FMR1 and fragile X syndrome: A G4-forming (CGG)n repeat expansion within mutant forms of the FMR1 gene locus induces aberrant expression of the G4 binding protein FMRP which leads to the neurodevelopmental Fragile-X syndrome (FXS), or the repeat-length-dependent neurodegenerative Fragile-X tremor and ataxia syndrome (FXTAS) (28,29).