZ and MZ twins. In contrast, for the basal- and ACTH-stimulated plasma concentrations and 24-hour urine excretion rates of several corticosteroids, there was evidence of significant heritability (H2), in that correlation in MZ twins was greater than in DZ twins. The authors stated that their data provided the first evidence that plasma and urine levels of important glucocorticoids and mineralocorticoids show a strong familial pattern, and in some instances, there is evidence of a genetic component. They concluded that this suggests that corticosteroids have a plausible role in essential hypertension that has a similar heritable component.
Mune et al. (1995) raised the possibility that mild 11-beta-HSD deficiency may predispose to low birth weight and increased risk for developing hypertension.
Although progesterone reaches up to 100 times higher plasma levels in late pregnancy than aldosterone, the in vivo mineralocorticoid antagonistic effect of progesterone seems to be relatively weak. One explanation for this phenomenon could be local metabolism of progesterone in the human kidney, similar to the inactivation of cortisol to cortisone by HSD11B2. Using human kidney cortex microsomes, Quinkler et al. (1999) tested the inhibitory potency of progesterone and its metabolites on HSD11B2. The most potent inhibitor was progesterone itself. The authors concluded that inhibition of HSD11B2 leads to an increase of intracellular cortisol in such a way that the local equilibrium between the mineralocorticoid agonist cortisol and the antagonist progesterone is shifted to the agonist side, suggesting a role in preeclampsia.
Schoof et al. (2001) investigated a possible correlation between HSD11B2, converting cortisol to cortisone, and the PG-inactivating enzyme 15-hydroxyprostaglandin dehydrogenase (PGDH; 601688) gene expression in the placenta of patients with preeclampsia (see 189800). When comparing matched pairs, there were 3-fold lower HSD11B2/glyceraldehyde-3-phosphate dehydrogenase (GAPDH; 138400) mRNA levels in placentas of patients with preeclampsia than in controls. They also found a 2-fold reduction in placental PGDH/GAPDH mRNA concentrations. PGDH and HSD11B2 mRNA levels correlated significantly. In term placenta, HSD11B2/GAPDH, but not PGDH, showed a significant correlation to birth weight and to placental weight. The authors concluded that, in preeclampsia, HSD11B2 mRNA expression is reduced, leading to a decrease of HSD11B2 activity. Furthermore, by means of an autocrine or paracrine mechanism, the diminished conversion of placental cortisol may lead to reduced PGDH mRNA expression.
Heilmann et al. (2001) evaluated the activity of renal 11-beta-HSD in patients with pregnancy-induced hypertension. They measured urinary free cortisol and cortisone in patients with and without pregnancy-induced hypertension and calculated the urinary free cortisol to free cortisone ratio, which is well accepted as a correlate of the activity of renal 11-beta-HSD. The free cortisol to free cortisone ratio was significantly higher in the group with pregnancy-induced hypertension (0.47 +/- 0.25 vs 0.31 +/- 0.12, p less than 0.00002). Within this group, the patients with blood pressure in the uppermost quartile had a significantly higher free cortisol to free cortisone ratio than those in the lowest quartile. The authors concluded that a reduction of the activity of 11-beta-HSD is a relevant factor for the development of pregnancy-induced hypertension. Whether the ratio of urinary free cortisol to free cortisone is a useful risk factor for the development of pregnancy-induced hypertension remained to be investigated.
Molecular Genetics
11-Beta-Ketoreductase Deficiency Causing Apparent Mineralocorticoid Excess
In 9 patients from 8 families with apparent mineralocorticoid excess (AME; 218030) and hypertension, Mune et al. (1995)identified 7 different mutations in the HSD11B2 gene (see, e.g., 614232.0001 and 614232.0002). All patients were homozygous or compound heterozygous for the mutations. In vitro functional expression studies showed that the mutant enzymes had decreased or undetectable enzyme activity compared to controls.
In affected members of a large consanguineous Sardinian pedigree with AME, Li et al. (1998) found a homozygous mutation in the HSD11B2 gene (R279C; 218030.0006). Expression of the HSD11B2 mutant cDNA resulted in an enzyme with reduced maximum velocity, but similar substrate affinity, compared with activity of the wildtype cDNA.
Odermatt et al. (2001) provided evidence for a role of glutamic acid-115 in determining cofactor-binding specificity of HSD11B2, emphasizing the importance of structure-function analysis to elucidate the molecular mechanism of apparent mineralocorticoid excess.
In the patient reported by Werder et al. (1974), Atanasov et al. (2007) identified compound heterozygosity for 2 mutations in the HSD11B2 gene (614232.0011 and 614232.0012).
Possible Role in Hypertension
Salt-sensitive (SS) subjects increase their blood pressure with increasing salt intake. Because steroid hormones modulate renal sodium retention, Lovati et al. (1999) hypothesized that the activity of the HSD11B2 enzyme is impaired in SS subjects as compared with salt-resistant (SR) subjects. The HSD11B2 enzyme inactivates 11-hydroxysteroids in the kidney, thus protecting the nonselective mineralocorticoid receptor from occupation by glucocorticoids. Lovati et al. (1999) performed an association study using a single AluI polymorphism in exon 3 and a polymorphic microsatellite marker of the HSD11B2 gene in 149 normotensive white males (37 SS and 112 SR). The activity of the HSD11B2 enzyme was assessed by determining the urinary ratio of cortisol (THF + 5-alpha-THF) to cortisone (THE) metabolites by gas chromatography in all 37 SS subjects and in 37 age- and body habitus-matched SR volunteers. Mean cortisol-to-cortisone ratio was markedly elevated in SS subjects compared with SR subjects, indicating enhanced access of glucocorticoids to the mineralocorticoid receptor in SS subjects. In 58% of SS subjects this ratio was higher than the maximum levels in SR subjects. The salt-induced elevation in arterial pressure increased with increasing cortisol-to-cortisone ratio. A total of 12 alleles of the polymorphic microsatellite marker were detected. Homozygosity for allele A7 was higher in SS subjects than in SR subjects (41% vs 28%, p less than 0.005), whereas the occurrence of allele A7 with allele A8 was lower in SS subjects than in SR subjects (8% vs 15%, p less than 0.03). The prevalence of salt sensitivity was 35% in subjects with allele A7/A7, whereas salt sensitivity was present in only 9% of the subjects with allele A7/A8. The cortisol-to-cortisone ratio was higher in subjects homozygous for the A7 microsatellite allele as compared with the corresponding control subjects. The authors concluded that decreased HSD11B2 activity in SS subjects indicates that this enzyme is involved in salt-sensitive blood pressure response in humans, and that the association of a polymorphic microsatellite marker of the gene with a reduced HSD11B2 activity suggests that variants of the HSD11B2 gene contribute to enhanced blood pressure response to salt in humans.
