Duplication and deletion of 21 hydroxylase gene among the normal Korean subjects and in adrenogenital syndrome patients

ABSTRACT

Steroid 21 hydroxylase deficiency is a major cause of congenital adrenal hyperplasia(CAH) and is caused by genetic impairment (CYP21B) of this enzyme. In the human genome, CYP21B is located within MHC class III region on the short arm of chromosome 6. Most of the genes in this region are highly polymorphic and crowded. Also the CYP21B gene is accompanied by its pseudogene (CYP21A) and tandemly arranged with two genes of fourth component of complement. This highly complex gene arrangement in this area may predispose genetic unstability of CYP21 genes,i.e. mutations. In the current study, we tried to investigate the frequency of duplication and deletion of CYP21 genes and pattern of the genetic alteration of these genes by RFLPs. We also compared the genetic alteration of CYP21 in normal subjects with those of the CAH patients. According to our study, 15% of the normal Korean population have duplication or deletion of CYP21. There was one normal subject with heterozygous deletion of CYP21B gene. Of the 5 CAH patients examined, we found abnormal patterns in 2 patients. One was a large scale gene conversion and the other was a deletion of CYP21B and C4 locus II genes with gene conversion. These results suggest that high frequency of duplication and deletion of CYP21 and C4 in the general population may provide the genetic pool of instable CYP21 genes and these duplicated or deleted genes may result in gene conversions between CYP21A(pseudogene) and CYP21B(true gene) by preventing the normal recombination event.