It isn't (entirely) genetic. There are some genes that are risk factors, but no one knows what causes T1D. It also doesn't affect you at birth–it's an autoimmun

It isn't (entirely) genetic. There are some genes that are risk factors, but no one knows what causes T1D. It also doesn't affect you at birth–it's an autoimmune disease that usually manifests between the ages of 3 and 20 but can appear at any time in life (see the other commenter in this thread whose wife developed T1D in her 40s). In keeping with this, the risk factor genes are mostly related to the immune system. Even in populations with the highest risk haplotype, only ~5% develop T1D, and many people without this haplotype also develop T1D. If it were purely genetic, evolution would have selected against these genes long ago since T1D was a terminal disease with a life expectancy of less than a year until the discovery and development of insulin-based therapies in the 1920s.