Genotype/Phenotype Correlations
Nunez et al. (1999) identified 4 novel and 3 previously reported HSD11B2 mutations in 4 patients with AME. Transfection experiments showed that 2 of the mutations abolished activity in whole cells, but that 3 others retained significant activity. In regression analyses of all AME patients with published genotypes, several biochemical and clinical parameters were highly correlated with mutant enzymatic activity, which was demonstrated in whole cells, with cortisol as the substrate. The parameters included the ratio of urinary cortisone to cortisol metabolites, age at presentation, and birth weight. Approximately 5% conversion of cortisol to cortisone was predicted in subjects with mutations that completely inactivate HSD11B2, suggesting that a low level of enzymatic activity is mediated by another enzyme, possibly HSD11B1.
In a review, Ferrari (2010) noted that patients with HSD11B2 mutations showed varying degrees of severity in terms of clinical and biochemical features, according to the residual in vivo activity of the mutant enzyme. Mutations can cause a spectrum of disease, ranging from life-threatening disease in early childhood to a milder form diagnosed only in adults as isolated hypertension.
Animal Model
Kotelevtsev et al. (1999) generated Hsd11b2-null mice. All of the mice appeared normal at birth, but about 50% showed motor weakness and died within 48 hours. Male and female survivors were fertile but exhibited hypokalemia, hypotonic polyuria, and apparent mineralocorticoid activity of corticosterone. Young adult Hsd11b2-null mice were markedly hypertensive with hypertrophy and hyperplasia of the epithelium of the distal tubules of the nephron; the histologic changes did not reverse with mineralocorticoid receptor antagonism. Kotelevtsev et al. (1999) concluded that Hsd11b2-null mice provide a model for the human syndrome of apparent mineralocorticoid excess.
To evaluate aldosterone activation of cardiomyocyte mineralocorticoid receptors, Qin et al. (2003) generated transgenic mice overexpressing Hsd11b2 in cardiomyocytes, thus reducing myocardial intracellular glucocorticoids and allowing aldosterone occupancy of cardiomyocyte mineralocorticoid receptors. Transgenic mice were normotensive but spontaneously developed cardiac hypertrophy, fibrosis, and heart failure, and died prematurely on a normal salt diet. Eplerenone, a selective aldosterone blocker, ameliorated this phenotype. Qin et al. (2003)concluded that these data confirmed the deleterious consequences of inappropriate activation of cardiomyocyte mineralocorticoid receptors by aldosterone and revealed a tonic inhibitory role of glucocorticoids in preventing such outcomes under physiologic conditions.
ALLELIC VARIANTS (13 Selected Examples):
Table View ClinVar
.0001 APPARENT MINERALOCORTICOID EXCESS
HSD11B2, ARG208CYS [dbSNP:rs121917780] [ClinVar]
In a 9-year-old Native American male with apparent mineralocorticoid excess (AME; 218030) and a blood pressure of 170/100, Mune et al. (1995) identified a homozygous C-to-T transition in the HSD11B gene, resulting in an arg208-to-cys (R208C) substitution.
.0002 APPARENT MINERALOCORTICOID EXCESS
HSD11B2, ARG213CYS [dbSNP:rs28934591] [ClinVar]
In 2 children of Caucasian/Native South American ancestry with apparent mineralocorticoid excess (AME; 218030), previously reported by Shackleton et al. (1985), Mune et al. (1995) found homozygosity for a C-to-T transition in the HSD11B gene, resulting in an arg213-to-cys (R213C) substitution.
In a patient with AME, Rogoff et al. (1998) described the R213C mutation in the 11-beta-HSD2 enzyme. In vitro expression studies of the mutant construct indicated that the mutant protein is normally expressed, but that its activity is abolished. The CGC-to-TGC transition at codon 213 is at a CpG dinucleotide. Because of the occurrence of an R213C mutation in several unrelated families, the authors concluded that codon 213 is a hotspot for mutations.
.0003 APPARENT MINERALOCORTICOID EXCESS
HSD11B2, ARG337CYS [dbSNP:rs121917781] [ClinVar]
In sibs with apparent mineralocorticoid excess (AME; 218030), Wilson et al. (1995) identified a homozygous C-to-T transition in the HSD11B2 gene, resulting in an arg337-to-cys (R337C) substitution. Obeyesekere et al. (1995) examined the metabolism of cortisol in mammalian cells transfected with plasmids expressing the wildtype and mutant enzymes. In whole cells the Km of the normal enzyme was 110 nM, while the enzyme containing the R337C mutation displayed a Km of 1,010 nM. The mutant enzyme was totally inactive in cell-free preparations, suggesting that it has additional properties that may compromise its activity in whole cells.
.0004 APPARENT MINERALOCORTICOID EXCESS
HSD11B2, ARG208HIS [dbSNP:rs28934592] [ClinVar]
In a Japanese patient with apparent mineralocorticoid excess (AME; 218030), Kitanaka et al. (1997) identified compound heterozygous mutations in the HSD11B2 gene: a G-to-A transition in exon 3 resulting in an arg208-to-his (R208H) substitution, and a 3-bp deletion in exon 5 (CGCTAT to CAT) resulting in an arg-to-his substitution (R337H) and deletion of a tyr residue (del338). The latter mutation was shown to abolish HSD11B2 enzymatic activity.
.0005 APPARENT MINERALOCORTICOID EXCESS
HSD11B2, ARG337HIS [dbSNP:rs397509434] [dbSNP:rs28934593] [ClinVar]
For discussion of the arg337-to-his (R337H) mutation in the HSD11B2 gene that was found in compound heterozygous state in a patient with apparent mineralocorticoid excess (AME; 218030) by Kitanaka et al. (1997), see 614232.0004.
