Compound heterozygous mutations (Arg 239----stop, Pro 342----Thr) in the CYP17 (P45017 alpha) gene lead to ambiguous external genitalia in a male patient with partial combined 17 alpha-hydroxylase/17,20-lyase deficiency.
17 alpha-Hydroxylase deficiency is characterized by defects in either or both the 17 alpha-hydroxylase/17,20-lyase activities. We have, for the first time, elucidated the molecular basis of the deficiency in a male pseudohermaphrodite with ambiguous external genitalia resulting from partial combined deficiency of both activities. The patient is found to be a compound heterozygote, carrying two different inherited mutant alleles in the cytochrome P45017 alpha (CYP17) gene. One allele, from his mother, contains a stop codon (TGA) in place of arginine (CGA) at amino acid position 239 in exon 4. Because this occurs at the N-terminal side of the heme binding sequence, the putative resultant truncated protein is nonfunctional. The second allele, from his father, contains a missense mutation encoding the substitution of proline (CCA) by threonine (ACA) at position 342 in exon 6. Reconstruction of this mutation by site-directed mutagenesis into human P45017 alpha cDNA followed by expression in COS 1 cells leads to the same amount of immunodetectable P45017 alpha protein as found with expression of the normal P45017 alpha cDNA, although both the 17 alpha-hydroxylase and 17,20-lyase activities are found to be reduced to 40-45% of those of the normal enzyme. The presence of ambiguous external genitalia in this 46 XY individual indicates that greater than 20% of the total normal 17,20-lyase activity is required for complete virilization in the male.
Ahlgren
R
R
Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas 75235.
Yanase
T
T
Simpson
E R
ER
Winter
J S
JS
Waterman
M R
MR
D000312:Adrenal Hyperplasia, Congenital; D000446:Aldehyde-Lyases / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D000483:Alleles; D000595:Amino Acid Sequence; D000818:Animals; D001120:Arginine; D001483:Base Sequence; D015139:Blotting, Southern; D002460:Cell Line; D002648:Child; D003577:Cytochrome P-450 Enzyme System / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D004247:DNA / Q000097:blood / Q000235:genetics / Q000302:isolation & purification; D012734:Disorders of Sex Development / Q000201:enzymology / Q000235:genetics*; D006579:Heterozygote; D006801:Humans; D007962:Leukocytes / Q000201:enzymology; D008297:Male; D008969:Molecular Sequence Data; D009154:Mutation; D009838:Oligodeoxyribonucleotides; D016133:Polymerase Chain Reaction; D011392:Proline; D015183:Restriction Mapping; D013254:Steroid 17-alpha-Hydroxylase / Q000235:genetics* / Q000378:metabolism; D013912:Threonine; D014162:Transfection
D009838:Oligodeoxyribonucleotides; D013912:Threonine; D004247:DNA; D003577:Cytochrome P-450 Enzyme System; D001120:Arginine; D011392:Proline; D013254:Steroid 17-alpha-Hydroxylase; D000446:Aldehyde-Lyases