Late-onset apparent mineralocorticoid excess caused by novel compound heterozygous mutations in the HSD11B2 gene

Mutations in the gene encoding 11beta-hydroxysteroid dehydrogenase type 2, 11beta-HSD2 (HSD11B2), explain the molecular basis for the syndrome of apparent mineralocorticoid excess (AME), characterized by severe hypertension and hypokalemic alkalosis. Cortisol is the offending mineralocorticoid in AME, as the result of a lack of 11beta-HSD2-mediated cortisol to cortisone inactivation. In this study, we describe mutations in the HSD11B2 gene in 3 additional AME kindreds in which probands presented in adult life, with milder phenotypes including the original seminal case reported by Stewart and Edwards. Genetic analysis of the HSD11B2 gene revealed that all probands were compound heterozygotes, for a total of 7 novel coding and noncoding mutations. Of the 7 mutations detected, 6 were investigated for their effects on gene expression and enzyme activity by the use of mutant cDNA and minigene constructs transfected into HEK 293 cells. Four missense mutations resulted in enzymes with varying degrees of activity, all <10% of wild type. A further 2 mutations generated incorrectly spliced mRNA and predicted severely truncated, inactive enzyme. The mothers of 2 probands heterozygous for missense mutations have presented with a phenotype indistinguishable from "essential" hypertension. These genetic and biochemical data emphasize the heterogeneous nature of AME and the effects that heterozygosity at the HSD11B2 locus can have on blood pressure in later life.     

Apparent mineralocorticoid excess.

Apparent mineralocorticoid excess (AME) is a potentially fatal genetic disorder causing severe juvenile hypertension, pre- and postnatal growth failure, hypokalemia and low to undetectable levels of renin and aldosterone. It is caused by autosomal recessive mutations in the HSD11B2 gene, which result in a deficiency of 11 beta-hydroxysteroid dehydrogenase type 2 (11 beta-HSD2). The 11 beta-HSD2 enzyme is responsible for the conversion of cortisol to the inactive metabolite cortisone and, therefore, protects the mineralocorticoid receptors from cortisol intoxication. In 1998, a mild form of this disease was reported, which might represent an important cause of low-renin hypertension. Early and vigilant treatment might prevent or improve the morbidity and mortality of end-organ damage.     

Apparent mineralocorticoid excess syndrome: an overview

Apparent mineralocorticoid excess (AME) syndrome results from defective 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2). This enzyme is co-expressed with the mineralocorticoid receptor (MR) in the kidney and converts cortisol (F) to its inactive metabolite cortisone (E). Its deficiency allows the unmetabolized cortisol to bind to the MR inducing sodium retention, hypokalemia, suppression of PRA and hypertension. Mutations in the gene encoding 11beta-HSD2 account for the inherited form, but a similar clinical picture to AME occurs following the ingestion of bioflavonoids, licorice and carbenoxolone, which are competitive inhibitors of 11beta-HSD2. Reduced 11beta-HSD2 activity may explain the increased sodium retention in preeclampsia, renal disease and liver cirrhosis. Relative deficiency of 11beta-HSD2 activity can occur in Cushing's syndrome due to saturation of the enzyme and explains the mineralocorticoid excess state that characterizes ectopic ACTH syndrome. Reduced placental 11beta-HSD2 expression might explain the link between reduced birth weight and adult hypertension. Polymorphic variability in the HSD11B2 gene in part determines salt sensitivity, a forerunner for adult hypertension onset. AME represents a spectrum of mineralocorticoid hypertension with severity reflecting the underlying genetic defect in the 11beta-HSD2; although AME is a genetic disorder, several exogenous compounds can bring about the symptoms by inhibiting 11beta-HSD2 enzyme. Substrate excess as seen in Cushing's syndrome and ACTH ectopic production can overwhelm the capacity of 11beta-HSD2 to convert F to E, leading up to an acquired form of AME.     

