ALTERED CYP21 GENES IN HLA-HAPLOTYPES ASSOCIATED WITH CONGENITAL ADRENAL-HYPERPLASIA (CAH) - A FAMILY STUDY

Disorders of the CYP21 gene, which is located within the major histoco mpatibility complex on the short arm of chromosome 6, are the leading causes of congenital adrenal hyperplasia (CAH). The coding gene and a highly homologous pseudogene are tandemly arranged with the two genes for the fourth component of complement (C4A and C4B). To analyse the p revalence rates of mutations of the CYP21 genes and the segregation of the CYP2] genes with their corresponding human leucocyte antigen (HLA )-haplotypes, 21 families with one or two children with the severe for m of 21-hydroxylase deficiency were studied. Mutations of the CYP21 ge ne on their corresponding HLA-haplotype were detected by hybridisation of polymerase chain reaction (PCR)-amplified genomic DNA with sequenc e-specific oligonucleotides and solid phase direct sequencing. Our stu dy has shown the following. (1) A single basepair mutation (A-->G or C -->G) within the second intron is the most frequent mutation leading t o impaired 21-hydroxylase activity. This mutation is only detected in HLA-haplotypes associated with the salt-wasting form of CAH. (2) A lar ge deletion of part or all of the CYP21 gene is associated with the HL A-haplotype A3, BW47, C6, DR7, DR53, DQ2 but is also observed in other HLA-haplotypes and can be detected by a simple rapid PCR restriction fragment length polymorphism method. (3) Two alleles of the coding CYP 21 gene differing in a leucine codon within the first exon, (formerly described as a mutation associated with 21-hydroxylase deficiency) hav e been found with an equal distribution in patients with 21-hydroxylas e deficiency, non-disease HLA-haplotypes and the local healthy control s.