A mitochondrial disease with characteristics of cataracts, hypertrophic cardiomyopathy, muscle weakness and lactic acidosis after exercise. May present in two forms, a neonatal lethal form or a chronic form. Hypertrophic cardiomyopathy is diagnosed at birth in half of the patients in both forms. Approximately half of the patients die within the first year of life due to cardiac failure. Nystagmus, strabismus, hypotonia, hyporeflexia and delayed motor development are occasional features. Those who survive the neonatal period and infancy manifest the chronic form with stable cardiomyopathy and myopathy and have a normal intellect. Physical mobility is impaired due to muscular weakness in most patients. In the majority of cases, mutations (nonsense, frame-shift, start codon or splice site) in the AGK gene have been identified. The reported mutations are transmitted in an autosomal recessive manner.