.0006 APPARENT MINERALOCORTICOID EXCESS
HSD11B2, ARG279CYS [dbSNP:rs28934594] [ClinVar]
In affected members of a large Sardinian family with apparent mineralocorticoid excess (AME; 218030), Li et al. (1998) identified a homozygous 945C-T transition in the HSD11B2 gene, resulting in an arg279-to-cys (R279C) substitution. Expression of the mutant cDNA resulted in an enzyme with reduced maximum velocity, but similar substrate affinity, compared with activity of the wildtype cDNA. Affected individuals were more than 30 years of age and had both mineralocorticoid hypertension and evidence of impaired metabolism of cortisol to cortisone. The heterozygous state was phenotypically normal but was associated with subtle defects in cortisol metabolism. Although the family had been considered to have 'type II' AME due to a normal urinary cortisol:corticosterone metabolite ratio, Li et al. (1998)concluded that their molecular studies demonstrated that the classification of AME into subtypes is inappropriate because AME represents a spectrum of mineralocorticoid hypertension with severity reflecting the underlying genetic defect in the HSD11B2 gene.
.0007 APPARENT MINERALOCORTICOID EXCESS, MILD
HSD11B2, PRO227LEU [dbSNP:rs121917782] [ClinVar]
In a female patient from a consanguineous Mennonite family with a mild form of apparent mineralocorticoid excess (AME; 218030), Wilson et al. (1998) identified a homozygous C-to-T transition in the HSD11B2 gene, resulting in a pro227-to-leu (P227L) substitution. She had low-renin hypertension but did not demonstrate the typical features of AME. Biochemical analysis revealed a moderately elevated cortisol-to-cortisone metabolite ratio. The conversion of cortisol to cortisone was 58% compared to 0 to 6% in patients with typical AME (the normal conversion is 90-95%). The parents and sibs were heterozygous for this mutation. Because approximately 40% of patients with essential hypertension demonstrate low renin, Wilson et al. (1998)suggested that such patients should undergo genetic analysis of the HSD11B2 gene.
In an extensive review of steroid disorders in children, specifically congenital adrenal hyperplasia and apparent mineralocorticoid excess, New and Wilson (1999) provided further information concerning what they alleged was the first reported patient with a mild form of AME. Asymptomatic hypertension was diagnosed at age 12.5 years during a sports physical. The parents were consanguineous Mennonites of Prussian descent (Alexanderwohl Church). The only family member with hypertension was the maternal grandmother. Although the patient lacked hypokalemia and low birthweight and had only mild hypertension, New and Wilson (1999) established a diagnosis for AME genetically.
.0008 APPARENT MINERALOCORTICOID EXCESS, MILD
HSD11B2, 6-BP DEL, LEU114/GLU115 [dbSNP:rs794726669] [ClinVar]
Odermatt et al. (2001) reported 2 sibs, aged 1 and 2 years, who were diagnosed with hypokalemic hypertension and low plasma aldosterone and renin levels, indicating mineralocorticoid hypertension (AME; 218030). Analysis of urinary steroid metabolites showed a markedly impaired metabolism of cortisol and nearly absent urinary free cortisone. Although phenotypically normal, the heterozygous parents showed a disturbed cortisol metabolism. Genetic analysis of the HSD11B2 gene from the AME patients revealed the homozygous deletion of 6 nucleotides in exon 2, with the resultant loss of amino acids leu114 and glu115, representing the first alteration found in the cofactor-binding domain. The deletion mutant, expressed in HEK293 cells, showed an approximately 20-fold lower maximum velocity but increased apparent affinity for cortisol and corticosterone. Functional analysis of wildtype and mutant proteins indicated that a disturbed conformation of the cofactor-binding domain, but not the missing negative charge of glu115, led to the observed decreased activity of the deletion mutant. The authors concluded that their findings provided evidence for a role of glu115 in determining cofactor-binding specificity of HSD11B2 and emphasized the importance of structure-function analysis to elucidate the molecular mechanism of apparent mineralocorticoid excess.
.0009 APPARENT MINERALOCORTICOID EXCESS
HSD11B2, ASP223ASN [dbSNP:rs121917833] [ClinVar]
In a 4-year-old male with apparent mineralocorticoid excess (AME; 218030) and arterial hypertension, Carvajal et al. (2003)detected 2 homozygous mutations in the HSD11B2 gene, a G-to-A transition in exon 4 resulting in an asp223-to-asn substitution (D223N) and a C-to-T substitution in intron 3 (7279C-T; 614232.0011). The patient's plasma renin activity and serum aldosterone were undetectable in the presence of a high cortisol-to-cortisone ratio. The mutant enzyme had only 6% of wildtype activity in transfected Chinese hamster ovary (CHO) cells. In silico 3D modeling showed that D223N changed the enzyme's surface electrostatic potential affecting the cofactor and substrate enzyme-binding capacity. Mune et al. (1995) had described the 7279C-T transition (IVS3+14C-T) and predicted it to alter the normal splicing of pre-mRNA, given a nonfunctional protein. Thus, if some mutated RNA were translated, it would carry the D223N mutation that almost abolishes enzymatic activity. Carvajal et al. (2003) concluded that these findings may determine the full inactivation of this enzyme, explaining the biochemical profile and the early onset of hypertension seen in this patient.
.0010 APPARENT MINERALOCORTICOID EXCESS
HSD11B2, TYR299DEL [dbSNP:rs794726670] [ClinVar]
In an 11-year-old Pakistani girl, born of consanguineous parents, with apparent mineralocorticoid excess (AME; 218030), Lin-Su et al. (2004) found homozygous deletion of the tyr299 (Y299) codon in exon 5 of the HSD11B2 gene. The patient presented at age 9 years with hypertension (225/120 mm Hg), low plasma renin activity, hypokalemic metabolic alkalosis, suppressed aldosterone, and bilateral nephrocalcinosis. She had had a low birth weight compared with her sibs. Biochemical analysis showed an elevated urinary cortisol-to-cortisone metabolites ratio (tetrahydrocortisol and 5-alpha-tetrahydrocortisol/tetrahydrocortisone) of 28 (normal, 0.66-2.44). She had a cortisol secretion rate of 0.43 mg/d (normal, 5-25 mg/d). In vitro expression in CHO cells revealed that this mutation resulted in no activity.
.0011 APPARENT MINERALOCORTICOID EXCESS
HSD11B2, IVS3DS, C-T, +14
In a 26-year-old Mexican American woman with apparent mineralocorticoid excess (AME; 218030), Mune et al. (1995)identified a homozygous splice site mutation in the HSD11B2 gene (IVS3+14C-T).
