Fragile X syndrome

Fragile X syndrome is the most common inherited form of intellectual disability. It affects about 1 in 4,000 males and 1 in 6,000 to 8,000 females and occurs in all racial and ethnic groups.

Fragile X syndrome is caused by an abnormality in the FMR-1 gene located on the X chromosome.  Each person has 23 pairs of chromosomes, or 46 individual chromosomes. The pair of sex chromosomes (X and Y) determines whether a person is male or female. Females have two X chromosomes, and males have one X chromosome and one Y chromosome. Because females have two X chromosomes, a female who inherits one X chromosome with the abnormal FMR-1 gene still has the other unaffected X chromosome. Therefore, girls are affected by fragile X syndrome less frequently than boys and their symptoms are usually not as severe. Boys are usually more severely affected because they have only one X chromosome, and it contains the abnormal gene.

Fragile X is inherited and passed on through the mother’s side of the family.  Any woman who has a brother or male relative with fragile X syndrome may want to meet with a genetic counselor.  A genetic counselor can help her to better understand the complicated genetics and inheritance of fragile X syndrome.

Children and adults with fragile X syndrome may exhibit a number of signs.  These can range from mild to severe. Some common symptoms include:

• Some degree of intellectual disability or learning problems
• Behavioral problems, such as difficulty 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

Most boys with fragile X syndrome have intellectual disabilities, but only about one-third to one-half of affected girls do. However, affected girls with normal intelligence may have some of the following symptoms:

• Learning disabilities involving math
• Attention difficulties
• Speech delays
• Emotional problems, such as anxiety, depression and shyness
• Poor social skills

While most children with fragile X do not have any medical conditions, about 15% of boys and 5% of girls develop seizures.  These can usually be controlled with medication.  Children with fragile X may also be at increased risk for multiple ear infections and they may need to have tubes placed in their ears.  Older children and adults may have heart murmurs, but usually no treatment is necessary.

There is no cure for fragile X syndrome. But, an individualized treatment plan, beginning as soon as possible, can help children reach their full potential. Most children with fragile X syndrome can benefit from treatment by a team of health professionals and special educators. The team may include speech/language therapists, physical and occupational therapists, special educators, psychologists and pediatricians.

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