LAUSR

OBJECTIVE To investigate natural course, treatment, and outcomes in familial versus sporadic type 1 diabetes. RESEARCH DESIGN AND METHODS In a population-based study, we compared patients with onset of type 1 diabetes before the age of 20 years who had a first-degree relative with type 1 diabetes (familial diabetes) with patients with type 1 diabetes who had no first-degree relative with type 1 diabetes (sporadic diabetes) at diagnosis and over the first 10 treatment years, using multivariable regression and proportional hazards models. Patients were identified from the Diabetes Prospective Follow-up Registry (DPV) between 1995 and 2018. RESULTS Of 57,371 patients with type 1 diabetes, 53,606 (93.4%) had sporadic diabetes and 3,765 (6.6%) had familial diabetes. Familial diabetes, compared with sporadic diabetes, was associated with younger age (median 7.9 vs. 9.7 years, P < 0.001), lower prevalence of ketoacidosis (11.9% vs. 20.4%, P < 0.001), and lower HbA1c levels (9.7% vs. 11.1%, P < 0.001) at onset and higher prevalence of associated autoimmune disease (16.7% vs. 13.6%, P < 0.001). Over 10 years, patients with familial diabetes, in comparison with sporadic diabetes, more often used insulin pumps (P < 0.001) and had a lower rate of severe hypoglycemia (12.97 vs. 14.44 per 100 patient-years, P < 0.001) but similar HbA1c levels (P ≥ 0.08) and ketoacidosis rates (1.85 vs. 2.06 per 100 patient-years, P = 0.11). In familial and sporadic diabetes, absence of ketoacidosis at onset predicted fewer events of severe hypoglycemia (hazard ratio [HR] 0.67, P < 0.001, and 0.91, P < 0.001, respectively) and of ketoacidosis (HR 0.64, P = 0.007, and 0.66, P < 0.001, respectively) after 10 years. CONCLUSIONS Familial type 1 diabetes, compared with sporadic type 1 diabetes, is characterized by earlier disease manifestation and higher autoimmune comorbidity as well as less metabolic decompensation at onset, likely related to higher disease awareness in affected families, while the course of disease is similar. These findings may have implications for the generalizability of results of diabetes prevention trials from patients with familial type 1 diabetes to patients with sporadic type 1 diabetes.