MONOZYGOTIC TWINS WITH MELAS-LIKE SYNDROME LACKING RAGGED-RED FIBERS AND LACTACIDEMIA

Typical cases of MELAS present a combination of clinical and neuroradi ological features, lactacidaemia, and ragged red fibers (RRFs) in stri ated muscle. We have observed a MELAS-like syndrome in monozygotic twi ns. They developed seizures typically in conjunction with physical exe rtion, sleep deprivation or febrile episodes. Stroke-like episodes occ urred usually during seizures. In twin 2 the course was fatal at age 2 0 years. Neuroradiological findings were typical of MELAS. Plasma lact ate was normal in both. CSF lactate was normal in twin 1 and normal/el evated in twin 2. RRFs were not seen in muscle biopsies of the twins. Complex I activity was reduced in muscle in twin 1. Brain tissue remov ed at epilepsy surgery in twin 2 showed the presence of mitochondrial angiopathy. The commonest mitochondrial DNA mutation in MELAS, at base pair 3243, was absent. Lactacidaemia and mitochondrial myopathy with RRFs constitute part of the diagnostic criteria of MELAS. However, the absence of these features does not exclude mitochondrial disorder wit h the serious manifestations of MELAS (seizures and stroke-like episod es) as seen in these twins.