Plasma GFAP levels significantly differed among ALS-FTD, pure FTD, and pure motor ALS patients (namely without clinical signs of FTD) with a negative A status (p = 0.001), with the post-hoc analysis revealing significantly higher levels in pure FTD (199.0 (132.3–293.9)) than in pure motor ALS subjects (n = 125) (152.2 (111.3–197.3), p = 0.001). The gene discussed is GFAP; the disease is frontotemporal dementia.