MELAS syndrome involving a mother and two children.

Three familial cases of MELAS (mitochondrial encephalomyopathy with lactic acidosis and stroke) have been reported. We describe a family with four normal sons and an affected mother, son, and daughter. Although mitochondrial inheritance has been proposed, autosomal and X-linked dominant patterns are also possible. This family also illustrates the variability of expression of MELAS. The proband has the full syndrome, while the mother and daughter manifested less severe findings. All three did not develop symptoms until adulthood.