What Is Fragile X Syndrome?


Fragile X syndrome, along with cystic fibrosis and spinal muscular atrophy, is one of the three conditions for which expectant parents should receive carrier testing. However, it is one of the lesser-known and rarer genetic conditions. If you’re expecting a baby you believe may be at risk of Fragile X syndrome, it is important to opt for pre-pregnancy genetic testing as soon as possible. Here’s what you need to know about Fragile X syndrome.

What Is Fragile X Syndrome?

Fragile X syndrome (FXS) is a genetic disorder that children inherit from their parents. The condition leads to intellectual and developmental disabilities. Boys suffer from FXS at higher rates than girls and with more severe symptoms – every 1 in 4,000 boys will have FXS, while 1 in every 8,000 girls will have FXS.

This condition is chronic and impacts a person in all areas of their life. Over time, children with FXS can develop health conditions such as seizures, hearing and vision problems, and heart conditions. Only a few people with FXS develop the skills to live independently without a caregiver or parent.

Symptoms of Fragile X Syndrome

FXS leads to several symptoms, both developmental and physical. Boys tend to have more severe symptoms than girls. Children with FXS will display the following common symptoms:

  • Poor impulse control and temper tantrums
  • Anxiety
  • Hyperactivity and trouble concentrating
  • Issues with language or speech
  • Issues with developing certain skills, such as walking, crawling, or sitting
  • Sensitivity to light and sound
  • Hand-flapping and an aversion to eye contact

Some children with FXS will also experience physical changes to their face and body. Not all FXS children will have these characteristics, however. These physical symptoms can include:

  • Flat feet
  • A large head, forehead, and chin
  • Loose joints
  • Large ears
  • A long, narrow face
  • Trouble getting pregnant
  • Early menopause
  • Enlarged testicles after puberty

Causes of Fragile X Syndrome

Parents who carry the FXS genes pass the condition on to their children. Scientists link the development of FXS to the FMR1 gene, which produces a protein known as FMR that allows nerve cells to communicate with one another. This protein is necessary for normal brain development. Children who have FXS make either too much FMR or too little.

The FMR1 gene is on the X chromosome, which both parents can pass on to their children. In genetics, women have a XX chromosome sequence and men have an XY chromosome sequence. When two people have a baby, the mother provides an X chromosome and the father can provide either an X or Y chromosome, which determines the baby’s gender. As such, mothers with the FMR1 gene abnormality have a 50% chance of passing on FXS to their children. Fathers can only pass the FMR1 gene abnormality to their daughters.

Boys are more likely to have FXS than girls with more severe symptoms, because boys only have one X chromosome. Girls have two X chromosomes, so they have a higher chance of producing normal FMR proteins or stabilizing their FMR levels.

The Importance of Genetic Testing

If you believe that you could pass Fragile X syndrome to your child, it is important to receive carrier testing as soon as possible. This testing can help you identify if you or your partner carry the gene for certain conditions that you can pass on to your child. In addition, you can put your mind at ease and make informed family planning decisions. Before you conceive, opt for carrier testing to benefit your baby’s future.




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