Adult-onset type 1 diabetes mellitus (T1DM) remains less well characterized than childhood-onset disease and is often misclassified as type 2 diabetes mellitus (T2DM), particularly after 40 years of age. A retrospective analysis published in Diabetes Care evaluated differences in clinical presentation, islet autoantibody profiles, and human leukocyte antigen (HLA) genetics between adult- and pediatric-onset T1DM.

The analysis included 2,414 individuals with newly diagnosed T1DM, comprising 414 adults aged 20 to 76 years and 2,000 children. Adults had a mean body mass index (BMI) of 23.5 ± 4.7 kg/m² at onset. Islet autoantibodies against glutamic acid decarboxylase (GAD), insulin, islet antigen 2 (IA-2), and zinc transporter 8 (ZnT8) were measured within 1 year of diagnosis using fluid-phase radiobinding assays. High-resolution HLA class I (n=655) and class II (n=1,196) typing was performed in a subset.

Adults presented with diabetic ketoacidosis (DKA) less frequently than children (32.6% vs 56.0%; P<0.001) and had lower glycated hemoglobin (HbA1c) levels at diagnosis (11.3% ± 2.6% vs 12.0% ± 2.4%; P<0.001). Among adults older than 40 years (n=84), DKA was observed in 13.1% of cases.

Adults more often had zero or one islet autoantibody compared with children (43.0% vs 20.2%; P<0.001). The frequency of high-risk HLA haplotypes did not differ significantly between groups, including DR4-DQ8 (57.1% vs 63.7%; P=0.060) and DR3-DQ2 (43.6% vs 46.1%; P=0.482).

These findings indicate that adult-onset T1DM is associated with lower DKA frequency and fewer detectable autoantibodies, while genetic risk patterns remain comparable to those in children. These differences may affect recognition and classification in adult populations.