A patient with mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS) was studied with serial diffusion-weighted MRI (DWI) after stroke-like episodes and the apparent diffusion coefficient (ADC) was measured in an infarct-like lesion. In the acute and subacute stages, the affected area gave high signal on DWI and its ADC was much lower than that in a normal control region. In the chronic stage, the ADC became higher than that in normal brain. We therefore suggest that the stroke-like episodes did not cause vasogenic oedema but were related to energy failure and cytotoxic oedema.

Leigh syndrome is the most common mitochondrial disorder in children characterized by necrotic lesions in the central nervous system. Both mitochondrial DNA (mtDNA) and nuclear DNA defects in the mitochondrial respiratory chain can lead to this disease. To characterize the clinical and genetic traits of Leigh or Leigh-like syndrome patients in China, 124 unrelated cases were collected between 1992 and 2005. Seventy-seven cases (62.1%) met the typical criteria of Leigh syndrome, including symmetrical bilateral abnormal signals in the basal ganglia, thalamus and brain stem, etc. Other cases (37.9%) belonged to Leigh-like syndrome with atypical clinical or radiological manifestations. Late-onset patients accounted for 20.2%, which is more than previously reported. Movement disorder was the most common symptoms in our patients. Thirty-two patients (25.8%) were confirmed to carry mutant genes. Among them, six cases (4.8%) have been demonstrated to have point mutations in mitochondrial DNA. Two separate patients were detected to have mutations on A8344G and A3243G. The T8993G point mutation was identified in one patient and T8993C in one other patient. SURF1 mutations associated with cytochrome-c oxidase deficiency were identified in 25 patients (20.2%). Four unreported variations have been identified in SURF1 gene from three patients. G604C was found in 22 patients. Only one patient had C214T mutation in the pyruvate dehydrogenase E1alpha subunit gene. In the remaining 92 patients (74.2%), a specific molecular dysfunction or underlying metabolic abnormality could not be identified.

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