C9orf72 and amyotrophic lateral sclerosis: The hexanucleotide GGGGCC repeat expansion in C9orf72 (chromosome 9 open reading frame 72, 9p21.2) is most commonly associated with amyotrophic lateral sclerosis and frontotemporal dementia [133–135], but has also been detected in rare cases of PD, Alzheimer’s Disease, psychosis and atypical parkinsonism [136–143].