C9orf72 and Parkinson disease: The GGGGCC hexanucleotide repeat expansion (HRE) in the C9orf72 gene is the most frequent genetic cause of frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS).1,2 Movement disorders (MD) are frequently observed in C9orf72 HRE carriers,3 generally alongside the features of FTD or ALS, with parkinsonism being present in up to 40%.4