[A case of Kearns-Sayre syndrome whose asymptomatic mother had abnormal mitochondria in skeletal muscle]

Abstract

The mode of inheritance of Kearns-Sayre syndrome (KSS) and chronic progressive external ophthalmoplegia (CPEO) have not yet been established, since most cases are sporadic. We studied skeletal muscle pathology and mitochondrial DNA (mtDNA) in a sporadic KSS patient (proband) and examined mitochondrial function of the muscle in his asymptomatic family members. The proband was a 56-year-old male with bilateral ptosis, external ophthalmoplegia, retinal degeneration and cardiac conduction disturbance. Biopsied deltoid muscle showed 9.7% of ragged red fibers without cytochrome oxidase (COX) activity and abnormal mitochondria on electron microscopy. Analysis of muscle mtDNA revealed a 4,977 bp deletion between nt. 8,483 and 13,459. None of the family members had symptoms similar to those of the proband. However, an aerobic exercise test of 15W for 15 minutes with an ergometer induced a marked increase in serum lactate levels in the proband's mother. Histology of her biopsied deltoid muscle showed 0.3% of ragged red fibers without COX activity and morphologically abnormal mitochondria. These findings indicate that the abnormal mitochondria of the proband were transmitted from his asymptomatic mother. This also suggests that some of the sporadic KSS/CPEO cases are inherited one.