[Letter] Primary mitochondrial diseases increase susceptibility to bipolar affective disorder

Introduction Primary mitochondrial diseases (PMD) are heterogeneous disorders caused by mutations in nuclear DNA-encoded and mitochondrial DNA (mtDNA)-encoded genes. Neurological impairment is common and reflects the susceptibility of the central nervous system to alterations in mitochondrial oxidative metabolism. Case reports and small-scale cross-sectional studies in PMD have suggested a high comorbidity with neuropsychiatric syndromes, including mood disorders (online supplementary table 1).1 However, the prevalence of affective syndromes in a large cohort of patients with PMD has not been systematically evaluated. The putative link between mitochondria and mood psychopathology is further strengthened by converging evidence that implicates mitochondrial dysfunction in bipolar affective disorder (BPAD) syndromes.2 3 BPAD affects approximately 1% to 4% of the population worldwide;4 Type I is diagnosed on the basis of =1 lifetime occurrence of mania, while Type II is characterised by episodes of depression and hypomania. We present a large-scale cross-sectional cohort study of the prevalence of BPAD and other affective syndromes, including major depressive episode (MDE) and generalised anxiety disorder (GAD), in adults with genetically confirmed PMD.