.0012 APPARENT MINERALOCORTICOID EXCESS
HSD11B2, TYR338HIS [dbSNP:rs387907117] [ClinVar]
In a woman with apparent mineralocorticoid excess (AME; 218030), originally reported by Werder et al. (1974), Atanasov et al. (2007) identified compound heterozygosity for 2 mutations in the HSD11B2 gene: a 2-bp deletion (CA) in exon 1, resulting in premature termination (614232.0013), and a T-to-C transition in exon 5, resulting in a tyr338-to-his (Y338H) substitution. Neither mutation was found in 300 control chromosomes. In vitro functional expression studies in HEK293 cells showed reduced levels of the Y338H mutant protein (45% lower than wildtype) as well as significantly decreased activity (less than 5% of wildtype), although there was no defect in substrate affinity. Site-directed mutagenesis studies indicated that tyr338 is absolutely essential for enzyme activity and that a cluster including residues 335 to 339 is necessary for protein stability. Subcellular distribution studies showed abnormal localization of the mutant Y338H protein, suggesting misfolding and reduced protein stability. Further studies indicated proteasome-mediated degradation. There was some recovery of activity using chemical chaperones and low temperature. The findings indicated that impaired protein stability of HSD11B2 contributed to the development of hypertension in this patient.
.0013 APPARENT MINERALOCORTICOID EXCESS
HSD11B2, 2-BP DEL
For discussion of the 2-bp deletion (CA) in exon 1 of the HSD11B2 gene that was found in compound heterozygous state in a patient with apparent mineralocorticoid excess (AME; 218030) by Atanasov et al. (2007), see
OMIM Entry - * 614232 - 11-BETA-HYDROXYSTEROID DEHYDROGENASE, TYPE II; HSD11B2
Description
The HSD11B2 gene encodes the type II isoform of 11-beta-hydroxysteroid dehydrogenase, a microsomal enzyme complex responsible for the interconversion of biologically active cortisol and inactive cortisone. The type I isoform, encoded by the HSD11B1 gene (600713) on chromosome 1q, has 2 separate enzymatic activities: 11-beta-dehydrogenase (cortisol to cortisone) and 11-oxoreductase (cortisone to cortisol) (Lakshmi and Monder, 1985). The type II isoform (HSD11B2) only catalyzes the cortisol-to-cortisone reaction. Whereas the type I isoform is ubiquitous, the type II isoform has more restricted expression, particularly in the kidney and placenta (review by Ferrari, 2010).
Cloning and Expression
Albiston et al. (1994) cloned HSD11B2 and showed that it shared 35% sequence identity with 17-beta-hydroxysteroid dehydrogenase-2 (HSD17B2; 109685) but only 14% identity with HSD11B1. The HSD11B2 was highly expressed in kidney, colon, pancreas and placenta; the message was also present in ovary, prostate and testis. This isoform was found to be NAD(+)-dependent, exclusively dehydrogenase in directionality, inhibited by glycyrrhetinic acid, and able to metabolize the synthetic glucocorticoid dexamethasone. Albiston et al. (1994) concluded that the enzyme likely protects the nonselective mineralocorticoid receptor from occupation by glucocorticoids, and modulates access of glucocorticoids to glucocorticoid receptors, resulting in protection of the fetus and gonads.
Agarwal et al. (1995) also cloned the HSD11B2 gene, which they designated HSD11K. The nucleotide-binding domain lies in the first and second exons, and the catalytic domain in the fourth exon. The 5-prime flanking sequences and the first exon are GC-rich (80%), suggesting to the authors that the gene may be transcriptionally regulated by factors that recognize GC-rich sequences. In contrast, the HSD11L or liver isozyme (HSD11B1) is encoded by a gene with 6 exons. The coding sequences of HSD11K and HSD11L were only 21% identical. In vitro, the NAD(+)-dependent kidney (type 2) isozyme catalyzes 11-beta-dehydrogenase but not reductase reactions, whereas the NADP(+)-dependent liver isozyme catalyzes both reactions. Agarwal et al. (1995) noted that HSD11K is expressed at high levels in the placenta and kidney of midgestation human fetuses and at lower levels in lung and testes. Different transcriptional start sites are used in kidney and placenta.
Gene Structure
Agarwal et al. (1995) determined that the HSD11B2 gene contains of 5 exons and has a total length of about 6.2 kb.
Agarwal and White (2000) identified the ATP6V0D1 gene (607028) on the complementary strand of DNA encoding HSD11B2 and determined that their 3-prime ends are only 0.5 kb apart.
Nawrocki et al. (2002) determined that the HSD11B2 promoter lacks a TATA-like element but contains several putative SP1 (189906)-binding sites. Both SP1 and SP3 (601804) bound to oligonucleotides containing the putative regulatory elements.
Mapping
By fluorescence in situ hybridization (FISH), Agarwal et al. (1995)localized the HSD11B2 gene to chromosome 16q22. By FISH and use of an HSD11B2 cDNA isolated from human kidney as probe, Krozowski et al. (1995) confirmed the assignment to 16q22.
Gene Function
Funder et al. (1988) determined that target tissue specificity in mineralocorticoid action is mediated by an enzyme, not the receptor. In vitro, the mineralocorticoid receptor (MR, NR3C2; 600983) is nonspecific and does not distinguish between aldosterone and cortisol. In vivo, however, certain tissues with this receptor are aldosterone selective (e.g., kidney and parotid), whereas others with the same receptor are not (e.g., hippocampus and heart). The dehydrogenase activity of HSD11B2, which converts the active cortisol to inactive cortisone, is thought to be necessary to protect the renal mineralocorticoid receptor from normally higher serum concentrations of cortisol, allowing aldosterone to regulate sodium homeostasis (Funder et al., 1988).
In rats, the 11-beta-hydroxysteroid dehydrogenase (which converts cortisol to cortisone in man and corticosterone to 11-dehydrocorticosterone in the rat) is much more highly concentrated in aldosterone-selective tissues than in nonselective tissues. Edwards et al. (1988) suggested that the localization in the selective tissues is such that the enzyme can act as a paracrine or possibly an autocrine protector of the receptor from exposure to corticosterone. Patients with congenital deficiency of 11-beta-HSD type II (218030) and those in whom the enzyme has been inhibited by licorice (glycyrrhetinic acid) lose this protection and develop sodium retention, hypokalemia, and hypertension.