Analysis of the 11beta-hydroxysteroid dehydrogenase type 2 gene (HSD11B2) in human essential hypertension

BACKGROUND: The HSD11B2 gene, encoding the kidney isoenzyme 11beta-hydroxysteroid dehydrogenase, is a candidate for essential hypertension. We previously showed that the frequency of shorter alleles of a CA repeat polymorphism in the first intron of 11beta-HSD2 gene was significantly higher among salt-sensitive than salt-resistant individuals with hypertension. The aim of the study was to analyze the HSD11B2 gene to assess whether some of its variants might be involved in hypertension. METHODS: Exons 2, 3, 4, and 5 were screened by polymerase chain reaction-single-strand conformation polymorphism analysis in 292 hypertensive patients and 163 control subjects. The samples with variant electrophoretic patterns at single-strand conformation polymorphism were re-analyzed using an automated DNA sequencer. A case-control study was then performed by comparing genotype frequencies in hypertensive and normotensive subjects. RESULTS: Analysis of the HSD11B2 showed that in hypertensive patients there is a higher prevalence of two associated polymorphisms, Thr156/Thr(C468A) in exon 2 (ex2) and Glu178/Glu(G534A) in exon 3 (ex3), than in normotensive subjects (9% v 2.4%). This association did not correlate with salt sensitivity. C468A alone correlates significantly with hypertension (9%) and was identified only in 3% of control subjects (P < .05), whereas G534A was identified also in about 7% of normotensive subjects. The urinary free cortisol/urinary free cortisone ratio (UFF/UFE) was significantly higher in hypertensive patients compared with control subjects (P < .01). CONCLUSIONS: Two different polymorphisms of the HSD11B2 gene were observed. The association of both polymorphisms was significantly higher in hypertensive subjects than in control subjects. Its role should be further investigated, but it could be related to other mutations in the promoter region of HSD11B2 or to the modulation of 11beta-HSD2 mRNA processing in hypertensive subjects.     

The role of the 11beta-hydroxysteroid dehydrogenase type 2 in human hypertension

The 11 beta-hydroxysteroid dehydrogenase type 2 (11 PHSD2) enzyme inactivates 11 betahydroxy steroids in sodium-transporting epithelia such as the kidney, thus protecting the non-selective mineralocorticoid receptor (MR) from occupation by cortisol in humans. Inhibition by xenobiotics such as liquorice or mutations in the HSD11 B2 gene, as occur in the rare monogenic hypertensive syndrome of apparent mineralocorticoid excess (AME), result in a compromised 11 betaHSD2 enzyme activity, which in turn leads to overstimulation of the MR by cortisol, sodium retention, hypokalaemia, low plasma renin and aldosterone concentrations, and hypertension. Whereas the first patients described with AME had a severe form of hypertension and metabolic derangements, with an increased urinary ratio of cortisol (THF+5alphaTHF) to cortisone (THE) metabolites, more subtle effects of mild 11 beta HSD2 deficiency on blood pressure have recently been observed. Hypertension with no other characteristic signs of AME was found in the heterozygous father of a child with AME, and we described a girl with a homozygous gene mutation resulting in only a slightly reduced 11 beta HSD2 activity causing 'essential' hypertension. Thus, depending on the degree of loss of enzyme activity, 11 beta HSD2 mutations can cause a spectrum of phenotypes ranging from severe, life-threatening hypertension in infancy to a milder form of the disease in adults. Patients with essential hypertension usually do not have overt signs of mineralocorticoid excess, but nevertheless show a positive correlation between blood pressure and serum sodium levels, or a negative correlation with potassium concentrations, suggesting a mineralocorticoid influence. Recent studies revealed a prolonged half-life of cortisol and an increased ratio of urinary cortisol to cortisone metabolites in some patients with essential hypertension. These abnormalities may be genetically determined. A genetic association of a HSD11 B2 flanking microsatellite and hypertension in black patients with end-stage renal disease has been reported. A recent analysis of a CA-repeat allele polymorphism in unselected patients with essential hypertension did not find a correlation between this marker and blood pressure. Since steroid hormones with mineralocorticoid action modulate renal sodium retention, one might hypothesize that genetic impairment of 11 beta HSD2 activity would be more prevalent in salt-sensitive as compared with salt-resistant subjects. Accordingly, we found a significant association between the polymorphic CA-microsatellite marker and salt-sensitivity. Moreover, the mean ratio of urinary cortisol to cortisone metabolites, as a measure for 11betaHSD2 activity, was markedly elevated in salt-sensitive subjects. These findings suggest that variants of the HSD11 B2 gene may contribute to the enhanced blood pressure response to salt in some humans.     

