Fragile X syndrome (FXS) is the leading monogenic inherited form of intellectual disability (ID) and autism spectrum disorder (ASD) and is caused by a cysteine-guanine-guanine (CGG) trinucleotide repeat expansion in the fragile X messenger ribonucleoprotein 1 (FMR1) gene (> 200 repeats) located on the X chromosome [1, 2]. The gene discussed is FMR1; the disease is autism spectrum disorder.