Human complex I defects in neurodegenerative diseases.

Complex I deficiency, either specific or associated with other respiratory chain defects, has been identified in myopathies, encephalomyopathies and in three 'neurodegenerative' disorders: Parkinson's disease, dystonia and Leber's hereditary optic neuropathy. The complex I defect is expressed in blood in all these three but, to date, only in LHON have specific mitochondrial DNA mutations been identified. Recent work with rho degrees cybrids indicates that, in a subgroup of patients at least, the complex I deficiency is determined by mtDNA, in contrast to dystonia where a nuclear gene defect or toxic influence appears a more likely cause. The actions of specific toxins, e.g., MPTP continue to play an important role in our understanding of pathogenesis of neurodegeneration, particularly in PD.