Metabolic evidence for impaired 17alpha-hydroxylase activity in a kindred bearing the E305G mutation for isolate 17,20-lyase activity.
BACKGROUND
The CYP17A1 gene encodes many enzymatic reactions including 17alpha-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 17alpha-hydroxylase activity which was at odds with subnormal tetracosactrin stimulated cortisol in the patients.


OBJECTIVE
To investigate the in vivo activity of the adrenal enzymes, we used the metabolomics approach with urinary steroid profiling by gas chromatography-mass spectrometry.


METHODS
Of 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.


RESULTS
In the homozygous patients for E305G, both serum and urinary steroids showed a severe lack of androgens (C(19)-steroids) pointing to the absence of 17,20-lyase activities. Furthermore, precursor/product ratios of urinary steroid metabolites characterizing 17alpha-hydroxylase activity showed variable decreases in 17alpha-hydroxylase activities.


CONCLUSIONS
The 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 17alpha-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 17alpha-hydroxylase activity.
Tiosano
Dov
D
Pediatric Endocrinology, Metabolic Biochemistry Laboratory and Genetics Institute, Rambam Medical Center, Meyer Children's Hospital, Technion-Israel Institute of Technology, 9602 Haifa, Israel. d_tiosano@rambam.health.gov.il
Knopf
Carlos
C
Koren
Ilana
I
Levanon
Nurit
N
Hartmann
Michaela F
MF
Hochberg
Ze'ev
Z
Wudy
Stefan A
SA
D000293:Adolescent; D000312:Adrenal Hyperplasia, Congenital / Q000201:enzymology / Q000235:genetics*; D001665:Binding Sites; D002648:Child; D004789:Enzyme Activation; D005192:Family Health; D005260:Female; D008401:Gas Chromatography-Mass Spectrometry; D005837:Genitalia, Male / Q000002:abnormalities; D005838:Genotype; D006579:Heterozygote; D006720:Homozygote; D006801:Humans; D008297:Male; D010375:Pedigree; D017354:Point Mutation; D013254:Steroid 17-alpha-Hydroxylase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D013256:Steroids / Q000652:urine
D013256:Steroids; D013254:Steroid 17-alpha-Hydroxylase