OPA1 and cerebellar ataxia: The minimum prevalence of mitochondrial disease was established through molecular genetics testing for mitochondrial DNA (mtDNA) point mutations and deletions, and nuclear-genetic causes of mitochondrial disease in adults (defined as older than 16 years; SPG7 and OPA1 are included in the ataxia and inherited optic neuropathy sections of this report, respectively).12 Both adults and children were included to establish those at risk of mitochondrial disease.