Two genes encoding steroid 21-hydroxylase are located near the genes encoding the fourth component of complement in man

P. C. White, D. Grossberger, B. J. Onufer, D. D. Chaplin, M. I. New, B. Dupont, J. L. Strominger

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Two genes encoding steroid 21-hydroxylase [21-OHase; steroid 21-monooxygenase; steroid, hydrogen-donor:oxygen oxidoreductase (21-hydroxylating); Ec], a cytochrome P-450 enzyme, have been located within the HLA major histocompatibility complex. Congenital adrenal hyperplasia due to 21-OHase deficiency is a common inherited disorder of cortisol biosynthesis which is in genetic linkage disequilibrium with certain extended HLA haplotypes. These haplotypes include characteristic serum complement allotypes. A series of cosmid clones was isolated from a human genomic library by using a probe encoding part of the fourth component of complement, C4. These clones also hybridized with a probe encoding most of human 21-OHase. Restriction mapping and hybridization analysis showed that there are two 21-OHase genes, each located near the 3' end of one of the two C4 genes. Hybridization with probes specific for the 5' and 3' ends of the 21-OHase gene showed that the 21-OHase and C4 genes all have the same orientation. The 21-OHase genes 3' to C4A and C4B carry Taq I fragments of 3.2 and 3.7 kilobases (kb), respectively. Both of these fragments are found in genomic DNA of most individuals. In DNA from an individual with the severe, 'salt-wasting' form of 21-OHase deficiency who was homozygous for HLA-A3;Bw47;C4A*1;C4B*Q0(null); DR7, the 3.7-kb Taq I fragment is absent, whereas hormonally normal individuals homozygous for HLA-A1;B8;C4A*Q0; C4B*1;DR3 do not carry the 3.2-kb Taq I fragment. These data suggest that the 21-OHase 'B' gene (3.7-kb Taq I fragment) is functional but the 21-OHase 'A' gene (3.2-kb Taq I fragment) is not.

Original languageEnglish (US)
Pages (from-to)1089-1093
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number4
StatePublished - 1985

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