However, several genetic studies reported other PFN1 mutations (A20T, T109M, R136W and Q139L) identified in FALS (0.5–2%) or SALS (0.2–0.8%), confirming that, although rare, PFN1 mutations can cause ALS [5,6,7,8], sometimes presenting as an atypical flail leg syndrome [8]. This evidence concerns the gene PFN1 and amyotrophic lateral sclerosis.