[Mitochondrial DNA deletions in Kearns-Sayre syndrome].

INTRODUCTION

Kearns-Sayre syndrome (KSS) is a mitochondrial disorder characterized by progressive external ophthalmoplegia, pigmentary retinopathy, onset before 20 years, and ragged-red fibers on muscle biopsy. KSS has been associated to mitochondrial DNA (mtDNA) mutations. We report neurological manifestations and mtDNA deletions in KSS.

METHODS

Six KSS patients underwent neurological examination, biochemical analysis (muscle enzymes, lactate, cerebrospinal fluid analysis), electromicrography, muscle biopsy (Gomori stain, electronic microscopy), electrocardiogram, echocardiography, MRI/CT scan. MtDNA deletions were studied in blood and muscle samples using Southern blotting and long polymerase chain reaction.

RESULTS

Four males and two females (mean age: 27.7 years; range: 17-42; mean age at onset: 8.2 years) were studied. Initial symptoms were ptosis and gaze restriction, fatigue, exercise intolerance and proximal limb weakness. Syncope and neurosensory hypoacusia were initial symptoms in two patients. All of them presented a unique deletion in the mitochondrial genome, in heteroplasmy, and their size was in the range of 4,420 and 9,437 basis pairs. Three of these deletions are reported for the first time in this article. Most of the deletions are flanked by small direct repeats elements.

CONCLUSIONS

Proximal muscle weakness and fatigue appear frequently in KSS patients during follow up. The syndrome in these patients has been caused by mtDNA deletions.