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

AIMS : To compare the age at diagnosis and prevalence of islet autoantibody [glutamic acid decarboxylase (65 kDa) 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. METHODS : Participants were recruited from diabetes outpatient departments and autoantibodies to glutamic acid decarboxylase (65 kDa) and islet antigen 2 were measured by enzyme‐linked immunosorbent assay. RESULTS : 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 ± 10.8 years; 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 (≥ 21 years) 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 (65 kDa) 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 (65 kDa) and islet antigen 2 autoantibody positivity was significantly lower in participants diagnosed at age ≥ 21 years (P < 0.001 for both comparisons). CONCLUSIONS : 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 > 20 years in the black compared to white population suggest a difference in the immunological aetiology of type 1 diabetes in these two population groups.