In vitro expression studies of a novel mutation delta299 in a patient affected with apparent mineralocorticoid excess

Apparent mineralocorticoid excess syndrome (AME) is an autosomal recessive disorder that results in low renin hypertension and other characteristic clinical features. Typical patients present with severe hypertension, hypokalemia, and undetectable aldosterone. Most patients also have low birth weight, failure to thrive, and nephrocalcinosis. The 11betahydroxysteroid dehydrogenase type 2 (11betaHSD2) defect is documented by demonstrating a failure to convert cortisol to cortisone. Here, we report a patient with typical phenotypic features of AME who does not carry any of the previously described mutations in the HSD11B2 gene. This female patient from a consanguineous Pakistani family presented at age 9 yr. She had a low birth weight compared with her siblings and presented with hypertension (225/120 mm Hg), low plasma renin activity, hypokalemic metabolic alkalosis, suppressed aldosterone, and bilateral nephrocalcinosis. Echocardiogram did not reveal left ventricular hypertrophy, and baseline ophthalmological evaluation did not demonstrate hypertensive retinopathy. However, at age 12 yr, she developed mild to moderate hypertensive retinopathy. Biochemical analysis showed an elevated urinary cortisol to cortisone metabolites ratio (tetrahydrocortisol and 5alpha-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). Sequence analysis of the HSD11B2 gene revealed a novel homozygous delta299 mutation in exon 5. In vitro expression in Chinese hamster ovary cells revealed that this mutation resulted in no activity.     

Hypertension and the cortisol-cortisone shuttle

11 beta-Hydroxysteroid dehydrogenase type 2 (11 beta-HSD2) plays a crucial role in converting hormonally active cortisol to inactive cortisone, thereby conferring specificity on the mineralocorticoid receptor. Mutations in the gene encoding 11 beta-HSD2 (HSD11B2) account for an inherited form of hypertension, the syndrome of apparent mineralocorticoid excess, in which cortisol induces hypertension and hypokalemia. A similar clinical picture to apparent mineralocorticoid excess occurs after the ingestion of licorice and carbenoxolone, which are competitive inhibitors of 11 beta-HSD2. Reduced 11 beta-HSD2 activity may explain the increased sodium retention in preeclampsia, renal disease, and liver cirrhosis. Substrate saturation of 11 beta-HSD2 occurs in Cushing's syndrome and explains the mineralocorticoid excess state that characterizes ectopic ACTH syndrome. Polymorphic variability in the HSD11B2 gene in part determines salt sensitivity, a forerunner for adult onset hypertension. Furthermore, reduced placental 11 beta-HSD2 expression might underpin the Barker hypothesis, the epidemiological link between reduced birth weight and adult hypertension. At a prereceptor level, 11 beta-HSD2 plays a key role in normal physiology in the corticosteroid regulation of sodium homeostasis and pathophysiology of hypertension.     

Cortisol metabolism in hypertension

Corticosteroids are critically involved in blood pressure regulation. Lack of adrenal steroids in Addison's disease causes life-threatening hypotension, whereas glucocorticoid excess in Cushing's syndrome invariably results in high blood pressure. At a pre-receptor level, glucocorticoid action is modulated by 11beta-hydroxysteroid dehydrogenases (11beta-HSDs). 11Beta-HSD1 activates cortisone to cortisol to facilitate glucocorticoid receptor (GR)-mediated action. By contrast, 11beta-HSD2 plays a pivotal role in aldosterone target tissues where it catalyses the opposite reaction (i.e. inactivation of cortisol to cortisone) to prevent activation of the mineralocorticoid receptor (MR) by cortisol. Mutations in the 11beta-HSD2 gene cause a rare form of inherited hypertension, the syndrome of apparent mineralocorticoid excess (AME), in which cortisol activates the MR resulting in severe hypertension and hypokalemia. Ingestion of competitive inhibitors of 11beta-HSD2 such as liquorice and carbenoxolone result in a similar but milder clinical phenotype. Epidemiological data suggests that polymorphic variability in the HSD11B2 gene determines salt sensitivity in the general population, which is a key predisposing factor to adult onset hypertension in some patients. Extrarenal sites of glucocorticoid action and metabolism that might impact on blood pressure include the vasculature and the central nervous system. Intriguingly, increased exposure to glucocorticoids during fetal life promotes high blood pressure in adulthood suggesting an early programming effect. Thus, metabolism and action in many peripheral tissues might contribute to the pathophysiology of human hypertension.     

