Previous MR studies using large European datasets revealed the strong causal effects of overall and abdominal obesity on both the development of type 2 diabetes and glycemic traits (fasting glucose, fasting insulin, and HbA1c).40,41 Although the effect of obesity on HbA1c was relatively small in one study,41 both results supported the assertion that obesity causes type 2 diabetes among Europeans through the deterioration of glycemic control and insulin resistance. Here, INS is linked to obesity due to melanocortin 4 receptor deficiency.