Fragile X syndrome is the most common inherited form of mental retardation (1, 2). It affects about 1 in 4,000 males and 1 in 8,000 females and occurs in all racial and ethnic groups (1, 2). Fragile X syndrome is a genetic disorder that runs in families. It is caused by an abnormality in a single gene.

• Some degree of mental retardation or learning disabilities.
• Behavioral problems, such as difficulties paying attention and frequent tantrums.
• Autistic-like behaviors, such as hand flapping and hand biting.
• Delays in learning how to sit, walk and talk.
• Speech problems.
• Anxiety and mood problems.
• Sensitivity to light, sounds, touch and textures.
• Subtle physical features, sometimes including a long narrow face, large ears, a high arched palate, flat feet, and overly flexible joints (especially the fingers). Males tend to develop enlarged testicles after puberty.

Girls with fragile X syndrome generally have fewer physical signs of the disorder than males, though some have large ears. While most males with fragile X syndrome have mental retardation or serious learning disabilities, only about one-third to one-half of affected females do (2, 3). However, some affected girls with normal intelligence have learning disabilities involving math, attention difficulties, emotional problems (such as anxiety, depression and shyness), and poor social skills (4).

Most children with fragile X syndrome do not have serious medical problems and generally have a normal life span. However, about 20 percent develop seizures, which generally can be controlled with medications (5). Children with fragile X syndrome may be at increased risk for chronic inner ear infections (otitis media) and may require the surgical insertion of drainage tubes (tympanostomy).

Heart murmurs may occur more frequently and are often caused by a condition called mitral valve prolapse (4, 5). This condition usually is not life-threatening, but individuals with mitral valve prolapse generally need to take antibiotics before dental care.