C9orf72 and frontotemporal dementia: To determine the histopathological basis of the incidence of PD observed in families with a history of ALS/FTD with C9ORF72 expansion, Johnathan et al. extracted DNA from 377 brains with a histopathological diagnosis of idiopathic PD (iPD) or related diseases, and analyzed the amplification of C9ORF72.