C9orf72 and frontotemporal dementia: Remarkably this is associated with overall reduction of phenylalanine (Phe) abundance in the total proteome of antisense repeat overexpressing cells and decreased expression of proteins with high Phe content in FARSA knockdown cells, C9orf72 patient-derived cell lines, and post-mortem cerebellum tissue from C9orf72 ALS and FTD patients.