A genetic defect resulting in mild low-renin hypertension

Severe low-renin hypertension has few known causes. Apparent mineralocorticoid excess (AME) is a genetic disorder that results in severe juvenile low-renin hypertension, hyporeninemia, hypoaldosteronemia, hypokalemic alkalosis, low birth weight, failure to thrive, poor growth, and in many cases nephrocalcinosis. In 1995, it was shown that mutations in the gene (HSD11B2) encoding the 11β-hydroxysteroid dehydrogenase type 2 enzyme (11β-HSD2) cause AME. Typical patients with AME have defective 11β-HSD2 activity, as evidenced by an abnormal ratio of cortisol to cortisone metabolites and by an exceedingly diminished ability to convert [11-³H]cortisol to cortisone. Recently, we have studied an unusual patient with mild low-renin hypertension and a homozygous mutation in the HSD11B2 gene. The patient came from an inbred Mennonite family, and though the mutation identified her as a patient with AME, she did not demonstrate the typical features of AME. Biochemical analysis in this patient revealed a moderately elevated cortisol to cortisone metabolite ratio. The conversion of cortisol to cortisone was 58% compared with 0–6% in typical patients with AME whereas the normal conversion is 90–95%. Molecular analysis of the HSD11B2 gene of this patient showed a homozygous C→T transition in the second nucleotide of codon 227, resulting in a substitution of proline with leucine (P227L). The parents and sibs were heterozygous for this mutation. In vitro expression studies showed an increase in the K_m (300 nM) over normal (54 nM). Because ≈40% of patients with essential hypertension demonstrate low renin, we suggest that such patients should undergo genetic analysis of the HSD11B2 gene.     

A mutation in the cofactor-binding domain of 11beta-hydroxysteroid dehydrogenase type 2 associated with mineralocorticoid hypertension

Renal 11beta-hydroxysteroid dehydrogenase type 2 (11betaHSD2) is an enzyme responsible for the peripheral inactivation of cortisol to cortisone in mineralocorticoid target tissues. Mutations in the gene encoding 11betaHSD2 cause the syndrome of apparent mineralocorticoid excess (AME), an autosomal recessive form of inherited hypertension, in which cortisol acts as a potent mineralocorticoid. The mutations reported to date have been confined to exons 3-5. Here, we describe two siblings, 1 and 2 yr old, who were diagnosed with hypokalemic hypertension and low plasma aldosterone and renin levels, indicating mineralocorticoid hypertension. Analysis of urinary steroid metabolites showed a markedly impaired metabolism of cortisol, with (tetrahydrocortisol + 5alpha-tetrahydrocortisol)/tetrahydrocortisone ratios of 40-60, 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 six nucleotides in exon 2 with the resultant loss of amino acids Leu(114) and Glu(115), representing the first alteration found in the cofactor-binding domain. The deletion mutant, expressed in HEK-293 cells, showed an approximately 20-fold lower maximum velocity but increased apparent affinity for cortisol and corticosterone. In contrast, two additionally constructed substitutions, Glu(115) to Gln or Lys, showed increased maximal velocity and apparent affinity for 11beta-hydroxyglucocorticoids. Functional analysis of wild-type and mutant proteins indicated that a disturbed conformation of the cofactor-binding domain, but not the missing negative charge of Glu(115), led to the observed decreased activity of the deletion mutant. Considered together, these findings provide evidence for a role of Glu(115) in determining cofactor-binding specificity of 11betaHSD2 and emphasize the importance of structure-function analysis to elucidate the molecular mechanism of AME.     

Tissue-specific Cushing's syndrome, 11beta-hydroxysteroid dehydrogenases and the redefinition of corticosteroid hormone action

