Mutations in the Human CYP11B2 (Aldosterone Synthase) Gene Causing Corticosterone Methyloxidase II Deficiency

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 89; no. 11; pp. 4996 - 5000
• Main Authors: Pascoe, Leigh, Curnow, Kathleen M., Slutsker, Liliya, Rosler, Ariel, White, Perrin C.
• Format: Journal Article
• Language: English
• Published: Washington, DC National Academy of Sciences of the United States of America 01.06.1992; National Acad Sciences; National Academy of Sciences
• Subjects: Adrenal cortex; Adrenals. Adrenal axis. Renin-angiotensin system (diseases); aldosterone; Base Sequence; Biological and medical sciences; Biosynthesis; Complementary DNA; Corticosterone; corticosterone 18-monooxygenase; COS cells; CYP11B2 gene; Cytochrome P-450 CYP11B2; Cytochrome P-450 Enzyme System - genetics; cytochrome P450XIB2; DNA; Endocrine system; Endocrinopathies; Enzymes; Exons; Genes; Genetic mutation; Genetics; Humans; Iran; Jews; man; Medical disorders; Medical sciences; Metabolism; Mixed Function Oxygenases - deficiency; Molecular Sequence Data; Mutagenesis, Site-Directed; Mutation; Non tumoral diseases. Target tissue resistance. Benign neoplasms; nucleotide sequence; Oligodeoxyribonucleotides - chemistry; Pedigree; RNA; role; Steroid Hydroxylases - genetics; Endocrinopathy; Human; Adrenal glands; Enzyme; Steroid hormone; Isozyme; Mineralocorticoid; Cytochrome P450; Deficiency; Biosynthesis; Aldosterone; Genetic disease; Missense mutation
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.89.11.4996

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 11β of 11-deoxycorticosterone and 11-deoxycortisol, P450XIB2 catalyzes the synthesis of aldosterone from deoxycorticosterone, a process that successively requires hydroxylation at positions 11β 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 11β-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.