Alternating hemiplegia of childhood in half-sisters.

We present the family of two girls affected with alternating hemiplegia of childhood who were born to the same mother and different fathers. Previous reports suggested mitochondrial dysfunction as an etiologic mechanism for this disorder. Muscle biopsy, including a measurement of the respiratory chain enzymes, performed in one of the sisters showed no mitochondrial abnormalities. The mode of inheritance is not certain, but an autosomal-dominant gene is most likely.