The objective of this research is to develop statistical methods to assess whether mitochondrial DNA (mtDNA) mutations are involved in the etiology of disease and to estimate the contribution of mtDNA mutations to the disease. The specific aims are as follow: (1) to propose sampling schemes and test statistics to identify if mtDNA mutations are involved in a disease; to compare the power of the test statistics using different sampling schemes assuming mtDNA mutations are involved in the disease; (2) to study if mtDNA mutations are the primary cause of the disease or nuclear mutations may also be involved in the etiology of the disease; in the later case, study the interaction between mtDNA mutations and nuclear mutations; and (3) to estimate the contribution of mtDNA mutations to the disease. The test methods developed in this study will be evaluated and validated through simulation studies and will be applied to a collection of pedigrees for Leber's hereditary optic neuropathy (LHON), a disease known to be related to mtDNA mutations. The test methods and statistics will be applied to field studies on insulin-dependent diabetes mellitus (IDDM). Continuing collaborations on other complex diseases will be sought during the tenure of this project.