Over the past years much has been clarified about mitochondrial pathology. There are several encephalomyopathies related to mitochondrial dysfunction, of which the most important are Kearns-Sayre syndrome (KSS), myoclonus epilepsy and ragged red fibres syndrome (MERRF) as well as the mitochondrial encephalomyopathy lactic acidosis and stroke-like episodes syndrome (MELAS), about which several reviews were published recently.1-3

The clinical picture of MELAS is the result of a respiratory chain defect and involves mainly the CNS and the skeletal muscles, which are especially vulnerable to mitochondrial dysfunction because of their dependency on the oxidative metabolism.4 5 The histopathological presentation in the skeletal muscles is ragged red fibres which are caused by impaired intramitochondrial protein synthesis. The clinical expression of MELAS is highly variable, in that different mutations can lead to a similar clinical syndrome and a given mutation may be responsible for an inconstant phenotypical expression.6 7 In most cases, the enzymatic defect in MELAS is a complex I deficiency and, to a lesser degree, a complex IV deficiency. The enzyme abnormality is associated with a point mutation at np3243 in the tRNA Leu(UUR) region, which accounts for 80% of the patients with MELAS.5

The MELAS syndrome was first described in 1984 by Pavlakis et al.8 Later, Hirano and Pavakis7described the target symptoms and additional clinical manifestations, based on 110 reported patients with MELAS. The six target symptoms include clinical stroke, seizures, lactic acidosis, ragged red fibres, exercise intolerance, and onset of symptoms before the age of 40. Additional clinical manifestations comprise dementia, limb weakness, short stature, hearing loss, and recurrent migraine-like headaches. Lactic acidosis is the most common finding from laboratory investigations. …