17α-hydroxylase deficiency in a 46,XY individual with a hypoplastic uterus: In vitro functional validation of a...

17α-hydroxylase deficiency (17-OHD) is a rare autosomal recessive disorder caused by CYP17A1 mutations, and patients with a 46,XY karyotype typically lack a uterus. Here we report a 46,XY 17-OHD case presenting with a hypoplastic uterus and a history of left adrenalectomy, and provide the first in vitro functional characterization of the CYP17A1 c.985_987delTACinsAA mutation. The patient underwent clinical, hormonal, imaging, and genetic evaluations. Wild-type and mutant CYP17A1 were overexpressed in HEK293T cells, and protein expression and 17α-hydroxylase activity were assessed by Western blot and 17-OHP ELISA, respectively. The 46,XY patient had a hypoplastic uterus (35 × 14 × 26 mm) and vaginal structure with no visible gonads on imaging, but serum AMH was 10.71 ng/mL, indicating functional testicular tissue. Genetic testing revealed a homozygous CYP17A1 frameshift mutation (c.985_987delTACinsAA, p.Tyr329fsTer90) and a heterozygous POR variant of no diagnostic significance. Previous in silico structural modeling reports predicted that this mutation would cause protein truncation, but direct in vitro evidence has been lacking. In vitro, the mutant protein was truncated (∼45 kDa vs. 57 kDa for wild-type) and showed complete loss of 17α-hydroxylase activity (17-OHP levels comparable to empty vector control, P < 0.01 for wild-type vs. mutant). This study provides the first in vitro functional evidence that c.985_987delTACinsAA causes protein truncation and complete loss of 17α-hydroxylase activity. The presence of a hypoplastic uterus in this 46,XY patient suggests incomplete Müllerian regression, and for 17-OHD patients with a history of unilateral adrenalectomy, glucocorticoid replacement should be carefully titrated.