What Causes Fragile X Syndrome?

Reviewed on 11/21/2020

What causes fragile X syndrome?

Fragile X syndrome is a genetic condition that leads to developmental delays and other problems.
Fragile X syndrome is a genetic condition that leads to developmental delays and other problems.

Fragile X syndrome (FXS) is a genetic disorder. It is passed down from parents to their children. A genetic disorder means the genes of either parent are faulty.

A gene is the basic unit of transfer of characteristics from parents to children. Genes are present in the DNA inside the cells. A child gets one set of genes from each of their parents. The gene named FMR1 lies on the X chromosome. This gene makes a protein called FMR that helps nerve cells communicate with each other. A child needs this protein for normal brain development. In FXS, this protein is either absent, deficient or abnormal.

There is a 50 percent chance of passing these faulty FMR1 genes from women to their babies. A father can only pass it to their daughters.

Therefore, boys are more likely to have FXS than girls and they have more severe symptoms because girls have two copies of the X chromosome. Even if one X chromosome has the gene defect, the other copy of the X chromosome can be fine and show no effect in most girls. Boys have only one copy each of X and Y chromosomes. If there are changes in the X chromosome, they will have symptoms of FXS.

However, some people show no symptoms despite inheriting fragile X genes. They are called carriers. These carriers can pass the gene change to their children.

What is fragile X syndrome?

Fragile X syndrome (FXS) is a genetic (hereditary) condition, meaning it runs in families and parents can pass it down to their children or grandchildren. Kids with FXS exhibit developmental delays, delayed milestones, poor intellect and mental retardation. Some may have tremors in their extremities and problems with balance. They may also have mood disorders and problems with balance and walking. Both boys and girls can be born with FXS, but it is more common in boys.

What are the symptoms of fragile X syndrome?

It is very difficult to spot a kid with fragile X syndrome (FXS) when they’re very young. Some kids with FXS may behave very similar to those with autism spectrum disorder. They mostly show symptoms of attention-deficit hyperactivity disorder (ADHD) or are hyperactive or even just active and have trouble paying attention.

If your child has FXS, they may

  • Be either very social or withdraw from social interactions
  • Show aggressive and self-destructive behavior (in boys) such as biting things
  • Flap their hands unnecessarily
  • Avoid eye contact
  • Be shy
  • Have language problems or delayed rapid or repetitive speech
  • Have mild, undiagnosed or severe learning difficulties
  • Have poor fine and gross motor skills
  • Have trouble learning skills such as sitting, crawling or walking
  • Show temper tantrums
  • Have poor impulse control
  • Have anxiety
  • Show extreme sensitivity to light or sound

Younger children with FXS may not display any specific physical features of this syndrome. Many will begin to develop certain features at the onset of puberty that are typical of those with FXS. These features include a narrow face, a large head, large ears, flexible joints, flat feet and a prominent forehead. These physical signs become more obvious with age.

Often, it is milder in girls. While most boys with FXS have learning and developmental issues, girls usually do not have them.

Girls with FXS may sometimes have problems with getting pregnant when they grow up. They might also go into menopause earlier than usual.

This condition may cause health problems such as

How is a child diagnosed with fragile X syndrome?

  • Your doctor may ask about your family history regarding fragile X syndrome (FXS), autism, attention-deficit hyperactivity disorder (ADHD) or any learning difficulties and cognitive functional delays in the previous child.
  • Your doctor may suggest a DNA blood test to check for FXS in your child.

Can fragile X syndrome be cured?

Because it is a genetic disorder, there is no medicine to cure fragile X syndrome (FXS). However, there are some treatments to help your child learn more easily and manage their behavior problems.

  • Special education and learning plans that guide their schooling and provide support
  • Speech and language therapy
  • Occupational therapy to help children manage daily tasks more easily
  • Behavior therapy
  • Medicines to prevent seizures or to manage attention-deficit hyperactivity disorder (ADHD) symptoms such as hyperactivity and other behavioral problems

It is better if you start these treatments in the early stages of a child’s life. Work with your child’s doctor, teachers and therapists on a treatment program. Learn about FXS to support your child.

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References
Medscape Medical Reference

CDC


NIH Eunice Kennedy Shiver National Institute of Child Health and Human Development


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