STUDY OF MITOCHONDRIAL-DNA DEPLETION IN MUSCLE BY SINGLE-FIBER POLYMERASE-CHAIN-REACTION

We studied muscle biopsies from 3 children with a mitochondrial myopat hy characterized histochemically by the presence of ragged-red fibers (RRF) and various numbers of cytochrome c oxidase (COX)-negative fiber s. We quantitated the absolute amounts of total mitochondrial DNA (mtD NA) in isolated normal COX-positive muscle fibers and in COX-negative RRF. There was severe mtDNA depletion in all fibers from the two most severe cases. In the third case mtDNA depletion could not be establish ed with conventional diagnostic tools, but it was documented in single COX-negative fibers; COX-positive fibers showed the same amounts of m tDNA as fibers from aged-matched controls. Our observations indicate t hat mtDNA single-fiber PCR quantitation is a highly sensitive and spec ific method for diagnosing cases with focal mtDNA depletion. This meth od also allows one to correlate amounts of mtDNA with histochemical ph enotypes in individual fibers from patients and age-matched controls, thereby providing important information about the functional role of r esidual mtDNA. (C) 1998 John Wiley & Sons, Inc. Muscle Nerve 21: 1374- 1381, 1998.