Fragile X syndrome, the most common cause of inherited intellectual disability and autism spectrum disorders (ASDs), is associated with a variety of cognitive, developmental, and behavioral symptoms, as well as physical features.

Symptoms differ in severity and occurrence among patients. While the disease occurs in both sexes, males are more frequently and generally more severely affected than females. Life expectancy for fragile X patients is generally normal.

Developmental and cognitive problems

Fragile X is characterized by moderate to severe intellectual disability, with significant cognitive impairment present in most males and one-third of females. Problems in executive function, a set of mental skills that include working memory, flexible thinking, and self-control, are also common.

Affected children may develop speech and language skills later than other children their age, but most patients are verbal. Their ability to understand others may also be better than their ability to use words to express themselves.

Motor delays are often present, with difficulties in movement coordination and muscle strength. Problems in sensory processing are also common, with patients feeling overwhelmed by loud sounds, bright lights, movements, touch, and even by smells and tastes.

Physical features

Most boys and some girls with fragile X have characteristic physical features that may not be obvious until puberty.

Distinctive features can include a long and narrow face, prominent forehead and chin, large protruding ears, and crossed or poorly aligned eyes (strabismus). Patients may also show low muscle tone, flat feet, and overly flexible joints, especially those of the fingers, and soft and smooth skin. Boys often have large testicles after puberty.

Behavioral symptoms

People with fragile X commonly exhibit behavioral problems, such as hyperactivity, attention difficulties, impulsivity, obsessive-compulsive disorder, depression, anxiety, and mood instability. Also frequent are ASDs and autistic behaviors, including communication and social difficulties, poor eye contact, repetitive movements, and repetition of phrases and noises said by others.

Self-injuring and aggressive behaviors, like hand-biting and hitting, are also very common in fragile X, especially among males, as are psychiatric disorders such as attention deficit hyperactive disorder (ADHD), and obsessive-compulsive behaviors, depression, and anxiety. Psychosis can also be present, but is seen in less than 10% of all cases.

Other symptoms

Additional symptoms may include eye and vision problems, frequent ear and urinary infections, gastrointestinal disorders, heart valve defects, scoliosis or curvature of the spine, and groin hernias. Regular medical checkups and awareness of  health risks may improve the outlook for those affected.

People with fragile X are also at an increased risk of epilepsy, with 14% to 18% of males and about 6% of females experiencing seizures.


Last updated: April 14, 2021


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