The incidence of mitochondrial encephalomyopathies in childhood: Clinical features and morphological, biochemical, and DNA abnormalities

In this study we present incidence, point prevalence, and mortality figures of mitochondrial encephalomyopathies in a population-based study of childr en from western Sweden. Through the screening of registers and review of me dical records, we identified 32 patients under 16 years of age from the stu dy population who were diagnosed between January 1, 1984, and December 31, 1998. The incidence of mitochondrial encephalomyopathies in preschool child ren (<6 years of age) was 1 out of 11,000. The preschool incidence of Leigh 's syndrome was 1 out of 32,000, and the preschool incidences of both Alper 's syndrome and infantile mitochondrial myopathy with cytochrome C oxidase deficiency were 1 out of 51,000. The point prevalence (January 1, 1999) of mitochondrial encephalomyopathies in children under 16 years of age was 1 o ut of 21,000. The median survival for patients with infantile onset was unt il 12 years of age. We identified 4 cases with mitochondrial DNA point muta tions, 2 cases with mitochondrial DNA deletions, and 2 cases with nuclear m utations in the SURF1 gene. We conclude that mitochondrial encephalomyopath ies are relatively common neurometabolic disorders in childhood.