Two isoforms of 11beta-hydroxysteroid dehydrogenase (11beta-HSD) interconvert the active glucocorticoid, cortisol, and inactive cortisone. 11beta-HSD1 acts predominantly as an oxo-reductase in vivo using NADP(H) as a cofactor to generate cortisol. In contrast, 11beta-HSD2 is a NAD-dependent dehydrogenase inactivating cortisol to cortisone, thereby protecting the mineralocorticoid receptor from occupation by cortisol. In peripheral tIssues, both enzymes serve to control the availability of cortisol to bind to corticosteroid receptors. 11beta-HSD2 protects the mineralocorticoid receptor from cortisol excess; mutations in the HSD11B2 gene explain an inherited form of hypertension, the syndrome of 'apparent mineralocorticoid excess', in which 'Cushing's disease of the kidney' results in cortisol-mediated mineralocorticoid excess. Inhibition of 11beta-HSD2 explains the mineralocorticoid excess state seen following liquorice ingestion and more subtle defects in enzyme expression might be involved in the pathogenesis of 'essential' hypertension. 11beta-HSD1 by generating cortisol in an autocrine fashion facilitates glucocorticoid receptor-mediated action in key peripheral tIssues including liver, adipose tissue, bone and the eye. 'Cushing's disease of the omentum' has been proposed as an underlying mechanism in the pathogenesis of central obesity and raises the exciting possibility of selective 11beta-HSD1 inhibition as a novel therapy for patients with the metabolic syndrome. 'Pre-receptor' metabolism of cortisol via 11beta-HSD isozymes is an important facet of corticosteroid hormone action. Aberrant expression of these isozymes is involved in the pathogenesis of diverse human diseases including hypertension, insulin resistance and obesity. Modulation of enzyme activity may offer a future therapeutic approach to treating these diseases whilst circumventing the endocrine consequences of glucocorticoid excess or deficiency.     

Two homozygous mutations in the 11 beta-hydroxysteroid dehydrogenase type 2 gene in a case of apparent mineralocorticoid excess

The human microsomal 11 beta-hydroxysteroid dehydrogenase type 2 (11 beta HSD2) metabolizes active cortisol into cortisone and protects the mineralocorticoid receptor from glucocorticoid occupancy. In a congenital deficiency of 11 beta-HSD2, the protective mechanism fails and cortisol gains inappropriate access to mineralocorticoid receptor, resulting in low-renin hypertension and hypokalemia. In the present study, we describe the clinical and molecular genetic characterization of a patient with a new mutation in the HSD11B2 gene. This is a 4-yr-old male with arterial hypertension. The plasma renin activity and serum aldosterone were undetectable in the presence of a high cortisol to cortisone ratio. PCR amplification and sequence analysis of HSD11B2 gene showed the homozygous mutation in exon 4 Asp223Asn (GAC-->AAC) and a single nucleotide substitution C-->T in intron 3. Using site-directed mutagenesis, we generated a mutant 11 beta HSD2 cDNA containing the Asp223Asn mutation. Wild-type and mutant cDNA was transfected into Chinese hamster ovary cells and enzymatic activities were measured using radiolabeled cortisol and thin-layer chromatography. The mRNA and 11 beta HSD2 protein were detected by RT-PCR and Western blot, respectively. Wild-type and mutant 11 beta HSD2 protein was expressed in Chinese hamster ovary cells, but the mutant enzyme had only 6% of wild-type activity. In silico 3D modeling showed that Asp223Asn changed the enzyme's surface electrostatic potential affecting the cofactor and substrate enzyme-binding capacity. The single substitution C-->T in intron 3 (IVS3 + 14 C-->T) have been previously reported that alters the normal splicing of pre-mRNA, given a nonfunctional protein. These findings may determine the full inactivation of this enzyme, explaining the biochemical profile and the early onset of hypertension seen in this patient.     

Arginine vasopressin stimulates 11beta-hydroxysteroid dehydrogenase type 2 expression in the mineralocorticosteroid target cells

11Beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2) deficiency causes sodium retention and severe hypertension by allowing glucocorticoids access to the non-selective mineralocorticosteroid receptor. Understanding regulation of the HSD11B2 gene is thus of fundamental importance in hypertension research. A number of studies have suggested that second messenger pathways may be important in this regard. In the present study we show that HSD11B2 expression in human renal epithelial P58 cells is regulated at the mRNA and protein level, and that protein kinases A (PKA) and C (PKC) are involved in this process. PKA stimulation resulted in almost two-fold increase while PKC activation in almost two-fold decrease in the HSD11B2 mRNA and protein level. Western blot analysis revealed a dimeric form of 11beta-HSD2 of about 80kDa. Arginine vasopressin (AVP), acting through the AVP2 receptor, as well as 11beta-HSD2 substrates, corticosterone and dexamethasone, up-regulate HSD11B2 expression, suggesting their role as possible factors affecting blood pressure. We show that the activators of the PKA pathway induce, while activators of PKC pathway repress the expression of HSD11B2 in human renal epithelial cells. AVP, acting via the PKA pathway, might be a physiological stimulator of the HSD11B2 expression. The 11beta-HSD2 substrates, both natural (corticosterone) and synthetic (dexamethasone), might protect the mineralocorticosteroid-target cells against cortisol excess.     

