DDX3X and fragile X-associated tremor/ataxia syndrome: One hypothesis to explain the roles of DDX3X in the stimulation (Linsalata et al., 2019) or inhibition (Cheng et al., 2019) of RAN translation in FXTAS or C9oRF72-ALS/FTD respectively would be to consider the secondary structures of the repeat RNAs, with the CGG-repeats adopting predominantly G-quadruplexes while sense GGGGCC-repeats form a mixture of G-quadruplexes and hairpins.