<qa>  What is the main cause of diabetes?Hypothesis 1. Diabetes as it occurs in youth derives from a spectrum of etiologic processes, from the insulinopenia of autoimmune type 1 to obesity-related, insulin-resistant type 2 diabetes. A subset of children develop diabetes through a combination of the 2 major etiologic pathways, with autoimmune ß-cell destruction aggravated by the presence of insulin resistance related to genetic susceptibility, obesity andor physical inactivity. A fraction of young patients are unclassifiable at onset due to severe symptomatology and ambiguities in measures of ß-cell function. This poses the research challenge of misclassification of disease, as well as the clinical difficulty of potentially inappropriate treatment ... Since patients are drawn from the city-wide registry, clustering of genetic and behavioral risk factors will be systematically identified without the selection bias inherent in case series and clinic-based studies. 