ContextThe CYP17A1 gene encodes many enzymatic reactions including 17α-hydroxylase and 17,20-lyase activities. Mutations that selectively ablate the 17,20-lyase activity, causing isolated 17,20-lyase deficiency, are exceedingly rare and may belong to the rarest of all disorders of steroidogenesis. We have previously reported an E305G mutation in the active site of CYP17A1 that apparently causes isolated 17,20-lyase deficiency. Expression studies suggested intact 17α-hydroxylase activity which was at odds with subnormal tetracosactrin stimulated cortisol in the patients.ObjectivesTo investigate the in vivo activity of the adrenal enzymes, we used the metabolomics approach with urinary steroid profiling by gas chromatography–mass spectrometry.PatientsOf the 11 subjects investigated, 6 patients in the kindred were found to be homozygous, 4 members were asymptomatic heterozygous, and 1 was homozygous for the wild-type allele.ResultsIn the homozygous patients for E305G, both serum and urinary steroids showed a severe lack of androgens (C19-steroids) pointing to the absence of 17,20-lyase activities. Furthermore, precursor/product ratios of urinary steroid metabolites characterizing 17α-hydroxylase activity showed variable decreases in 17α-hydroxylase activities.ConclusionsThe results confirm the complete absence of 17,20-lyase activity in vivo, as in the in vitro expression studies. On the other hand, in vivo 17α-hydroxylase activity was partially impaired. Thus, the in vivo metabolic data seem to be more sensitive than the expression study and suggests that this mutation also impairs 17α-hydroxylase activity.

The rate of RNASEL 471delAAAG mutation was previously reported to be less than 7% in Ashkenazi prostate cancer patients. It seems plausible that the same mutation may also be involved in breast/ovarian cancer predisposition in Jewish individuals. To evaluate the role of this mutation in cancer predisposition, a total of 1011 individuals including 294 Jewish men with prostate cancer, 61 Ashkenazi women with ovarian cancer and 50 unaffected women, matched for age and ethnicity, were genotyped for sequence anomalies in a single RNASEL gene amplicon using DGGE and sequencing. Additionally, 209 Ashkenazi BRCA1/2 mutation carriers, 205 high-risk non-carriers matched for cancer type and age at diagnosis, and 192 healthy Ashkenazi women were screened, using DHPLC and restriction methods. The 471delAAAG mutation was detected in a single male with prostate cancer (1/294, 0.3%), in two ovarian cancer patients (2/141, 1.4%) and in one of 242 healthy controls (0.41%). An abnormal DHPLC profile identical to the one produced by the 471delAAAG mutation was noted in 23 additional women. The rate of this polymorphism was significantly elevated in high-risk non-carrier women (16/205; 7.8%) than in BRCA1/2 carriers (2/209; 1.0%) and controls (5/192; 2.6%) (chi = 11.670; P < 0.001). Sequence analysis disclosed a silent polymorphism in Valine at codon 118: c.353 C- > T.The 471delAAAG mutation occurs rarely in Israeli prostate and breast/ovarian cancer patients. A silent polymorphism in the RNASEL gene occurs more prevalently in high-risk Ashkenazi breast/ovarian cancer patients without a BRCA1/2 mutation.