Identification of a subgroup of black South Africans with type 1 diabetes who are older at diagnosis but have lower levels of glutamic acid decarboxylase and islet antigen 2 autoantibodies.

Abstract

To compare the age at diagnosis and prevalence of islet autoantibody [glutamic acid decarboxylase (65kDa) 65 and islet antigen 2] positivity in black and white participants with type 1 diabetes in South Africa, and to analyse the relationship between age at diagnosis and the presence of autoantibodies. Participants were recruited from diabetes outpatient departments and autoantibodies to glutamic acid decarboxylase (65kDa) and islet antigen 2 were measured by enzyme-linked immunosorbent assay. We recruited 472 (353 black and 119 white) participants with type 1 diabetes. Age at diagnosis of diabetes was later in black (19.7±10.5) than in white participants (12.7±10.8years; P<0.001) with a median (interquartile range) disease duration of 5.0 (2.0-10.0) and 8.5 (4.0-20.0) years (P<0.001), respectively. An older age at diagnosis (≥21years) was more frequent in black (152 of 340, 45%) than in white participants (24 of 116, 21%; P<0.001). The prevalence of islet antigen 2 autoantibodies was 19% (66/352) in black and 41% in white participants (48/118; P<0.001). There was no significant difference in glutamic acid decarboxylase (65kDa) autoantibody positivity between black (212/353, 60%) and white participants (77/117, 66%; P=0.269). In black, but not white, participants the prevalence of both glutamic acid decarboxylase (65kDa) and islet antigen 2 autoantibody positivity was significantly lower in participants diagnosed at age≥21years (P<0.001 for both comparisons). The older age at diagnosis, lower prevalence of islet antigen 2 autoantibodies and a distinct subgroup of participants with type 1 diabetes with age at diagnosis of >20years in the black compared to white population suggest a difference in the immunological aetiology of type 1 diabetes in these two population groups.