HLA class II genotyping of African American type 1 diabetic patients reveals associations unique to African haplotypes.

HLA genotyping was performed in African American type 1 diabetic patients (n = 772) and controls (n = 1,641) in the largest study of African Americans and type 1 diabetes reported to date. Cases were from Children's Hospital and Research Center Oakland and from existing collections (Type 1 Diabetes Genetics Consortium [T1DGC], Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications [DCCT/EDIC], and Genetics of Kidneys in Diabetes [GoKinD]). Controls were from the T1DGC and from newborn bloodspot cards. The diversity of HLA DRB1-DQA1-DQB1 haplotypes and genotypes is far greater than that found in Europeans and European Americans. Association analyses replicated many type 1 diabetes risk effects of European-derived haplotypes but also revealed novel effects for African-derived haplotypes. Notably, the African-specific "DR3" haplotype DRB103:02-DQA104:01-DQB104:02 is protective for type 1 diabetes, in contrast to the common and highly-susceptible DR3 DRB103:01-DQA105:01-DQB102:01. Both DRB107:01 and DRB113:03 haplotypes are predisposing when they include DQA103:01-DQB102:01g but are protective with DQA102:01-DQB102:01g. The heterozygous DR4/DR9 genotype, containing the African-derived "DR9" haplotype DRB109:01-DQA103:01-DQB1*02:01g, exhibits extremely high risk (odds ratio = 30.88), approaching that for DR3/DR4 in European populations. Disease risk assessment for African Americans differs greatly from risk assessment in European populations. This has profound implications on risk screening programs and underscores the need for high-resolution genotyping of multiple populations for the rational design of screening programs with tests that will fairly represent the population being screened.