In a study of the French diabetic population, the frequency of the Gly40Ser mutation in the GCGR gene was found to be as high as 5%, far exceeding that of other genes.484 An analysis of 64 diabetic children in China suggested that the Gly40Ser mutation in the GCGR gene may be associated with genetic susceptibility to T2D,485 as it disrupts the binding of GCGR to glucagon.486 It is hypothesized that the Gly40Ser mutation in GCGR may contribute to β cell dysfunction and increase the risk of diabetes by disrupting glucagon signaling and decreasing the sensitivity of target tissues to glucagon. Here, GCG is linked to diabetes mellitus.