Fragile X syndrome

Fragile X syndrome (FXS) is a genetic disorder.

History

FXS is caused by changes in a gene that scientists called the fragile X mental retardation 1 (FMR1) gene when it was first discovered.

Fragile x syndrome

• The FMR1 gene usually makes a protein called fragile X mental retardation protein (FMRP).
• FMRP is needed for normal brain development. People who have FXS do not make this protein.
• People who have other fragile X-associated disorders have changes in their FMR1 gene but usually make some of the protein.
• Females often have milder symptoms than males.
• It affects 1 in 7,000 males about 1 in 11,000 females have been diagnosed with FXS.

Signs and Symptoms

Signs that a child might have FXS include:

Boy with Fragile X syndrome playing with toy

• Developmental delays (not sitting, walking, or talking at the same time as other children the same age);
• Learning disabilities (trouble learning new skills); and
• Social and behavior problems (such as not making eye contact, anxiety, trouble paying attention, hand flapping, acting and speaking without thinking, and being very active).
• Males who have FXS usually have some degree of intellectual disability that can range from mild to severe.
• Females with FXS can have normal intelligence or some degree of intellectual disability.
• Autism spectrum disorder (ASD) also occur more frequently in people with FXS.

Inheritance

There is a place in the FMR1 gene where the DNA pattern CGG is repeated over and over again. In most people, the number of repeats is small (5 to 44 repeats), which is normal.

FragileX Silencing of the FMR1 Gene in Fragile X Mental Retardation Syndrome

Having more repeats can change how much protein is made, and it increases the risk for associated disorders and related concerns.   If the number of repeats is too large (more than 200 repeats), the gene turns off.  When the gene is turned off, no protein is made. Without the protein, the person develops FXS. This is called a “trinucleotide repeat disorder.” People get (inherit) the disorder from their parents.

Normal: 5 to 44 Repeats

Most people have about 5 to 44 repeats of the letters CGG in their FMR1 genes. This is considered a normal number of repeats. People with a normal number of repeats do not have FXS and are not at risk for having children with FXS.

Intermediate: 45 to 54 Repeats

People who have an intermediate number of repeats (about 45 to 54) do not have FXS. However, they may have a slightly higher chance of having some symptoms.

Premutation: 55 to 200 Repeats

People who have a premutation (about 55 to 200 repeats) do not have FXS. However, they might have another fragile X-associated disorder and related concerns. In addition, people with a premutation can have children with a premutation or full mutation (FXS).

With each pregnancy, women have a 50% chance of passing the premutation or full mutation on to their child (daughters or sons). The more CGG repeats the mother has, the more likely her child will have full mutation fragile X.

Men will have daughters with a premutation, but sons will not be affected.

Full Mutation (FXS): More than 200 Repeats

People with a full mutation (more than 200 repeats) have FXS. With each pregnancy, women have a 50% chance of passing fragile X on to their child (sons or daughters).

Testing/Diagnosis

• FXS can be diagnosed by testing a person’s DNA from a blood test.
• Testing also can be done to find changes in the FMR1 gene that can lead to fragile X-associated disorders.
• A diagnosis of FXS can be helpful to the family because it can provide a reason for a child’s intellectual disabilities and behavior problems. This allows the family and other caregivers to learn more about the disorder and manage care so that the child can reach his or her full potential.
• Anyone who is thinking about FXS testing should consider having genetic counseling prior to getting tested.

PDB 2cpq

Treatments

There is no cure for FXS. However, treatment services can help people learn important skills. To develop the best treatment plan, people with FXS, parents, and health care providers should work closely with one another, and with everyone involved in treatment and support—which may include teachers, childcare providers, coaches, therapists, and other family members. Taking advantage of all the resources available will help guide success.

Early Intervention Services

Early intervention services help children from birth to 3 years old (36 months) learn important skills. These services may improve a child’s development.

Fragile X syndrome Resources
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