Context: Combined 17alpha-hydroxylase/17,20-lyase deficiency is a rare autosomal recessive form of congenital adrenal hyperplasia presenting with hypertension and sexual infantilism. This disorder is caused by defects in P450c17, encoded by the CYP17A1 gene.
Objective: We describe a 14-yr-old female with clinical and hormonal features of 17alpha-hydroxylase/17,20-lyase deficiency and identify and characterize the activities of her CYP17A1 mutations.
Methods: The coding regions of the CYP17A1 gene were amplified by PCR and sequenced. Mutations were recreated in P450c17 cDNA expression vectors; activities in transfected COS-1 cells were assayed by conversion of radiolabeled precursor steroids. One mutant was also expressed in Escherichia coli, and the reduced adsorption spectrum was measured.
Results: The patient carried the previously described mutation R96W and the novel missense mutation H373D. Neither mutant had detectable activity when expressed in COS-1 cells. Membrane preparations from E. coli expressing the H373D mutant vector produced an absorption peak at 420 nm, whereas the wild-type produced a peak at 450 nm, suggesting that the H373D mutation interferes with protein folding.
Conclusion: The novel P450c17 mutation H373D abolished enzyme activity because of protein misfolding. These data indicate an important role for this residue in P450c17 activity.