Somewhat unforeseen, but not necessarily unexpected, the susceptible HLA-DR4 and INS genotypes are associated with altered microbiome compositions during childhood [41, 42], whereas HLA-DR4 is associated with an increased birthweight [43, 44], and the microbiome and birthweight have been reported to be associated with the development of islet autoimmunity and type 1 diabetes [45–50]. Here, INS is linked to type 1 diabetes mellitus.