Mitochondrial DNA abnormalities in skeletal muscle of patients with sporadic amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis is a neurodegenerative disease affecting the anterior horn cells of the spinal cord and cortical motor neurons. Previous findings have suggested a specific impairment of mitochondrial function in skeletal muscle of at least a limited number of patients. Applying flavopr otein/NAD(P)H autofluorescence imaging of mitochondrial function in saponin -permeabilized muscle fibres, we detected a heterogeneous distribution of t he respiratory chain defect among individual fibres in muscle biopsies of p atients (11 out of 17) with sporadic amyotrophic lateral sclerosis (SALS), These findings correlate with the presence of cytochrome c oxidase (COX)-ne gative muscle fibres detected histologically. We established the molecular basis for the decreased activities of NADH:CoQ oxidoreductase and COX in SA LS muscle. In the skeletal muscle of the investigated patients, diminished levels (13 out of 17) or multiple deletions (one out of 17) of mitochondria l DNA (mtDNA) mere observed. These alterations of mtDNA seem to be related to decreased levels of membrane-associated mitochondrial Mn-superoxide dism utase, Our results support the viewpoint that an oxygen radical-induced imp airment of mtDNA is of pathophysiological significance in the aetiology of at least a subgroup of patients with SALS.