Discovering and proving the modifiers of rare diseases is not an easy task but repeat interruptions have drawn much attention due to different effects on phenotype, which have been described in several repeat expansions diseases, e.g., fragile X syndrome (FXS), a few types of spinocerebellar ataxias (SCA1, SCA2, SCA10, SCA17), and DM2 [29,30,31,32,33,34]. The gene discussed is ATXN10; the disease is fragile X syndrome.