Genetic linkage studies between congenital adrenal hyperplasia and the HLA blood group system

Seventeen families with one or two children suffering from congenital adrenal hyperplasia (CAH) were not only typed for their HLA-A,B, and D antigens but also tested biochemically forCAH heterozygosity after ACTH stimulation. The lod score analysis showed a close genetic linkage betweenCAH andHLA, indicating that theC-21-hydroxylase deficiency gene(s) causing CAH in the homozygous deficient state are-located in close proximity to theHLA complex on chromosome 6 with an estimated recombination fraction of 0 to 5%. HLA typing in 21 unrelated CAH patients revealed a statistically significant association to the HLA-B5 antigen with a relative risk value of 5.8. There was a significant correlation (P=0.0025) between theHLA segregation data and theCAH heterozygosity test results in relatives of CAH patients although a few ‘false negative’ results in theCAH heterozygosity test were observed. Thus, the combination of HLA typing and this biochemical test at present provides the most precise approach for detecting CAH carriers in families of CAH patients.