Mutations in the 11β-Hydroxysteroid Dehydrogenase Type II Enzyme Associated with Hypertension and Possibly Stillbirth

The 11β-hydroxysteroid dehydrogenase type II enzyme (11ßHSD2) converts cortisol into cortisone, thus preventing occupation of the non-selective mineralocorticoid receptor by glucocorticoids in the kidney. Placental 11ßHSD2 is also thought to protect the fetus from the high maternal circulating levels of glucocorticoids. Mutations generating inactive enzymes have been described in the HSD11B2 gene in the congenital syndrome of apparent mineralocorticoid excess (AME) — a low renin form of hypertension. Recently, a mutation has been identified in a family with AME and in which there is a high incidence of stillbirths. In this study we have expressed the R374X mutation and show that the mutant is devoid of enzyme activity in intact mammalian cells expressing a significant level of the truncated protein. While this observation elucidates the cause of AME in this family the degree to which R374X also contributes to the higher incidence of failed pregnancies remains to be determined.     

Genetic variations of HSD11B2 in hypertensive patients and in the general population, six rare missense/frameshift mutations.

Mutations in the gene encoding 11beta-hydroxysteroid dehydrogenase type 2, HSD11B2, cause a rare monogenic juvenile hypertensive syndrome called apparent mineralocorticoid excess (AME). In AME, defective HSD11B2 enzyme activity results in overstimulation of the mineralocorticoid receptor (MR) by cortisol, causing sodium retention, hypokalemia, and salt-dependent hypertension. Here, we have studied whether genetic variations in HDS11B2 are implicated in essential hypertension in Japanese hypertensives and the general population. By sequencing the entire coding region and the promoter region of HDS11B2 in 953 Japanese hypertensives, we identified five missense mutations in 11 patients (L14F, n = 5; R74H, n = 1; R147H, n = 3; T156I, n = 1; R335H, n = 1) and one novel frameshift mutation (4884Gdel, n = 1) in a heterozygous state, in addition to 19 genetic variations. All genetic variations identified were rare, with minor allele frequencies less than 0.005. Four of 12 patients with the missense/frameshift mutations showed renal failure. Four missense mutations, L14F, R74H, R147H, and R335H, were successfully genotyped in the general population, with a sample size of 3,655 individuals (2,175 normotensives and 1,480 hypertensives). Mutations L14F, R74H, R147H, and R335H were identified in hypertensives (n = 6, 8, 3, and 0, respectively) and normotensives (n = 8, 12, 5, and 0, respectively) with a similar frequency, suggesting that these missense mutations may not strongly affect the etiology of essential hypertension. Since the allele frequency of all of the genetic variations identified in this study was rare, an association study was not conducted. Taken together, our results indicate that missense mutations in HSD11B2 do not substantially contribute to essential hypertension in Japanese.     

Substitution mutation C268Y causes 17 beta-hydroxysteroid dehydrogenase 3 deficiency

The 17 beta-hydroxysteroid dehydrogenase (HSD) type 3 isozyme catalyzes the conversion of androstenedione to testosterone in the testis. Deleterious mutations in the HSD17B3 gene cause undermasculinization in genetic males attributable to impaired testosterone biosynthesis. Hence, a hallmark of this autosomal recessive disorder is a decreased plasma testosterone-to-androstenedione ratio. Here, a novel C268Y substitution mutation in exon 10 of the HSD17B3 gene, in a subject with 17 beta-HSD 3 deficiency, is reported. Reconstitution experiments with recombinant protein reveal that substitution of tyrosine for cysteine at position 268 of 17 beta-HSD type 3 abrogates the enzymatic activity. This finding brings to 20 the number of mutations in the HSD17B3 gene that cause male undermasculinization.     

