Epidemiology of Pediatric Mitochondrial Respiratory Chain Disorders in Northwest Spain

Our knowledge of mitochondrial respiratory chain diseases has increased dramatically in recent years, but relatively little information is available about their prevalence and incidence, either in pediatric or adult patients. This study reports incidence and prevalence estimates, and summarizes the clinical, biochemical, histologic, and genetic characteristics of 51 patients age 0-16 years. The overall annual incidence of all mitochondrial respiratory chain diseases was estimated to be 1.43 cases per 10⁵ in the population as a whole, and 2.85 cases per 10⁵ in the under-6 population. The overall prevalence of all mitochondrial respiratory chain diseases was estimated as 7.5 cases per 10⁵ in the under-19 population, and 8.7 cases per 10⁵ in the under-16 population. These incidence and prevalence estimates are higher than in most previous studies of pediatric populations. Estimated prevalences of specific mitochondrial respiratory chain diseases were 2.05 cases per 10⁵ for Leigh syndrome, 0.68 per 10⁵ for mitochondrial deoxyribonucleic acid (mtDNA) deletions and deletions-duplications, 1.59 per 10⁵ for mtDNA depletions, and 0.45 per 10⁵ for mtDNA point mutations. Leigh syndrome was the most frequent clinical syndrome. The estimates of the prevalences of mtDNA deletions, deletions-duplications, and point mutations set forth here are lower than in similar previous studies, whereas the estimate of the prevalence of mtDNA depletions is rather higher. Sixteen of these patients manifested phenotypic syndromes that have not been previously reported in association with mitochondrial respiratory chain diseases.