HLA similarities indicate shared genetic risk in 21-hydroxylase autoantibody positive South African and United States Addison's disease

Genetic similarities between patients from the United States and South African (SA) Addison's Disease (AD) strengthen evidence for genetic association. SA-AD (n=73), SA healthy controls (N=78), and US-AD patients (N=83) were genotyped for DQA1, DQB1, DRB1, and HLA-B alleles. Serum was tested for the quantity of 21OH-AA and IFNα-AA at the Barbara Davis Center. Although not as profound as in US-AD, in SA-AD 21OH-AA+subjects the predominantly associated risk haplotypes were DRB1*0301-DQB1*0201 (DR3), DRB1*04xx-DQB1*0302 (DR4), and the combined DR3/4 genotype. DQB1*0302 associated DRB1*04xx haplotypes conferred higher risk than those DRB1*04xx haplotypes associated with other DQB1 alleles. We found negative association in 21OH-AA+SA-AD for DQA1*0201-DQB1*0202 and DQA1*0101-DQB1*0501 vs SA controls, and positive association for DQA1*0401-DQB1*0402 vs US-AD. Apart from the class II DR3 haplotype, HLA-B8 did not have an independent effect; however together DR3 and HLA-B8 conferred the highest risk vs 21OH-AA negative SA-AD and SA-controls. HLA-B7 (often with DR4) conferred novel risk in 21OH-AA+SA-AD vs controls. This study represents the first comparison between South African and United States AD populations utilizing genotyping and serology performed at the same center. SA-AD and US-AD 21OH-AA+patients share common HLA risk haplotypes including DR4 (with HLA-B7) and DR3 (with HLA-B8), strengthening previously described HLA associations and implicating similar genetic etiology.