here's the citation for that stat: Parkkola A, Harkonen T, Ryhanen SJ, Ilonen J, Knip M. Extended family history of type 1 diabetes and phenotype and genotype of newly diagnosed children. Diabetes Care 2013; 36(2):348-354. http://www.ncbi.nlm.nih.gov/pubmed/23033245 There are other studies too, but this one also considers 2nd degree relatives. It is from Finland, a high-incidence country. The numbers may be different in a lower incidence country, I don't know. But since genetic risk is thought to partially explain Finland's high incidence rates, I'd guess the familial links would be even higher there than elsewhere. Guessing on that part though!