Links Between the C9orf72 Repeat Expansion and Psychiatric Symptoms.

PURPOSE OF REVIEW: To present recent findings on the links between the C9orf72 expansion and psychiatric impairment.

RECENT FINDINGS: Repeat hexanucleotide expansions in the C9orf72 gene are a cause of familial frontotemporal dementia (FTD), amyotrophic lateral sclerosis (ALS), and the mixed phenotype, FTD-ALS. Symptomatic expansion carriers display higher rates of psychotic and other psychiatric symptoms than non-carriers. Neuroanatomical associations of these symptoms have been found in cortical and subcortical areas. Family members of symptomatic carriers have higher rates of primary neuropsychiatric disorders than control populations, and the C9orf72 expansion may contribute to this association. However, the expansion does not appear to directly cause primary psychiatric disorders. While there is strong evidence associating the C9orf72 expansion with psychotic symptoms in carriers and psychiatric disorders in their kindreds, the link between these two phenomena, if any, remains unclear.