Selective hypoaldosteronism in Iranian Jews: An autosomal recessive trait

History of Adrenal Research: From Ancient Anatomy to Contemporary Molecular Biology

The adrenal is a small, anatomically unimposing structure that escaped scientific notice until 1564 and whose existence was doubted by many until the 18th century. Adrenal functions were inferred from the adrenal insufficiency syndrome described by Addison and from the obesity and virilization that accompanied many adrenal malignancies, but early physiologists sometimes confused the roles of the cortex and medulla. Medullary epinephrine was the first hormone to be isolated (in 1901), and numerous cortical steroids were isolated between 1930 and 1949. The treatment of arthritis, Addison's disease, and congenital adrenal hyperplasia (CAH) with cortisone in the 1950s revolutionized clinical endocrinology and steroid research. Cases of CAH had been reported in the 19th century, but a defect in 21-hydroxylation in CAH was not identified until 1957. Other forms of CAH, including deficiencies of 3β-hydroxysteroid dehydrogenase, 11β-hydroxylase, and 17α-hydroxylase were defined hormonally in the 1960s. Cytochrome P450 enzymes were described in 1962-1964, and steroid 21-hydroxylation was the first biosynthetic activity associated with a P450. Understanding of the genetic and biochemical bases of these disorders advanced rapidly from 1984 to 2004. The cloning of genes for steroidogenic enzymes and related factors revealed many mutations causing known diseases and facilitated the discovery of new disorders. Genetics and cell biology have replaced steroid chemistry as the key disciplines for understanding and teaching steroidogenesis and its disorders.

Genetic screening in the Persian Jewish community: A pilot study

PURPOSE

Israeli investigators have identified several relatively frequent disorders due to founder point mutations in Persian (Iranian) Jews, who, for nearly three centuries up to the Islamic Revolution of 1979, were completely isolated reproductively.

METHODS

Using a community-based model previously employed with Tay-Sachs disease prevention, we developed a pilot program for the Persian Jewish community of greater Los Angeles. We screened for mutations responsible for four relatively frequent autosomal recessive conditions in Persian Jews in which effective interventions are available for each: Pseudocholinesterase deficiency (butyryl cholinesterase deficiency); Congenital hypoaldosteronism (corticosterone methyl oxidase II); Autoimmune polyendocrinopathy (autoimmune regulatory element); and Hereditary Inclusion Body myopathy.

RESULTS

One thousand individuals volunteered. Mutations were assessed in saliva-derived DNA and were positive for 121/1000 butyryl cholinesterase deficiency; 92/1000 Hereditary Inclusion Body myopathy; 38/1000 corticosterone methyl oxidase II; and 37/1000 autoimmune regulatory element. Ten homozygous individuals (9 butyryl cholinesterase deficiency and 1 Hereditary Inclusion Body myopathy) and 10 "at-risk" couples (seven for butyryl cholinesterase deficiency and one each for the other three disorders) were identified. These frequencies are comparable with those in Israel and indicate an extraordinary level of inbreeding, as anticipated.

CONCLUSIONS

A carefully planned effort can be delivered to an "increased risk" community if detailed attention is given to planning and organization. However, availability of an effective intervention for those found to be "at-risk" or possibly affected, is essential before embarking.

Hereditary disorders among Iranian Jews

Iranian Jews represent an ancient community with a very high degree of inbreeding. Although the community remained relatively isolated, it had strong ties with Babylonian Jewry in Iraq. Several genetic disorders have been reported to be frequent among Iranian Jews, in particular, corticosterone methyloxydase deficiency type II, polyglandular syndrome, and rimmed vacuole myopathy. Based on the data collected in our clinic, recessive and dominant deafness also appear to be frequent. Other diseases, such as beta-thalassemia, achromatopsia, colobomatous microphthalmia, Dubin-Johnson syndrome, and congenital myasthenia gravis, were frequent in both the Iranian and Iraqi Jewish communities. The place of origin of the families within Iran and the results of molecular studies suggest some reason(s) for the high frequency of these disorders among Iranian Jews. While the high frequency of some of the disorders, such as corticosterone methyloxydase deficiency type II, represents a founder effect, in other diseases (such as beta-thalassemia) it was secondary to heterozygote advantage.