HSD11B2 confers specificity on the mineralocorticoid receptor by converting biologically active glucocorticoids to inactive metabolites. Placental HSD11B2 is also thought to protect the fetus from high levels of circulating maternal glucocorticoid. Hirasawa et al. (2000) examined the immunoreactivity of HSD11B2 and MR in human placenta from 5 weeks' gestation to full term using immunohistochemistry, HSD11B2 mRNA expression using Northern blot analysis, and MR mRNA expression using RT-PCR analysis. Marked HSD11B2 immunoreactivity was detected in placental syncytiotrophoblasts at all gestational stages. MR immunoreactivity was moderately detected in syncytiotrophoblasts, some cytotrophoblasts, and interstitial cells of the villous core. The results suggested that placental HSD11B2 is involved not only in regulating the passage of maternal active glucocorticoids into the fetal circulation but also in regulation of maternal-fetal electrolyte and water transport in the placenta, as in other mineralocorticoid target organs.
HSD11B1 and HSD11B2 expression within the anterior pituitary gland may modulate glucocorticoid feedback at an autocrine level. Korbonits et al. (2001) speculated that this may be deranged in Cushing disease (219090). HSD11B1 and HSD11B2 immunoreactive protein was detected using fluorescence immunohistochemistry. In normal pituitary, positive staining for HSD11B1-immunoreactive protein was observed in GH (139250)- and PRL (176760)-secreting cells and in folliculo-stellate cells; gonadotrophs, thyrotrophs, and ACTH-positive cells were negative. HSD11B2 immunoreactivity was absent in all cell types. RT-PCR detected HSD11B1 mRNA expression in the normal pituitary; HSD11B2 mRNA expression was also detected in most normal tissues. By contrast, in ACTH-secreting adenomas HSD11B2 immunostaining was strongly positive in every case of corticotroph adenoma. HSD11B1 immunoreactivity was also observed occasionally, but to a much lesser extent. The authors concluded that expression of HSD11B1, which generates cortisol from cortisone, in somatotrophs and lactotrophs suggests an autocrine role for this isoenzyme in the glucocorticoid regulation of pituitary GH and PRL secretion. They also concluded that HSD11B2 expression is markedly induced in ACTH-secreting pituitary tumors and, by converting cortisol to cortisone, may explain the resetting of glucocorticoid feedback control in Cushing disease.
Murphy et al. (2002) questioned whether there are alterations in placental HSD11B2 in pregnancies complicated by asthma (600807). They measured placental HSD11B2 activity, protein and mRNA, and placental corticotropin-releasing hormone (CRH; 122560) mRNA in pregnant asthmatic and nonasthmatic control women, and fetal cortisol and fetal estriol concentrations at delivery. There was a 25% reduction in neonatal birth weight centile in asthmatic women who did not use inhaled glucocorticoid treatment. This was accompanied by significantly reduced placental HSD11B2 activity, significantly increased fetal cortisol, and a trend toward increased placental CRH mRNA and reduced fetal estriol concentrations. The use of inhaled glucocorticoids for treatment was associated with birth weight centile, HSD11B2 activity, CRH mRNA, fetal cortisol, and estriol concentrations similar to control levels. The authors concluded that HSD11B2 activity is significantly reduced in asthmatic women who do not take inhaled glucocorticoids for asthma treatment, suggesting that inflammatory factors associated with asthma may be detrimental to fetal growth and development in these pregnancies.
Atanasov et al. (2007) identified a cluster of amino acids (335 to 339) in the C terminus of HSD11B2 that are essential for protein stability.
Glycyrrhizic, found in licorice, is a potent inhibitor of the HSD11B2 enzyme, and licorice consumption can sometimes cause hypertension (review by Ferrari, 2010).
Possible Role in Hypertension
Inglis et al. (1999) examined basal- and ACTH-stimulated plasma steroid levels and 24-hour corticosteroid metabolite excretion rates in 146 pairs of adult twins (75 monozygotic (MZ); 71 dizygotic (DZ)). Intraclass correlation coefficients were measured for all variables; several plasma steroid measurements were strongly related in both MZ and DZ twins, consistent with a familial pattern. These included basal levels of 11-deoxycortisol and aldosterone. ACTH-stimulated plasma aldosterone levels were also significantly correlated, to a significant degree, in both MZ and DZ twins. The index of 11-beta-hydroxysteroid dehydrogenase activity (tetrahydrocortisol + allotetrahydrocortisol/tetrahydrocortisone) and of the more specific index of activity of the type 2 isoform of this enzyme (urine free cortisol/cortisone) also correlated, to a similar degree, in DZ and MZ twins. In contrast, for the basal- and ACTH-stimulated plasma concentrations and 24-hour urine excretion rates of several corticosteroids, there was evidence of significant heritability (H2), in that correlation in MZ twins was greater than in DZ twins. The authors stated that their data provided the first evidence that plasma and urine levels of important glucocorticoids and mineralocorticoids show a strong familial pattern, and in some instances, there is evidence of a genetic component. They concluded that this suggests that corticosteroids have a plausible role in essential hypertension that has a similar heritable component.
Mune et al. (1995) raised the possibility that mild 11-beta-HSD deficiency may predispose to low birth weight and increased risk for developing hypertension.
Although progesterone reaches up to 100 times higher plasma levels in late pregnancy than aldosterone, the in vivo mineralocorticoid antagonistic effect of progesterone seems to be relatively weak. One explanation for this phenomenon could be local metabolism of progesterone in the human kidney, similar to the inactivation of cortisol to cortisone by HSD11B2. Using human kidney cortex microsomes, Quinkler et al. (1999) tested the inhibitory potency of progesterone and its metabolites on HSD11B2. The most potent inhibitor was progesterone itself. The authors concluded that inhibition of HSD11B2 leads to an increase of intracellular cortisol in such a way that the local equilibrium between the mineralocorticoid agonist cortisol and the antagonist progesterone is shifted to the agonist side, suggesting a role in preeclampsia.
