Introduction: The phenotype of type 1 diabetes (T1D) has been explored mainly in white populations. People of non-white ethnicity are reportedly less likely to be antibody positive, but phenotypic differences are not well characterised. We investigated ethnic group differences in the clinical characteristics and antibody (Ab) status at clinical onset of T1D.

Methods: We studied people of white European (WE), Asian (A) and black African/Caribbean (AC) ethnicity with clinically-assigned T1D, age ≥5 years, recruited ≤ 6 months after diagnosis, and with Abs (GADA, IA-2A and ZnT8A) measured by radioimmunoassay.

Results: Ethnic breakdown: WE n=1,997, A n=50, AC n=41. Median (IQR) ages were: WE 23(14-24), A 18(12-29), AC 26 (15-41) years p=0.007. Presentation with DKA was more common in AC (65%) than WE (42%) or A (53%) p=0.006; otherwise clinical presentation (polyuria/dipsia, weight loss, fatigue, symptom duration) was similar. Proportions with 0, 1 and ≥2 Abs differed by ethnicity: WE (15%, 24%, 61%); A (28%, 26%, 46%); AC (36%, 32%, 32%) p<0.001. For Ab negative (0 Abs), ethnic groups differed in BMI (p=0.001) and presentation with DKA (<0.001), but other characteristics, including daily insulin dose, were similar. For Ab positive (≥1 Ab), there were differences in parental history of diabetes p=0.02; otherwise ethnicity had no impact. Also, differences were seen in the frequency of IA-2A: WE (67%), A (53%), AC (50%) p=0.03 and ZnT8A: WE (60%), A (39%), AC (42%) p=0.01, but not GADA: WE (83%), A (94%) AC (92%) p=0.09.

Conclusion: Although clinical presentation of T1D was remarkably similar across ethnic groups, variations were found in the proportions with Ab positivity and frequencies of individual Abs. Antibody negativity was more common in non-white ethnic groups and the presence of >1 Ab most common in white ethnicity. Practitioners should be alert to differences in phenotype according to antibody status that may impact classification in some ethnic groups.