Leigh Pascoe

CYP11B2 Gene Polymorphisms in Idiopathic Hyperaldosteronism

Primary aldosteronism is characterized by autonomous production of aldosterone and arterial hypertension, and it occurs in 2 principal forms: aldosterone-producing adenoma (APA) and idiopathic hyperaldosteronism (IHA). APA can be cured through removal of the adenoma, whereas IHA leads to hypertension that must be treated with medication. The origin of the autonomous aldosterone production in IHA is poorly understood, but genetic factors may contribute to its cause. To test the hypothesis that variants of the aldosterone synthase gene may contribute to susceptibility to IHA, we compared genotypes at 3 polymorphic sites in the CYP11B2 gene in patients with IHA (n=90) with those found in patients with APA (n=38), in patients with essential hypertension (n=72), and in normotensive individuals (n=102). We observed significant linkage disequilibrium among the 3 polymorphisms with 2 frequent haplotypes in all groups studied. One haplotype (C2R) was found to be increased in frequency in the IHA group (47%) compared with the other groups, which had a similar haplotype frequency (36%). The 3 polymorphisms studied have been implicated in either essential hypertension or excess aldosterone production in previous studies. Because of the strong linkage disequilibrium, the observed results could be due to the action of any 1 of the 3 alleles or to another allele in linkage disequilibrium with them. Our results suggest that variations in the CYP11B2 gene may contribute to dysregulation of aldosterone synthesis and lead to susceptibility to IHA.

Structural analysis and evaluation of the 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2) gene in human essential hypertension

Aim Mutations of the 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2) gene cause the syndrome of apparent mineralocorticoid excess, a rare autosomal recessive form of hypertension. We therefore investigated the question of whether variants of the 11β-HSD2 gene can contribute to genetic susceptibility to essential hypertension. Subjects and methods We performed a linkage study in 162 French hypertensive sibships using the affected sib-pair method on 347 sibling pairs and a polymorphic microsatellite marker that we identified in a 30 kb cosmid clone containing the 11β-HSD2 gene. The coding sequence, introns 2–4 and 350 bp of the 5′-flanking region of the 11β-HSD2 gene were screened for polymorphisms by polymerase chain reaction/single-strand conformation polymorphism, and a single polymorphism, Glu178/Glu (G534A), was identified in exon 3, which did not change the encoded amino acid sequence. A case–control study was conducted on 370 hypertensive subjects with a positive family history of hypertension and 783 French subjects with hypertension with or without a family history of hypertension, compared with 313 normotensive control subjects, all of whom were analyzed for the newly identified bi-allelic polymorphism. Results Statistical analyses using the affected sib-pair method did not show significant linkage between the 11β-HSD2 microsatellite marker and hypertension. Furthermore, no positive association with hypertension was found with the Glu178/Glu (G534A) polymorphism. Conclusion Our data do not suggest that variants of the 11β-HSD2 gene contribute substantially to essential hypertension in Caucasians.

Genetic, Biochemical, and Clinical Studies of Patients With A328V or R213C Mutations in 11βHSD2 Causing Apparent Mineralocorticoid Excess

Apparent mineralocorticoid excess is a recessively inherited hypertensive syndrome caused by mutations in the 11beta-hydroxysteroid dehydrogenase type 2 gene, which encodes the enzyme normally responsible for converting cortisol to inactive cortisone. Failure to convert cortisol to cortisone in mineralocorticoid-sensitive tissues permits cortisol to bind to and activate mineralocorticoid receptors, causing hypervolemic hypertension. Typically, these patients have increased ratios of cortisol to cortisone and of 5alpha- to 5beta-cortisol metabolites in serum and urine. We have studied 3 patients in 2 families with severe, apparent mineralocorticoid excess and other family members in terms of their genetic, biochemical, and clinical parameters, as well as normal controls. Two brothers were homozygous for an A328V mutation and the third patient was homozygous for an R213C mutation in the 11beta-hydroxysteroid dehydrogenase type 2 gene; both mutations caused a marked reduction in the activity of the encoded enzymes in transfection assays. The steroid profiles of the 7 heterozygotes and 2 other family members studied were completely normal. The results of a novel assay used to distinguish 5alpha- and 5beta-tetrahydrometabolites suggest that 5beta-reductase activity is reduced or inhibited in apparent mineralocorticoid excess. In 1 patient undergoing renal dialysis for chronic renal insufficiency, direct control of salt and water balance completely corrected the hypertension, emphasizing the importance of mineralocorticoid action in this syndrome.

Disorders of steroid 11β-hydroxylase isozymes

Steroid 11 beta-hydroxylase activity in the adrenal cortex is required for the synthesis of the major glucocorticoids and mineralocorticoids, but different isozymes mediate this conversion in the zona fasciculata, where cortisol is produced, and the zona glomerulosa, the site of aldosterone synthesis. The isozyme in the latter zone also has 18-hydroxylase and 18-oxidase activities that are required for aldosterone synthesis. Mutations in the genes encoding these isozymes respectively result in defective synthesis of cortisol and aldosterone. Recombinations between the two genes that alter the regulation of the isozyme responsible for aldosterone synthesis cause an inherited form of hypertension, glucocorticoid-suppressible hyperaldosteronism.

Angiotensin-converting enzyme and angiotensinogen gene polymorphisms are non-randomly distributed in oral contraceptive-induced hypertension

Objectives and methods: Oral contraceptives (OC) usage increases serum angiotensinogen levels to three to five times normal and about 5% of these women develop arterial hypertension. The genetic contribution to this susceptibility to OC-induced hypertension is poorly understood. We have analyzed the genotypes of 149 hypertensive and 101 normotensive women using oral contraceptives, for three genetic polymorphisms in genes of the renin–angiotensin system: an insertion/deletion (I/D) in the angiotensin converting enzyme (ACE) gene, the T235M polymorphism of the angiotensinogen gene (AGT) and a point mutation in its promoter. Results After cessation of oral contraception the mean arterial pressures of the hypertensive women were separable into two non-overlapping groups; 88 of the women remained hypertensive and 61 returned to normal blood pressure. Both groups of hypertensive women had a similarly higher frequency of hypertensive relatives than the normotensive women, but were otherwise similar. The 235T allele of AGT was significantly increased in frequency in the 61 oral contraceptive-inducible hypertensive women compared with the controls and the 88 women that remained hypertensive. The ACE I/D genotypes were similarly distributed within the three groups of women, but were distinctly non-random in the oral contraceptive-induced hypertensive women when they were also classified by AGT genotype. Conclusion: This statistical interaction of genotype frequencies suggests that the genetic basis of susceptibility to OC-induced hypertension is complex.