Repeat expansion disorders (REDs) are a heterogeneous group of conditions that mainly affect the nervous system and include fragile X syndrome, the most common inherited form of amyotrophic lateral sclerosis and frontotemporal dementia (C9orf72-ALS/FTD)1 and inherited ataxias (Friedreich ataxia (FA), RFC1-CANVAS (cerebellar ataxia, neuropathy, vestibular areflexia syndrome)2). This evidence concerns the gene RFC1 and fragile X syndrome.