Since our laboratory's initial linkage of Type 2 diabetes to a mtDNA rearrangement in a three generation maternal pedigree 13 years ago, there has been increasing support for our hypothesis that mitochondrial dysfunction plays an important role in the etiology of Type 2 Diabetes Mellitus (DM) and the overlapping Metabolic Syndrome (MS). With this study we are planning an extensive investigation of defects in mitochondrial oxidative phosphorylation (OXPHOS) caused potentially by deleterious sequence variants in the mitochondrial DNA (mtDNA). As the primary objective we are trying to further substantiate 2 hypotheses: 1) that these diabetogenic mtDNA variants, which are proposed to range from recent, relatively severe, mutations will result in substantial OXPHOS defects with familial DM & MS and 2) that ancient, relatively mild polymorphisms result in partial OXPHOS defects and an increase in the risk to develop DM & MS.