Mitochondrial DNA mutations in complex I and tRNA genes in Parkinson's disease

Objective: To identify mitochondrial DNA (mtDNA) mutations that predispose to PD, Background: Mitochondrial complex I activity is deficient in PD, mtDNA mutations may account for the defect, but the specific mutations have not been identified. Methods: Complete sequencing was performed of all mtDNA-encoded complex I and transfer RNA (tRNA) genes in 28 PD patients and 8 control subjects, as well as screening of up to 243 additional PD patients and up to 209 control subjects by restriction digests for selected mutations. Results: In the PD patients, 15 complex I missense mutations and 9 tRNA mutations were identified, After screening additional subjects, rare PD patients were found to carry complex I mutations that altered highly conserved amino acids, However, no significant differences were found in the frequencies of any mutations in PD versus control groups. The authors were unable to confirm previously reported associations of mutations at nucleotide positions (np) 4336, 5460, and 15927/8 with PD, Complex I mutations previously linked to Leber's hereditary optic neuropathy, one of which has been linked to atypical parkinsonism, were not associated with PD, Conclusions: mtDNA mutations with a high mutational burden (present in a high percentage of mtDNA molecules in an individual) in complex I or tRNA genes do not play a major role in the risk of PD in most PD patients. Further investigations are necessary to deter-mine if any of the rare mtDNA mutations identified in PD patients play a role in the pathogenesis of PD in those few cases.