title: Aldosterone synthase deficiency caused by a homozygous L451F mutation in the CYP11B2 gene.
abstract: Isolated hypoaldosteronism is a rare cause of salt wasting in infancy and may be life-threatening, especially in the newborn infant. In a 3wk-old-boy with hyponatremia and hyperkalemia a GC-MS steroid profile on a spot urinary sample showed no 18-oxygenated steroid metabolites indicative for aldosterone synthase deficiency type I. Sequence analysis of the CYP11B2 gene revealed that the patient was homozygous for a novel missense mutation (L451F) caused by a T to C transition at position c.1351 in exon 8, whereas each non-symptomatic parent possessed only one mutated allele. The mutant cDNA was transiently expressed in a human cell line, HCT116 p53(-/-), and activity of the expressed protein optimized by co-expression of different adrenodoxin species, showing complete aldosterone deficiency with 11-deoxycorticosterone or corticosterone as substrates. The L451F mutation is the first mutation found located immediately adjacent to the highly conserved heme-binding C450 of the cytochrome P450. Computer modeling shows that replacement of leucine by phenylalanine leads to a steric effect in the immediate vicinity of the heme thereby preventing the activity of CYP11B2. Thus, by combining highly sensitive hormone detection in a spot urine sample with expression of the mutated cDNA in cell culture the phenotype of the patient can be correlated with a particular molecular defect.
authors.affiliation: Department of Biochemistry, Saarland University, D-66041 Saarbrücken, Germany.
authors.forename: Huy-Hoang
authors.initials: HH
authors.lastname: Nguyen
authors.forename: Frank
authors.initials: F
authors.lastname: Hannemann
authors.forename: Michaela F
authors.initials: MF
authors.lastname: Hartmann
authors.forename: Stefan A
authors.initials: SA
authors.lastname: Wudy
authors.forename: Rita
authors.initials: R
authors.lastname: Bernhardt
mesh_terms: D000818:Animals; D019556:COS Cells; D002460:Cell Line; D002522:Chlorocebus aethiops; D019405:Cytochrome P-450 CYP11B2 / Q000172:deficiency* / Q000235:genetics*; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D020125:Mutation, Missense; D013256:Steroids / Q000652:urine
chemical_list: D013256:Steroids; D019405:Cytochrome P-450 CYP11B2; C033112:corticosterone methyl oxidase I