Evidence for frequent gene conversion in the steroid 21-hydroxylase P-450(C21) gene: implications for steroid 21-hydroxylase deficiency

Am J Hum Genet. 1988 Jan;42(1):17-25.


Oligonucleotide probes specific for the deleterious mutations harbored in the P-450(C21)A pseudogene and oligonucleotide probes specific for the corresponding sequences in the B gene were prepared to examine the molecular lesions in the P-450(C21) gene of P-450(C21)-deficient patients. Using these gene-specific probes, we performed Southern blot analyses of genomic DNAs from 11 patients and eight normal individuals. At least one allele of the B gene (the 3.7-kb TaqI fragment) in a patient was inactivated by mutations caused by recombination with the A gene. The A genes in normal individuals and patients seemed to be replaced frequently (i.e., 10/19 individuals) in their 3' portions by B gene sequences. All of these alterations occurred without changing the characteristic length (3.2 kb) of the TaqI fragment of the A gene, a result strongly suggesting that frequent gene conversions and/or intragenic recombinations have happened in the P-450(C21) genes. Densitometric analysis of the autoradiograms from hybridization experiments revealed extensive variation (from one to five copies) in the copy number of the A gene (the 3.2-kb TaqI fragment) whereas that of the B gene (the 3.7-kb TaqI fragment) was relatively constant at two or three copies.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adrenal Hyperplasia, Congenital
  • DNA / genetics
  • DNA Restriction Enzymes
  • Female
  • Gene Conversion*
  • Humans
  • Male
  • Mutation
  • Nucleic Acid Hybridization
  • Oligonucleotides
  • Pseudogenes*
  • Recombination, Genetic
  • Steroid 21-Hydroxylase / genetics*
  • Steroid Hydroxylases / genetics*


  • Oligonucleotides
  • DNA
  • Steroid Hydroxylases
  • Steroid 21-Hydroxylase
  • DNA Restriction Enzymes