Neuropsychiatric features of C9orf72-associated behavioral variant frontotemporal dementia and frontotemporal dementia with motor neuron disease

Earlier reports of chromosome 9p-linked frontotemporal dementia (FTD) with amyotrophic lateral sclerosis (ALS) kindreds observed psychosis as a prominent feature in some patients. Since the discovery of chromosome 9 open reading frame 72 (C9orf72) hexanucleotide expansions as a cause of FTD and ALS, research groups and consortia around the world have reported their respective observations of the clinical features associated with this mutation. We reviewed the recent literature on C9orf72-associated FTD and ALS with focus on the neuropsychiatric features associated with this mutation, as well as the experience at University of California, San Francisco. The results and methodologies varied greatly across studies, making comparison of results challenging. Four reports found that psychotic features (particularly delusions) were frequent among mutation carriers, particularly when present early during the disease course, suggesting that this symptom category may be a marker for the mutation. Disinhibition and apathy were the most commonly reported early behavioral symptoms, but these may not be helpful in distinguishing carriers and noncarriers because of the symptoms' frequency in sporadic behavioral variant FTD. Other neuropsychiatric features were reported in different frequencies across studies, suggesting either a similar behavioral phenotype in carriers and noncarriers or reflecting the heterogeneity in clinical presentation of behavioral variant FTD due to C9orf72 expansions. Further studies with larger cohorts will be necessary to determine the neuropsychiatric presentation associated with this mutation.