Mutations in human 11 beta-hydroxylase genes: 11 beta-hydroxylase deficiency in Jews of Morocco and corticosterone methyl-oxidase II deficiency in Jews of Iran

Steroid 11 beta-hydroxylase is encoded by two homologous genes, CYP11B1 and CYP11B2, located on chromosome 8q21-22. CYP11B1 encodes a specific cytochrome P-450 (P-450c11) necessary for cortisol biosynthesis, with predominantly 11 beta-hydroxylase and moderate 18-hydroxylase activity, whereas CYP11B2 encodes another isozyme (P-450cmo) necessary for aldosterone biosynthesis, with 11 beta-hydroxylase, 18-hydroxylase and 18-oxidase activities (the latter two termed corticosterone methyl-oxidase I and II; CMO-I and II, respectively). Two steroid biosynthetic defects, both relatively frequent in Israel, are caused by specific mutations in each of these genes. 11 beta-Hydroxylase deficiency is frequent among Jews from Morocco (1 in 5000 to 7000 births), and is characterized by virilization, hypertension, impaired cortisol biosynthesis, and increased deoxycorticosterone and androgens. Affected individuals have a single base substitution in exon 8 of CYP11B1, codon 448, from CGC (arginine) to CAC (histidine). This sequence, normally absent in CYP11B2, constitutes a true point mutation within the heme binding domain of CYP11B1 that results in marked impairment of enzymatic activity. The clinical expression is characterized by a wide range of variability in the signs of both androgen and mineralocorticoid excess, even though an identical mutation was found in all but one of the affected alleles examined. CMO-II deficiency is frequent among Jews from Iran (1 in 4000 births), and is characterized by a typical salt-wasting syndrome, increased 18-hydroxycorticosterone, impaired aldosterone biosynthesis, and a high ratio of these steroids. No mutation was found in CYP11B1, but all individuals affected were homozygous for two missense mutations in CYP11B2. The first, in exon 3, codon 181, from CGG (arginine) to TGG (tryptophane) is a mutation that completely abolishes both CMO-I and II activities, whereas the second, in exon 7, codon 386, from GTG (valine) to GCG (alanine) is a more conservative substitution that produces only a minimal reduction in CMO-I activity. Individuals homozygous for either one of these mutations are asymptomatic.

Mutations in the human CYP11B2 (aldosterone synthase) gene causing corticosterone methyloxidase II deficiency

Corticosterone methyloxidase II (CMO-II) deficiency is an autosomal recessive disorder of aldosterone biosynthesis, characterized by an elevated ratio of 18-hydroxycorticosterone to aldosterone in serum. It is genetically linked to the CYP11B1 and CYP11B2 genes that, respectively, encode two cytochrome P450 isozymes, P450XIB1 and P450XIB2. Whereas P450XIB1 only catalyzes hydroxylation at position 11 beta of 11-deoxycorticosterone and 11-deoxycortisol, P450XIB2 catalyzes the synthesis of aldosterone from deoxycorticosterone, a process that successively requires hydroxylation at positions 11 beta and 18 and oxidation at position 18. To determine the molecular genetic basis of CMO-II deficiency, seven kindreds of Iranian-Jewish origin were studied in which members suffered from CMO-II deficiency. No mutations were found in the CYP11B1 genes, but two candidate mutations, R181W and V386A, were found in the CYP11B2 genes. When these mutations were individually introduced into CYP11B2 cDNA and expressed in cultured cells, R181W reduced 18-hydroxylase and abolished 18-oxidase activities but left 11 beta-hydroxylase activity intact, whereas V386A caused a small but consistent reduction in the production of 18-hydroxycorticosterone. All individuals affected with CMO-II deficiency were homozygous for both mutations, whereas eight asymptomatic subjects were homozygous for R181W alone and three were homozygous for V386A alone. These findings confirm that P450XIB2 is the major enzyme mediating oxidation at position 18 in the adrenal and suggest that a small amount of residual activity undetectable in in vitro assays is sufficient to synthesize normal amounts of aldosterone.

