FMR1 and fragile X syndrome: Abnormal weight has been frequently reported in adults with FXS.17 Impaired hypothalamic functioning in individuals with FXS due to decreased levels or absence of fragile X mental retardation protein (FMRP) could be a potential cause of abnormal weight gain in these individuals.3 Additionally, increased appetite is a common side effect of the psychotropic medications that are frequently used in patients with FXS.34