Islet autoantibody frequency in relatives of children with type 1 diabetes who have a type 2 diabetes diagnosis

Abstract Aim This study aimed to evaluate characteristics of autoimmunity in individuals who have a type 2 diagnosis and are relatives of children with type 1 diabetes. Methods Pre‐diagnosis samples (median 17 months before onset) from relatives who were later diagnosed with type 2 diabetes were measured for autoantibodies to glutamate decarboxylase 65 (GADA), islet antigen‐2 (IA‐2A), zinc transporter 8 (ZnT8A) and insulin (IAA) as well as the type 1 diabetes genetic risk score (GRS2). Associations between islet autoantibodies, insulin treatment and GRS2 were analysed using Fisher's exact and t ‐tests. Results Among 226 relatives (64% men; mean age at sampling 41 years; mean age 54 years at diagnosis), 32 (14%) were islet autoantibody‐positive for at least one autoantibody more than a decade before diagnosis. Approximately half of these ( n = 15) were treated with insulin. GADA‐positivity was higher in insulin‐treated relatives than in non‐insulin‐treated relatives (12/18 67% vs. 6/18 33%, p < 0.001). IAA‐positivity was observed in 13/32 (41%) of relatives with autoantibodies. GRS2 scores were increased in autoantibody‐positive relatives ( p = 0.032), but there was no clear evidence for a difference according to treatment ( p = 0.072). Conclusion This study highlights the importance of measuring islet autoantibodies, including IAA, in relatives of people with type 1 diabetes to avoid misdiagnosis.