Aldosterone deficiency II (CMO II deficiency) is not the result of a mutation of an MspI restriction site within the CYP11B gene

We report our investigations of a German family with aldosterone deficiency (CMO II deficiency). Restriction fragment length polymorphism analysis using a P450c11 probe demonstrates that a MspI restriction site mutation within the CYP11B gene cannot be the underlying cause for this defect, as has been suggested previously.

An inherited defect in aldosterone biosynthesis caused by a mutation in or near the gene for steroid 11-hydroxylase

The final step in aldosterone biosynthesis, an oxidation at position 18 of 18-hydroxycorticosterone, is catalyzed by an enzymatic activity termed corticosterone methyl oxidase II (CMO II). This activity is mediated in vitro by P450c11 (steroid 11-hydroxylase), a cytochrome P-450 enzyme that also catalyzes the preceding two steps of 11-hydroxylation and 18-hydroxylation. CMO II deficiency, an inherited defect in the 18-oxidation step, impairs aldosterone biosynthesis and thus leads to a clinical syndrome of salt wasting. To test the hypothesis that CMO II deficiency results from a mutation affecting the structural gene for P450c11, we examined 11 affected and 21 unaffected members of six families with this disorder. After DNA samples were digested with the restriction endonuclease MspI (thereby cutting the DNA at specific sites) and hybridized with a P450c11 DNA probe, a unique DNA fragment in the P450c11 structural gene was detected in subjects with the deficiency. The DNA fragment and the disease trait were inherited together in each family, demonstrating that CMO II deficiency is caused by a mutation in or very near the structural gene for P450c11 on chromosome 8. We conclude that the metabolic diseases of CMO II and 11-hydroxylase deficiency, which have distinct clinical symptoms, may be caused by different mutations in the single gene for a multifunctional enzyme.

Linkage and segregation analysis of HLA and congenital hypoaldosteronism due to corticosterone methyl-oxydase deficiency type I and type II

To determine the genetic relations between HLA and deficiencies of steroidogenic enzymes other than 21-hydroxylase, we investigated HLA and congenital hypoaldosteronism in two families with corticosterone methyl-oxidase type 2 (CMO2) and one family with type 1 (CMO1) deficiency, respectively. Apart from a first documentation of HLA in CMO1 deficiency, our results, combined with those reported previously, excluded close linkage of HLA and CMO2 deficiency. However, loose linkage could not be encluded and the segregation of HLA haplotypes in sibships with CMO2 deficiency deviated significantly from random segregation. We suggest that HLA and CMO2 deficiency may not be independent.

HLA in a selective aldosterone biosynthetic defect due to type 2 corticosterone methyl-oxidase deficiency

HLA phenotypes were studied in nine Jewish families, originating from Iran, with 18 individuals affected with a selective aldosterone biosynthetic defect and 12 healthy siblings. This disorder is inherited through an autosomal recessive gene and parents were consanguineously related in eight out of nine sibships. Family analysis showed that 18 affected individuals carried 20 different haplotypes and only two patients were homozygous for a haplotype. Yet a peak lod score of 1.128 was obtained for the recombinant fraction of 0.05 and thus linkage to HLA cannot be ruled out.

Genetic polymorphisms among Iranian Jews in Israel

Iranian Jews represent a very ancient Jewish community with a high frequency of inbreeding. A sample of Iranian Jews, mainly unrelated students, was tested for genetic markers of red blood cells and serum. The frequency of glucose-6-phosphate dehydrogenase deficiency was not uniform among Jews who had lived in different areas of Iran; it was lower among those from central Iran (6.7%) than in those from southern and western Iran (16.7% and 20.6%, respectively). The frequencies of B, CDe, cDE, S, and K alleles were among the highest recorded in Jewish ethnic groups. Iranian Jews were similar to Iraqi Jews with respect to the frequencies of the blood markers B, CDe, cde, cDe, ACP, PGM1, ADA, and Hp; however, the B and CDe markers occur with similar frequencies among indigenous Iranians. The presence of the cDe allele and the Gm1,5,13,14,17 haplotype in low frequencies indicates black admixture. Mongoloid admixture is indicated by the polymorphism of the Gm1,13,15,16,17 haplotype. The very rare phenotype Gm(3,5,13,14,17) was observed in 4.8% of 167 individuals tested. This phenotype has not been previously observed among Jews.