Association studies between microsatellite markers within the gene encoding human 11beta-hydroxysteroid dehydrogenase type 1 and body mass index,waist to hip ratio,and glucocorticoid metabolism

Two isozymes of 11beta-hydroxysteroid dehydrogenase (11beta-HSD) interconvert active cortisol (F) and inactive cortisone (E). 11beta-HSD1 is an oxo-reductase (E to F) expressed in several glucocorticoid target tissues, including liver and adipose tissue, where it facilitates glucocorticoid-induced gluconeogenesis and adipocyte differentiation, respectively. We have isolated a full-length HSD11B1 genomic clone; the gene is more than 30 kb in length, not 9 kb in length as previously reported, principally due to a large intron 4. Two polymorphic (CA)(n) repeats have been characterized within intron 4: a CA(19) repeat 2.7 kb 3' of exon 4 and a CA(15) repeat 3 kb 5' of exon 5. The microsatellites, CA(19) and CA(15), were PCR amplified using fluorescent primers and were genotyped on an ABI 377 DNA sequencer from DNA of 413 normal individuals enrolled in the MONICA study of cardiovascular risk factors and 557 Danish men (ADIGEN study), of whom 234 were obese [body mass index (BMI), >/=31 kg/m(2) ] at draft board examination and 323 were randomly selected controls from the draftee population with BMI below 31 kg/m(2) (mean +/- SE, 21.7 +/- 0.41). Genotypic data from the normal MONICA cohort was compared with gender, 5beta-tetrahydrocortisol+5alpha-tetrahydrocortisol/tetrahydrocortisone ratio, and waist to hip (W:H) ratio. When analyzed by allele length (0, 1, or 2 short alleles) for the CA(19) marker, there was a trend toward a higher 5beta-tetrahydrocortisol+5alpha-tetrahydrocortisol/tetrahydrocortisone ratio (P = 0.058) and an increased W:H ratio (2 vs. 0.1 short; P(c) = 0.10) with overrepresentation of short alleles. The opposite was true for the CA(15) locus, with longer alleles at this locus predicting increased 11beta-HSD1 activity, particularly in females. Genotypic data from the ADIGEN case-control population was compared with clinical markers of obesity such as BMI and W:H ratio. There was no significant difference in the distribution of either microsatellite marker between lean and obese groups. Allele distributions were binomial, as seen for the MONICA cohort, and the data were split accordingly (zero, one, or two short alleles). No significant association was seen between grouped alleles and the clinical parameters. No association was observed between HSD11B1 genotype and BMI in either population. These data suggest that 11beta-HSD1 is not a major factor in explaining genetic susceptibility to obesity per se. However, weak associations between HSD11B1 genotype, increased 11beta-HSD1 activity, and W:H ratio suggest that polymorphic variability at the HSD11B1 locus may influence susceptibility to central obesity through enhanced 11beta-HSD1 activity (E to F conversion) in visceral adipose tissue.     

Prevalence of mild apparent mineralocorticoid excess in Mennonites

We have studied an unusual patient with mild low-renin hypertension due to a homozygous mutation in the HSD11B2 gene (PNAS 95:10200-10205, 1998). The patient came from an inbred Mennonite family, and though the mutation identified her as an AME patient, she had a normal birth weight and did not demonstrate the typical features of AME, such as hypokalemic alkalosis, low birth weight, failure to thrive, poor growth, and in many cases nephrocalcinosis. Biochemically, typical patients with AME have abnormal cortisol metabolites and an exceedingly diminished ability to convert [11-3H]cortisol to cortisone. In this patient with mild AME, the conversion of cortisol to cortisone was 58% compared to 0 to 6% in typical AME patients, while the normal conversion is 90 to 95%. Molecular analysis of the HSD11B2 gene of this patient showed a homozygous mutation in codon 227 (P227L). We studied this Mennonite population for the prevalence of the P227L mutation. Our hypothesis was that this mild form of AME would be prevalent in the somewhat inbred Mennonite population to which the patient belongs. Our proposed study was 1) to determine if there are other cases of this mild form of AME, and 2) to establish the heterozygote frequency of the mutation in the Mennonites. RESULTS: We did not detect any additional cases of mild AME. We detected 15 carriers of the P227L mutation out of 445 Mennonites, resulting in a heterozygote frequency of 0.03. CONCLUSION: Since this is an inbred population, the chance of two heterozygotes marrying would be 0.001, which is 1 in 1000 people. This population is known to have large families and therefore the possibility of having an affected child is high. The population consists of 2000 members and we have discovered one affected patient. Thus, there might be one other patient in this population.