Disease_Mapped_To_Gene Pediatric Endocrinology Terminology Cellosaurus Disease Terminology Repeat Expansion Disease Syndrome Rare Non-Neoplastic Disorder FMR1 Gene Fragile X Syndrome Cellosaurus Disease or Syndrome An X-linked dominant syndrome caused by expansion of the CGG triplets in the 5' promoter region of the FMR1 gene to over 200 copies. This expansion becomes hypermethylated, silencing the FMR1 gene expression, and subsequently completely inhibiting the expression of the fragile X mental retardation protein 1 (FMRP). The condition is characterized by a variety of developmental, emotional, behavioral, and physical symptoms, including learning disabilities and macroorchidism. Intermediate expansion of the CGG triplet (between 55 and 200 repeats) may be associated with a milder phenotype due to reduced expression of FMRP. NICHD A genetic syndrome caused by mutations in the FMR1 gene which is responsible for the expression of the fragile X mental retardation 1 protein. This protein participates in neural development. This syndrome is manifested with mental, emotional, behavioral, physical, and learning disabilities. Fragile X Syndrome Fragile X Syndrome C84717 C0016667 X-Linked Inherited Disorder NICHD Terminology