Mutation R96W in cytochrome P450c17 gene causes combined 17 alpha-hydroxylase/17-20-lyase deficiency in two French Canadian patients.

Abstract

Congenital adrenal hyperplasia (CAH) is the most frequent cause of adrenal insufficiency and ambiguous genitalia in newborn children. In contrast to CAH caused by 21 alpha-hydroxylase and 11 beta-hydroxylase deficiencies, which impairs steroid formation in the adrenal exclusively, 17 alpha-hydroxylase/17,20-lyase deficiency impairs steroid biosynthesis in the adrenals and gonads. The sequence of CYP17 gene was determined by direct sequencing of asymmetric PCR products in two French-Canadian 46,XY pseudohermaphrodite siblings suffering from combined 17 alpha-hydroxylase/17,20-lyase deficiency. The two patients are homozygous for the novel missense mutation R96W caused by a C to T transition converting codon Arg96 (CGG) into a Trp (TGG) in exon 1. The both parents are heterozygous for this missense mutation. We assessed the effect of the R96W mutation on 17 alpha-hydroxylase/17,20-lyase activity by analysis of mutant enzyme, generated by site-directed mutagenesis, expressed in COS-1 cells. The presence of R96W substitution almost completely abolished the activity of the mutant protein. The present findings provide a molecular explanation for the signs and symptoms of combined 17 alpha-hydroxylase/17,20-lyase deficiency in these two patients and provide useful information on the structure-activity relationships of the P450c17, enzyme.

Combined 17α-hydroxylase/17,20-lyase deficiency due to p.R96W mutation in the CYP17 gene in a Brazilian patient

“…The p.R96W mutation has been reported rarely in CYP17: in two 46,XY DSD French-Canadian siblings presenting with combined 17α-hydroxylase/17,20-lyase deficiency (12), an Italian patient (13) and also in another Brazilian patient (14). Our 16-year old patient sought treatment for delayed puberty and during clinical examination her blood pressure levels were elevated.…”

“…Recently a patient was described who carried both p.R96W and missense H373D mutation on the CYP17 gene, showing that these mutations cause a dramatic loss of both enzymatic P450c17 activities (20). The missense p.R96W mutation causes a transition C→ T in codon Arg 96 (CGG) into a Trp (TGG) in exon 1 (12) (Figure 1), abolishing almost completely the activity of the mutant protein (3,20).…”

“…Subsequently, the patient was started on transdermic estradiol (25 mcg/day) with no interference with blood pressure control. (12). Identified mutations were confirmed by sequencing the product of a second PCR amplification in the opposite direction ( Figure 1).…”

New Compound Heterozygous Mutation in the <i>CYP17</i> Gene in a 46,XY Girl with 17α-Hydroxylase/17,20-Lyase Deficiency

“…The gene for this enzyme (CYP17) is located on chromosome 10q24.3 [2], and mutations in the CYP17 gene have been reported to cause 17α-hydroxylase/17,20-lyase deficiency [3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23]. Adrenal 17α-hydroxylase deficiency is characterized by impaired production of cortisol and compensated hypersecretion of adrenocorticotropin, which stimulates the synthesis of large amounts of 11-deoxycorticosterone and corticosterone, leading to hypertension, hypokalemia, and a suppressed renin-angiotensin system.…”

A 5′-Splice Site Mutation in the Cytochrome P450 Steroid 17α-Hydroxylase Gene in 17α-Hydroxylase Deficiency

“…To date, 20 deleterious mutations have been reported in this disorder (5)(6)(7)(8). These mutations occur in 7 exons of the gene, excluding exon 7, and consist of missense and nonsense mutations as well as small insertions or deletions that alter the reading frame of the gene.…”