Histological, enzymatic and mitochondrial DNA studies in patients with Kearns-Sayre syndrome and chronic progressive external ophthalmoplegia.

Kearns-Sayre syndrome has been associated with large heteroplasmic mitochondrial DNA deletions and morphological alterations at the cytological level. We have measured the activities of different respiratory chain complexes in 3 patients presenting mitochondrial DNA deletions and found no close correlation between gene deletions and enzymatic activities. These data, therefore, point out the importance of analyses at the mitochondrial DNA level in such mitochondrial disorders because gross biochemistry may miss any defect.