A Brief Introduction to Fragile X Syndrome

According to the National Institute of Health, fragile X syndrome is a genetic condition that causes a range of developmental problems including learning disabilities and cognitive impairment.

Fragile X syndrome is a hereditary X-linked dominant pattern, which means the mutation is located on the X chromosome. Men have one X chromosome (and one Y chromosome) and women have two. Since this mutation is dominant, all it takes is a mutation on one of the three X chromosomes for a child to inherit fragile X syndrome.

Mutations (the changing of a structure in a gene) in the FMR1 gene cause fragile X syndrome. FMR1 provides the instructions for making the protein FMRP, which regulates the production of other proteins and helps develop the connections between nerve cells. These connections between nerve cells are essential to relaying nerve impulses throughout the body. Most cases of fragile X syndrome occur when a specific DNA segment is repeated much more than usual within the gene. Typically, this segment repeats itself 5-40 times; but it repeats itself more than 200 times in people with fragile X. The expanded segment turns off the FMR1 gene, thereby preventing the gene from producing the protein that helps develop the connection between nerve cells.
 
This disorder typically affects males more than it does females, occurring in approximately 1 in 4,000 males and 1 in 8,000 females. While most males with fragile X syndrome have intellectual disabilities, only one-third of females with the disorder are intellectually disabled. Parents can start seeing signs of fragile X syndrome in their child by the time he or she is two years old.

Some signs that a child may have fragile X syndrome are:

• Delayed development of speech & language
• Hyperactivity
• Having attention deficit disorder (ADD)
• Having features of autism spectrum disorders that affect communication and social interaction - this occurs in 1/3 of affected individuals
• Seizures - these occur in 5% of affected females and 15% of affected males

People with fragile X syndrome begin to develop more distinctive features as they age, including

• A long, narrow face
• Large ears
• Prominent jaw
• Prominent forehead 
• Unusually flexible fingers
• Flat feet 

Information obtained from: Genetics Home Reference