INS and type 2 diabetes mellitus: Type 2 diabetes is a common disease with high heterogeneity.[1,4] Epidemiological studies have demonstrated that underweight or normal-weight T2D (lean T2D) patients tend to develop rapid β-cell failure in the condition of insulin sensitivity and require early insulin treatment.[1,4] Several studies examined the genetic heterogeneity in lean and obese T2D patients in Caucasian populations previously.[10–14,37] These studies indicated that the lean T2D patients were enriched for known T2D risk alleles in comparison with obese T2D patients,[10–14] most of these were related to β-cell function.