DELETION OF AMINO-ACIDS ASP (487)-SER(488)-PHE(489) IN HUMAN CYTOCHROME P450C17 CAUSES SEVERE 17-ALPHA-HYDROXYLASE DEFICIENCY

17alpha-Hydroxylase deficiency blocks the biosynthesis of cortisol and sex steroids, resulting in mineralocorticoid excess, hypertension, sexual infantilism, and female phenotype in both genetic sexes. The disease is caused by mutations in the gene encoding cytochrome P450c17, which is the single enzyme that mediates both 17alpha-hydroxylase and 17,20-lyase activities. We report a 14-yr-old patient from Thailand with a classical clinical presentation of this rare disorder. Analysis of her P450c17 gene by polymerase chain reaction amplification and sequencing showed a nine-base deletion, eliminating codons 487-489 (Asp-Ser-Phe) near the carboxy-terminus of P450c17. This deletion creates a BclI site in the mutant DNA, permitting accurate demonstration that the patient was homozygous for this lesion, whereas one parent and two siblings were heterozygous. By use of site-directed mutagenesis, we created a vector that could express this mutated form of P450c17 when transfected into non-steroidogenic COS-1 cells. Such transfected cells produced immunodetectable P450c17 protein, but had no 17alpha-hydroxylase or 17,20-lyase activity, whereas cells similarly transfected with a vector expressing normal human P450c17 could 17alpha-hydroxylate either pregnenolone or progesterone and convert 17alpha-hydroxypregnenolone to dehydroepiandrosterone, showing the presence of both activities. This is the first report of the molecular genetic basis of 17alpha-hydroxylase deficiency in a Southeast Asian patient.