Rare and Atypical Diabetes Network

Inclusion Criteria: The following criteria or phenotypes will be considered for suspecting "atypical" participants: * Type 2 diabetes diagnosed at a time when the individual was prepubertal or non-obese * Mendelian pattern, especially with early onset (\<18 years old) * Syndromic (multiple systems involved) * Lipodystrophic * Extremes of BMI * "Mitochondrial" characteristics (e.g., myopathy, hearing deficits) * Non-progressive * Rapidly progressive ("fulminant") * Low insulin requirements (\<0.5 u/kg/day) * Cyclical hyperglycemia with periods of remission * Lean persons with polycystic ovarian syndrome (PCOS) * History of gestational diabetes (GDM) when lean * Lean insulin-resistant persons * If islet autoantibodies and beta-cell function parameters have been measured (where "A" = islet cell autoantibodies, "B" = beta-cell function): oA-B- (i.e., lacking islet autoimmunity makers and lacking beta cell function) oA-B+ with unprovoked DKA at initial presentation (i.e., lacking islet autoimmune markers, with preserved beta-cell function, but presenting with unprovoked DKA) oA-B+ of very young onset (pre-pubertal) (i.e., lacking islet autoimmune markers, with preserved beta-cell function, but very early onset T2D-like phenotype) Exclusion Criteria: * Those with high likelihood of typical type 1, typical type 2, known monogenic, or other known secondary forms of diabetes * Refusal of consent for genetic testing * Islet autoantibody positive (participants who are islet autoantibody positive but present with additional atypical features i.e. syndromic, strong linear family history of diabetes may not be excluded) * Women who are currently pregnant