Schoof et al. (2001) investigated a possible correlation between HSD11B2, converting cortisol to cortisone, and the PG-inactivating enzyme 15-hydroxyprostaglandin dehydrogenase (PGDH; 601688) gene expression in the placenta of patients with preeclampsia (see 189800). When comparing matched pairs, there were 3-fold lower HSD11B2/glyceraldehyde-3-phosphate dehydrogenase (GAPDH; 138400) mRNA levels in placentas of patients with preeclampsia than in controls. They also found a 2-fold reduction in placental PGDH/GAPDH mRNA concentrations. PGDH and HSD11B2 mRNA levels correlated significantly. In term placenta, HSD11B2/GAPDH, but not PGDH, showed a significant correlation to birth weight and to placental weight. The authors concluded that, in preeclampsia, HSD11B2 mRNA expression is reduced, leading to a decrease of HSD11B2 activity. Furthermore, by means of an autocrine or paracrine mechanism, the diminished conversion of placental cortisol may lead to reduced PGDH mRNA expression.
Heilmann et al. (2001) evaluated the activity of renal 11-beta-HSD in patients with pregnancy-induced hypertension. They measured urinary free cortisol and cortisone in patients with and without pregnancy-induced hypertension and calculated the urinary free cortisol to free cortisone ratio, which is well accepted as a correlate of the activity of renal 11-beta-HSD. The free cortisol to free cortisone ratio was significantly higher in the group with pregnancy-induced hypertension (0.47 +/- 0.25 vs 0.31 +/- 0.12, p less than 0.00002). Within this group, the patients with blood pressure in the uppermost quartile had a significantly higher free cortisol to free cortisone ratio than those in the lowest quartile. The authors concluded that a reduction of the activity of 11-beta-HSD is a relevant factor for the development of pregnancy-induced hypertension. Whether the ratio of urinary free cortisol to free cortisone is a useful risk factor for the development of pregnancy-induced hypertension remained to be investigated.
Molecular Genetics
11-Beta-Ketoreductase Deficiency Causing Apparent Mineralocorticoid Excess
In 9 patients from 8 families with apparent mineralocorticoid excess (AME; 218030) and hypertension, Mune et al. (1995)identified 7 different mutations in the HSD11B2 gene (see, e.g., 614232.0001 and 614232.0002). All patients were homozygous or compound heterozygous for the mutations. In vitro functional expression studies showed that the mutant enzymes had decreased or undetectable enzyme activity compared to controls.
In affected members of a large consanguineous Sardinian pedigree with AME, Li et al. (1998) found a homozygous mutation in the HSD11B2 gene (R279C; 218030.0006). Expression of the HSD11B2 mutant cDNA resulted in an enzyme with reduced maximum velocity, but similar substrate affinity, compared with activity of the wildtype cDNA.
Odermatt et al. (2001) provided evidence for a role of glutamic acid-115 in determining cofactor-binding specificity of HSD11B2, emphasizing the importance of structure-function analysis to elucidate the molecular mechanism of apparent mineralocorticoid excess.
In the patient reported by Werder et al. (1974), Atanasov et al. (2007) identified compound heterozygosity for 2 mutations in the HSD11B2 gene (614232.0011 and 614232.0012).
Possible Role in Hypertension
Salt-sensitive (SS) subjects increase their blood pressure with increasing salt intake. Because steroid hormones modulate renal sodium retention, Lovati et al. (1999) hypothesized that the activity of the HSD11B2 enzyme is impaired in SS subjects as compared with salt-resistant (SR) subjects. The HSD11B2 enzyme inactivates 11-hydroxysteroids in the kidney, thus protecting the nonselective mineralocorticoid receptor from occupation by glucocorticoids. Lovati et al. (1999) performed an association study using a single AluI polymorphism in exon 3 and a polymorphic microsatellite marker of the HSD11B2 gene in 149 normotensive white males (37 SS and 112 SR). The activity of the HSD11B2 enzyme was assessed by determining the urinary ratio of cortisol (THF + 5-alpha-THF) to cortisone (THE) metabolites by gas chromatography in all 37 SS subjects and in 37 age- and body habitus-matched SR volunteers. Mean cortisol-to-cortisone ratio was markedly elevated in SS subjects compared with SR subjects, indicating enhanced access of glucocorticoids to the mineralocorticoid receptor in SS subjects. In 58% of SS subjects this ratio was higher than the maximum levels in SR subjects. The salt-induced elevation in arterial pressure increased with increasing cortisol-to-cortisone ratio. A total of 12 alleles of the polymorphic microsatellite marker were detected. Homozygosity for allele A7 was higher in SS subjects than in SR subjects (41% vs 28%, p less than 0.005), whereas the occurrence of allele A7 with allele A8 was lower in SS subjects than in SR subjects (8% vs 15%, p less than 0.03). The prevalence of salt sensitivity was 35% in subjects with allele A7/A7, whereas salt sensitivity was present in only 9% of the subjects with allele A7/A8. The cortisol-to-cortisone ratio was higher in subjects homozygous for the A7 microsatellite allele as compared with the corresponding control subjects. The authors concluded that decreased HSD11B2 activity in SS subjects indicates that this enzyme is involved in salt-sensitive blood pressure response in humans, and that the association of a polymorphic microsatellite marker of the gene with a reduced HSD11B2 activity suggests that variants of the HSD11B2 gene contribute to enhanced blood pressure response to salt in humans.
Genotype/Phenotype Correlations
Nunez et al. (1999) identified 4 novel and 3 previously reported HSD11B2 mutations in 4 patients with AME. Transfection experiments showed that 2 of the mutations abolished activity in whole cells, but that 3 others retained significant activity. In regression analyses of all AME patients with published genotypes, several biochemical and clinical parameters were highly correlated with mutant enzymatic activity, which was demonstrated in whole cells, with cortisol as the substrate. The parameters included the ratio of urinary cortisone to cortisol metabolites, age at presentation, and birth weight. Approximately 5% conversion of cortisol to cortisone was predicted in subjects with mutations that completely inactivate HSD11B2, suggesting that a low level of enzymatic activity is mediated by another enzyme, possibly HSD11B1.
In a review, Ferrari (2010) noted that patients with HSD11B2 mutations showed varying degrees of severity in terms of clinical and biochemical features, according to the residual in vivo activity of the mutant enzyme. Mutations can cause a spectrum of disease, ranging from life-threatening disease in early childhood to a milder form diagnosed only in adults as isolated hypertension.
