short PR interval on monitoring duringanaesthesia for tonsillectomy. Subsequenttwelve-lead electrocardiograms (Fig 1) showedWolff-Parkinson-White syndrome with delta wavesseen best in leads I, II, and V3–V5, and a broadQRS complex. This was confirmed by electrophy-siologic study, during which a left lateral accessorypathway with rapid antegrade conduction, down toa cycle length of 170milliseconds, was successfullycatheter ablated (arrow).At the age of 12 years, the patient experiencedthe onset of headache, vomiting, impaired visualacuity, and recurrent focal seizures. Blood and cere-brospinal fluid lactate were increased at 5.6millimolesper litres with a reference unit of 1.0–2.6millimolesper litres and 3.7millimoles per litres with a referenceunit of 0.9–2.2millimoles per litres, respectively.Electroencephalogram showed epileptic discharges onthe left occipital region, while magnetic resonanceimaging of the brain revealed localised T2-hyper-intensity of the left occipital cortex and cerebellaratrophy. The echocardiogram (Fig 2) in the parasternallong (a) and short (b) axis views demonstrated, for thefirst time, concentric left ventricular hypertrophy(arrows). The left ventricular posterior wall measured11 millimetres – the upper limit of normal was 8millimetres – and the ventricular function was normal,without outflow obstruction. MELAS syndrome(mitochondrial myopathy, encephalopathy, lacticacidosis, and stroke-like episodes) was suspected, andthe diagnostic A3243G mutation in mitochondrial