Molecular basis of apparent isolated 17,20-lyase deficiency: compound heterozygous mutations in the C-terminal region (Arg(496)----Cys, Gln(461)----Stop) actually cause combined 17 alpha-hydroxylase/17,20-lyase deficiency.
The molecular defect in a reported case of isolated 17,20-lyase deficiency in a 46XY individual has been elucidated. The patient was found to be a compound heterozygote, carrying two different mutant alleles in the CYP17 gene. One allele contains a point mutation of arginine (CGC) to cysteine (TGC) at amino acid 496 in exon 8. The second allele contains a stop codon (TAG) in place of glutamine (CAG) at position 461 in exon 8 which is located 19 amino acids to the carboxy-terminal side of the P-450(17) alpha heme binding cysteine. COS-1 cells transfected with cDNAs containing one or the other of these mutations showed dramatically reduced 17 alpha-hydroxylase and 17,20-lyase activities relative to cells transfected with the wild type P-450(17) alpha cDNA. While the in vitro data in COS 1 cells can explain the patient's physical phenotype, with female external genitalia, it was somewhat discordant with the clinical expression of isolated 17,20-lyase deficiency with relative preservation of 17 alpha-hydroxylase activity in vivo. In addition to the expression studies of these two examples of mutants in the C-terminal region of cytochrome P-450(17) alpha, a third mutant cDNA construct containing a 4-base duplication at codon 480 previously found in patients with combined 17 alpha-hydroxylase/17,20-lyase deficiency was also expressed in COS-1 cells. This expressed protein was completely inactive with respect to both activities, supporting the biochemical findings in serum and in vitro biochemical data obtained using a testis from the patient. The results from these patients clearly indicate the importance of the C-terminal region of human P-450(17) alpha in its enzymatic activities.
Yanase
T
T
Department of Biochemistry and Obstetrics and Gynecology, University of Texas Southwestern Medical Center, Dallas 75235.
Waterman
M R
MR
Zachmann
M
M
Winter
J S
JS
Simpson
E R
ER
Kagimoto
M
M
D000293:Adolescent; D000312:Adrenal Hyperplasia, Congenital; D000446:Aldehyde-Lyases / Q000172:deficiency / Q000235:genetics*; D000595:Amino Acid Sequence; D001483:Base Sequence; D002460:Cell Line; D003577:Cytochrome P-450 Enzyme System / Q000172:deficiency / Q000235:genetics*; D012734:Disorders of Sex Development / Q000201:enzymology / Q000235:genetics*; D006579:Heterozygote; D006801:Humans; D008297:Male; D008969:Molecular Sequence Data; D009154:Mutation; D014162:Transfection
D003577:Cytochrome P-450 Enzyme System; D000446:Aldehyde-Lyases