The short tandem repeat (STR) expansions of DNA were discovered to cause hereditary diseases in the early 1990s and are currently known to be linked with more than 50 developmental, neurodegenerative, or neuromuscular diseases [1], including fragile X syndrome (FXS), several spinocerebellar ataxias (SCAs, including the most recently reported SCA50/ATX-FGF14 [2,3]), Huntington’s disease (HD), myotonic dystrophies types 1 and 2 (DM1 and DM2), and frontotemporal dementia/amyotrophic lateral sclerosis (FTD/ALS). This evidence concerns the gene FGF14 and fragile X syndrome.