GJC2 and fragile X-associated tremor/ataxia syndrome: These include studies that implicated SCN2A in EA9 (OMIM # 618924; Liao et al., 2010), GJC2 in SPG44 (OMIM# 613206; Orthmann-Murphy et al., 2009), PGN in the autosomal dominant SPG7 (Sánchez-Ferrero et al., 2013), FMR1 in fragile X tremor/ataxia syndrome (FXTAS, OMIM # 300623; Hagerman et al., 2001), and DARS2 in hereditary SPG (Lan et al., 2017).