C9orf72 and mild neurocognitive disorder: The major genetic cause of familial frontotemporal lobar degeneration (FTLD), and of familial motor neurone disease (MND), is associated with the possession of a hexanucleotide expansion in C9orf72 gene, this occurring in about 20% cases of familial FTLD and 80% cases of familial MND 1, 2.