Animal Model
Kotelevtsev et al. (1999) generated Hsd11b2-null mice. All of the mice appeared normal at birth, but about 50% showed motor weakness and died within 48 hours. Male and female survivors were fertile but exhibited hypokalemia, hypotonic polyuria, and apparent mineralocorticoid activity of corticosterone. Young adult Hsd11b2-null mice were markedly hypertensive with hypertrophy and hyperplasia of the epithelium of the distal tubules of the nephron; the histologic changes did not reverse with mineralocorticoid receptor antagonism. Kotelevtsev et al. (1999) concluded that Hsd11b2-null mice provide a model for the human syndrome of apparent mineralocorticoid excess.
To evaluate aldosterone activation of cardiomyocyte mineralocorticoid receptors, Qin et al. (2003) generated transgenic mice overexpressing Hsd11b2 in cardiomyocytes, thus reducing myocardial intracellular glucocorticoids and allowing aldosterone occupancy of cardiomyocyte mineralocorticoid receptors. Transgenic mice were normotensive but spontaneously developed cardiac hypertrophy, fibrosis, and heart failure, and died prematurely on a normal salt diet. Eplerenone, a selective aldosterone blocker, ameliorated this phenotype. Qin et al. (2003)concluded that these data confirmed the deleterious consequences of inappropriate activation of cardiomyocyte mineralocorticoid receptors by aldosterone and revealed a tonic inhibitory role of glucocorticoids in preventing such outcomes under physiologic conditions.
ALLELIC VARIANTS (13 Selected Examples):
Table View ClinVar
.0001 APPARENT MINERALOCORTICOID EXCESS
HSD11B2, ARG208CYS [dbSNP:rs121917780] [ClinVar]
In a 9-year-old Native American male with apparent mineralocorticoid excess (AME; 218030) and a blood pressure of 170/100, Mune et al. (1995) identified a homozygous C-to-T transition in the HSD11B gene, resulting in an arg208-to-cys (R208C) substitution.
.0002 APPARENT MINERALOCORTICOID EXCESS
HSD11B2, ARG213CYS [dbSNP:rs28934591] [ClinVar]
In 2 children of Caucasian/Native South American ancestry with apparent mineralocorticoid excess (AME; 218030), previously reported by Shackleton et al. (1985), Mune et al. (1995) found homozygosity for a C-to-T transition in the HSD11B gene, resulting in an arg213-to-cys (R213C) substitution.
In a patient with AME, Rogoff et al. (1998) described the R213C mutation in the 11-beta-HSD2 enzyme. In vitro expression studies of the mutant construct indicated that the mutant protein is normally expressed, but that its activity is abolished. The CGC-to-TGC transition at codon 213 is at a CpG dinucleotide. Because of the occurrence of an R213C mutation in several unrelated families, the authors concluded that codon 213 is a hotspot for mutations.
.0003 APPARENT MINERALOCORTICOID EXCESS
HSD11B2, ARG337CYS [dbSNP:rs121917781] [ClinVar]
In sibs with apparent mineralocorticoid excess (AME; 218030), Wilson et al. (1995) identified a homozygous C-to-T transition in the HSD11B2 gene, resulting in an arg337-to-cys (R337C) substitution. Obeyesekere et al. (1995) examined the metabolism of cortisol in mammalian cells transfected with plasmids expressing the wildtype and mutant enzymes. In whole cells the Km of the normal enzyme was 110 nM, while the enzyme containing the R337C mutation displayed a Km of 1,010 nM. The mutant enzyme was totally inactive in cell-free preparations, suggesting that it has additional properties that may compromise its activity in whole cells.
.0004 APPARENT MINERALOCORTICOID EXCESS
HSD11B2, ARG208HIS [dbSNP:rs28934592] [ClinVar]
In a Japanese patient with apparent mineralocorticoid excess (AME; 218030), Kitanaka et al. (1997) identified compound heterozygous mutations in the HSD11B2 gene: a G-to-A transition in exon 3 resulting in an arg208-to-his (R208H) substitution, and a 3-bp deletion in exon 5 (CGCTAT to CAT) resulting in an arg-to-his substitution (R337H) and deletion of a tyr residue (del338). The latter mutation was shown to abolish HSD11B2 enzymatic activity.
.0005 APPARENT MINERALOCORTICOID EXCESS
HSD11B2, ARG337HIS [dbSNP:rs397509434] [dbSNP:rs28934593] [ClinVar]
For discussion of the arg337-to-his (R337H) mutation in the HSD11B2 gene that was found in compound heterozygous state in a patient with apparent mineralocorticoid excess (AME; 218030) by Kitanaka et al. (1997), see 614232.0004.
.0006 APPARENT MINERALOCORTICOID EXCESS
HSD11B2, ARG279CYS [dbSNP:rs28934594] [ClinVar]
In affected members of a large Sardinian family with apparent mineralocorticoid excess (AME; 218030), Li et al. (1998) identified a homozygous 945C-T transition in the HSD11B2 gene, resulting in an arg279-to-cys (R279C) substitution. Expression of the mutant cDNA resulted in an enzyme with reduced maximum velocity, but similar substrate affinity, compared with activity of the wildtype cDNA. Affected individuals were more than 30 years of age and had both mineralocorticoid hypertension and evidence of impaired metabolism of cortisol to cortisone. The heterozygous state was phenotypically normal but was associated with subtle defects in cortisol metabolism. Although the family had been considered to have 'type II' AME due to a normal urinary cortisol:corticosterone metabolite ratio, Li et al. (1998)concluded that their molecular studies demonstrated that the classification of AME into subtypes is inappropriate because AME represents a spectrum of mineralocorticoid hypertension with severity reflecting the underlying genetic defect in the HSD11B2 gene.
.0007 APPARENT MINERALOCORTICOID EXCESS, MILD
HSD11B2, PRO227LEU [dbSNP:rs121917782] [ClinVar]
In a female patient from a consanguineous Mennonite family with a mild form of apparent mineralocorticoid excess (AME; 218030), Wilson et al. (1998) identified a homozygous C-to-T transition in the HSD11B2 gene, resulting in a pro227-to-leu (P227L) substitution. She had low-renin hypertension but did not demonstrate the typical features of AME. Biochemical analysis revealed a moderately elevated cortisol-to-cortisone metabolite ratio. The conversion of cortisol to cortisone was 58% compared to 0 to 6% in patients with typical AME (the normal conversion is 90-95%). The parents and sibs were heterozygous for this mutation. Because approximately 40% of patients with essential hypertension demonstrate low renin, Wilson et al. (1998)suggested that such patients should undergo genetic analysis of the HSD11B2 gene.
