MITOCHONDRIAL-DNA DOES NOT APPEAR TO INFLUENCE THE CONGENITAL ONSET TYPE OF MYOTONIC-DYSTROPHY

Neither the maternal inheritance pattern nor the early onset of congen ital myotonic dystrophy are fully explained. One possible mechanism is that mitochondrial DNA (mtDNA) mutations might interact with the DM g ene product, producing an earlier onset than would otherwise occur. We have used Southern hybridisation to show that high levels of major re arrangements of mtDNA are not present in muscle of five and in blood o f 35 patients with congenital myotonic dystrophy. We used sequence ana lysis to show that no one particular mtDNA morph appears to cosegregat e with congenital onset. A minor degree of depletion of mtDNA compared with nuclear DNA was present in the muscle of five patients with cong enital Dill, but we propose that this is not the primary cause of the muscle pathology but secondary to it. We have not found evidence that mtDNA is involved in congenital myotonic dystrophy.