A family history of diabetes (FHD) is a strong predictor of diabetes risk, yet has rarely been investigated in latent autoimmune diabetes in adults (LADA). This study therefore investigated the risk of LADA and type 2 diabetes (T2D) in relation to FHD, taking into account the type of diabetes in relatives.

Data from a population-based study were used, including incident cases of LADA [glutamic acid decarboxylase antibody (GADA)-positive, n=378] and T2D (GADA-negative, n=1199), and their matched controls (n=1484). First-degree relatives with disease onset at age<40 years and taking insulin treatment were classified as type 1 diabetes (T1D) or, if otherwise, as T2D. Odds ratios (ORs) were adjusted for age, gender, BMI, education and smoking. Cases were genotyped for high- and low-risk HLA genotypes.

Both FHD–T1D (OR: 5.8; 95% CI: 3.2–10.3) and FHD–T2D (OR: 1.9; 95% CI: 1.5–2.5) were associated with an increased risk of LADA, whereas the risk of T2D was associated with FHD–T2D (OR: 2.7; 95% CI: 2.2–3.3), but not FHD–T1D. In LADA patients, FHD–T1D vs FHD–T2D was associated with higher GADA but lower C-peptide levels, lower prevalence of low-risk HLA genotypes (5.0% vs 28.6%, respectively; P=0.038) and a tendency for higher prevalence of high-risk genotypes (90.0% vs 69.1%, respectively; P=0.0576).

The risk of LADA is substantially increased with FHD–T1D but also, albeit significantly less so, with FHD–T2D. This supports the idea of LADA as a mix of both T1D and T2D, but suggests that the genes related to T1D have greater impact. LADA patients with FHD–T1D had more T1D-like features, emphasizing the heterogeneity of LADA.