Other Names: FRAXA syndrome, Marker X syndrome, Martin-Bell syndrome


Fragile X syndrome is a genetic condition involving changes in the X chromosome. Fragile X causes a range of developmental problems such as learning disabilities and cognitive impairment. It is the most common form of inherited intellectual disability in males and a significant cause of intellectual disability in females. Some of the symptoms include:

  • Intellectual disabilities, ranging from mild to severe
  • Anxiety and unstable mood
  • Autistic behaviors, such as hand-flapping and not making eye contact
  • Sensory integration problems, such as hypersensitivity to loud noises or bright lights
  • Speech delay, with expressive language more severely affected than receptive language
  • Seizures (epilepsy) affect about 25% of people with Fragile X syndrome

Fragile X is characterized by developmental problems including intellectual disability and delayed speech and language development. Males are usually more severely affected than females. Additional features may include anxiety; attention deficit disorder (ADD); features of autism spectrum disorders that affect communication and social interaction; and seizures. Most males and some females with fragile X syndrome have characteristic physical features that become more apparent with age. Although some of the physical signs may be hard to recognize in babies and young children, they become more apparent with age:

  • Long face, large prominent ears, flat feet
  • Hyperextensible joints, especially fingers
  • Low muscle tone
  • Males may have large testes after puberty


Contact the Genetic and Rare Diseases (GARD) Information Center for more information on Fragile X Syndrome.