C9orf72 and amyotrophic lateral sclerosis: The pathological mechanism involvingC9ORF72 gene or its function are not clear, even if several studies showed a decrease in the mRNA levels of some C9ORF72 variants in ALS, which suggests a loss-of-function mechanism (DeJesus-Hernandez et al., 2011; Renton et al., 2011; Gijselinck et al., 2012; Mori et al., 2013b).