C9orf72 and amyotrophic lateral sclerosis: The genetic defects that cause ALS are still being elucidated, although 50% of ALS cases result due to mutations in chromosome 9 open reading frame 72 (C9orf72), superoxide dismutase 1 (SOD1), transactive response DNA-binding protein (TARDBP) or fused in sarcoma (FUS) [126,127,128,129].