CSTB and fragile X syndrome: In the past decade, however, there has been a growing exploration of tandem repeat GQs as their biological relevance to neurological disorders [14,15,16], such as fragile X syndrome (FXS), which is mainly caused by the GQ-forming trinucleotide repeat expansions in FMR1 [17,18], and progressive myoclonus epilepsy (EPM1), which is reported to be related to the GQ-forming dodecamer repeat expansions in CSTB [19,20], has been discovered.