Abstract
A patient with delusion of pregnancy as an early feature of frontotemporal dementia with motor neurone disease (FTD/MND) who was reported some years ago was posthumously found to harbor the C9ORF72 hexanucleotide repeat expansion, now known to be the most common genetic cause of FTD/MND. Some series have found psychosis to be common in FTD associated with this mutation, so this test should be considered in individuals with clinical features of FTD and MND and/or with a family history of either disorder who present with bizarre delusions.