Novel P450c17 mutation H373D causing combined 17alpha-hydroxylase/17,20-lyase deficiency.
BACKGROUND
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.


CONCLUSIONS
The novel P450c17 mutation H373D abolished enzyme activity because of protein misfolding. These data indicate an important role for this residue in P450c17 activity.
Sahakitrungruang
Taninee
T
University of California-San Francisco, San Francisco, CA 94143-0978, USA.
Tee
Meng Kian
MK
Speiser
Phyllis W
PW
Miller
Walter L
WL
D000293:Adolescent; D000312:Adrenal Hyperplasia, Congenital / Q000235:genetics*; D005260:Female; D006801:Humans; D009154:Mutation; D013254:Steroid 17-alpha-Hydroxylase / Q000737:chemistry / Q000235:genetics*
D013254:Steroid 17-alpha-Hydroxylase