In an extensive review of steroid disorders in children, specifically congenital adrenal hyperplasia and apparent mineralocorticoid excess, New and Wilson (1999) provided further information concerning what they alleged was the first reported patient with a mild form of AME. Asymptomatic hypertension was diagnosed at age 12.5 years during a sports physical. The parents were consanguineous Mennonites of Prussian descent (Alexanderwohl Church). The only family member with hypertension was the maternal grandmother. Although the patient lacked hypokalemia and low birthweight and had only mild hypertension, New and Wilson (1999) established a diagnosis for AME genetically.
.0008 APPARENT MINERALOCORTICOID EXCESS, MILD
HSD11B2, 6-BP DEL, LEU114/GLU115 [dbSNP:rs794726669] [ClinVar]
Odermatt et al. (2001) reported 2 sibs, aged 1 and 2 years, who were diagnosed with hypokalemic hypertension and low plasma aldosterone and renin levels, indicating mineralocorticoid hypertension (AME; 218030). Analysis of urinary steroid metabolites showed a markedly impaired metabolism of cortisol and nearly absent urinary free cortisone. Although phenotypically normal, the heterozygous parents showed a disturbed cortisol metabolism. Genetic analysis of the HSD11B2 gene from the AME patients revealed the homozygous deletion of 6 nucleotides in exon 2, with the resultant loss of amino acids leu114 and glu115, representing the first alteration found in the cofactor-binding domain. The deletion mutant, expressed in HEK293 cells, showed an approximately 20-fold lower maximum velocity but increased apparent affinity for cortisol and corticosterone. Functional analysis of wildtype and mutant proteins indicated that a disturbed conformation of the cofactor-binding domain, but not the missing negative charge of glu115, led to the observed decreased activity of the deletion mutant. The authors concluded that their findings provided evidence for a role of glu115 in determining cofactor-binding specificity of HSD11B2 and emphasized the importance of structure-function analysis to elucidate the molecular mechanism of apparent mineralocorticoid excess.
.0009 APPARENT MINERALOCORTICOID EXCESS
HSD11B2, ASP223ASN [dbSNP:rs121917833] [ClinVar]
In a 4-year-old male with apparent mineralocorticoid excess (AME; 218030) and arterial hypertension, Carvajal et al. (2003)detected 2 homozygous mutations in the HSD11B2 gene, a G-to-A transition in exon 4 resulting in an asp223-to-asn substitution (D223N) and a C-to-T substitution in intron 3 (7279C-T; 614232.0011). The patient's plasma renin activity and serum aldosterone were undetectable in the presence of a high cortisol-to-cortisone ratio. The mutant enzyme had only 6% of wildtype activity in transfected Chinese hamster ovary (CHO) cells. In silico 3D modeling showed that D223N changed the enzyme's surface electrostatic potential affecting the cofactor and substrate enzyme-binding capacity. Mune et al. (1995) had described the 7279C-T transition (IVS3+14C-T) and predicted it to alter the normal splicing of pre-mRNA, given a nonfunctional protein. Thus, if some mutated RNA were translated, it would carry the D223N mutation that almost abolishes enzymatic activity. Carvajal et al. (2003) concluded that these findings may determine the full inactivation of this enzyme, explaining the biochemical profile and the early onset of hypertension seen in this patient.
.0010 APPARENT MINERALOCORTICOID EXCESS
HSD11B2, TYR299DEL [dbSNP:rs794726670] [ClinVar]
In an 11-year-old Pakistani girl, born of consanguineous parents, with apparent mineralocorticoid excess (AME; 218030), Lin-Su et al. (2004) found homozygous deletion of the tyr299 (Y299) codon in exon 5 of the HSD11B2 gene. The patient presented at age 9 years with hypertension (225/120 mm Hg), low plasma renin activity, hypokalemic metabolic alkalosis, suppressed aldosterone, and bilateral nephrocalcinosis. She had had a low birth weight compared with her sibs. Biochemical analysis showed an elevated urinary cortisol-to-cortisone metabolites ratio (tetrahydrocortisol and 5-alpha-tetrahydrocortisol/tetrahydrocortisone) of 28 (normal, 0.66-2.44). She had a cortisol secretion rate of 0.43 mg/d (normal, 5-25 mg/d). In vitro expression in CHO cells revealed that this mutation resulted in no activity.
.0011 APPARENT MINERALOCORTICOID EXCESS
HSD11B2, IVS3DS, C-T, +14
In a 26-year-old Mexican American woman with apparent mineralocorticoid excess (AME; 218030), Mune et al. (1995)identified a homozygous splice site mutation in the HSD11B2 gene (IVS3+14C-T).
.0012 APPARENT MINERALOCORTICOID EXCESS
HSD11B2, TYR338HIS [dbSNP:rs387907117] [ClinVar]
In a woman with apparent mineralocorticoid excess (AME; 218030), originally reported by Werder et al. (1974), Atanasov et al. (2007) identified compound heterozygosity for 2 mutations in the HSD11B2 gene: a 2-bp deletion (CA) in exon 1, resulting in premature termination (614232.0013), and a T-to-C transition in exon 5, resulting in a tyr338-to-his (Y338H) substitution. Neither mutation was found in 300 control chromosomes. In vitro functional expression studies in HEK293 cells showed reduced levels of the Y338H mutant protein (45% lower than wildtype) as well as significantly decreased activity (less than 5% of wildtype), although there was no defect in substrate affinity. Site-directed mutagenesis studies indicated that tyr338 is absolutely essential for enzyme activity and that a cluster including residues 335 to 339 is necessary for protein stability. Subcellular distribution studies showed abnormal localization of the mutant Y338H protein, suggesting misfolding and reduced protein stability. Further studies indicated proteasome-mediated degradation. There was some recovery of activity using chemical chaperones and low temperature. The findings indicated that impaired protein stability of HSD11B2 contributed to the development of hypertension in this patient.
.0013 APPARENT MINERALOCORTICOID EXCESS
HSD11B2, 2-BP DEL
For discussion of the 2-bp deletion (CA) in exon 1 of the HSD11B2 gene that was found in compound heterozygous state in a patient with apparent mineralocorticoid excess (AME; 218030) by Atanasov et al. (2007), see
OMIM Entry - * 614232 - 11-BETA-HYDROXYSTEROID DEHYDROGENASE, TYPE II; HSD11B2
