Widespread tissue distribution of multiple mitochondrial DNA deletions in familial mitochondrial myopathy.

We used Southern blot analysis and the polymerase chain reaction to analyze the tissue distribution of multiple mitochondrial DNA (mtDNA) deletions in a 45-year-old man with familial mitochondrial myopathy-Southern blots showed two major types of abnormal mtDNA with approximately 4- and 8-kilobase deletions in the skeletal and extraocular muscles. The amount of muscle mtDNA with deletions correlated approximately with the severity of muscle involvement. The polymerase chain reaction showed multiple mtDNA deletions even in clinically asymptomatic tissues, the pattern of which differed with the type of tissue. Nucleotide sequences of several mtDNAs with deletions showed that the deletions were flanked by direct repeats consisting of 3 to 12 nucleotides. Leukocytes from the patient's affected sister and his mother exhibited the same mtDNA deletion pattern. Most of the same deletions were present in leukocytes obtained from the patient's father.