A risk-decreasing effect on type 2 diabetes of raised PON-3 levels using the inverse variance-weighted method (p = 3.0 × 104) was cast in doubt by evidence of heterogeneity (p = 3.1 × 10−2) and horizontal pleiotropy in MR Egger (p = 0.033). This evidence concerns the gene PON3 and type 2 diabetes mellitus.