FMR1 and fragile X syndrome: Nonetheless, two cases were identified, where expression of a full-mutation gene caused severe FXTAS (Loesch et al., 2012; Santa Maria et al., 2014), thus supporting the idea that a fully mutated FMR1 transcript can have toxic effects and that elongated transcripts are causative for FXTAS, but not for FXS, although some mRNA is present in many FXS patients (Tassone et al., 2001).