C9orf72 and frontotemporal dementia: TG species, such as TG(18:1_18:2_20:4), were elevated in FTD‐GRN subjects, and TG(16:0_12:0_20:4) in FTD‐C9orf72 patients, whereas TG(16:0_18:1_20:3) was decreased in MAPT (Figure 4A–C).