Test Details: Leigh’s disease is a rare inherited neurometabolic disorder characterized by degeneration of the central nervous system. Disease symptoms first appear between 3 and 24 months and progresses rapidly. The age of onset and the clinical course for disease caused by mitochondrial mutation are variable due to mitochondrial heteroplasmy i.e. concurrent presence of wild type and mutant mitochondria in tissues and cells. The heteroplasmy also underlies the phenotypic variability characteristic of mitochondrial diseases. Further, 100% genotype phenotype correlation is not observed. However mitochondrial diseases generally reflect presence of 70-80% mutant mitochondria in the cells. Pediatric patients with complex neurologic features or multisystem organ involvement and familial history in the maternal lineage are recommended for testing.