Fragile X Syndrome

Fragile X syndrome, also known as Martin-Bell syndrome or FXS, is the most common known cause of inherited intellectual disability, occurring in an estimated 1 in 4000 males and 1 in 6000 to 8000 females. A family of genetic syndromes that are caused by changes in the same gene, Fragile X can result in impairments in a spectrum that ranges from mild learning problems with a normal range IQ to severe developmental disabilities. Fragile X is also the most frequent known cause of autism spectrum disorders and autism-like behaviors.

Autism and Fragile X Syndrome

Fragile X Syndrome: Causes

FXS is caused by a mutation in a gene on the X chromosome that interferes with the production of a protein needed for proper brain development. This mutation causes the gene, called the FMR1 gene, to make very little of this protein or none at all, causing changes in every cell of an affected individual's body, which can lead to a number of physical characteristics common to individuals with FXS as well as cognitive issues, behavioral problems, and a number of developmental delays and impairments.

FXS is an inherited genetic disorder, the mutated X passed from one generation to another in affected families. The FMR1 gene can be passed from parent to child in a premutation form, which then may or may not fully mutate to cause Fragile X, or as a full mutation. Male children who inherit a fully mutated version of the FMR1 gene in the X chromosome will develop Fragile X, since males have just one X chromosome.

Female children, on the other hand, have two copies of the X chromosome, which often leaves them one normal X chromosome to fall back on to produce that essential protein, allowing proper development to occur. For this reason, girls are less likely to be affected by Fragile X than boys are, and those who do develop the syndrome are often more lightly affected than males with the disorder.

A father who carries the Fragile X mutation can only pass the milder, premutation form of the FMR1 gene to his daughters, even if he carries the full mutation gene. Fathers cannot transmit Fragile X to sons, since they contribute only Y chromosomes to male children.

Mothers who carry the altered gene can pass it to children of either sex, and can transmit the genetic condition in either the premutation or full mutation form. Mothers who have one mutated X chromosome and one normal copy have a 50 percent chance of passing the mutation to each child they bear, though they are very likely to show no symptoms of fragile X themselves.

In fact, an altered gene is often carried silently through many generations of a family without any members of that family showing symptoms. However, with each generation, the chances of having a child born with Fragile X syndrome from that altered gene increases.

Signs and Symptoms

This genetic disorder can manifest itself in a wide range of signs and symptoms that include physical, social, mental, and sensory characteristics. These vary from one affected individual to another, both in the particular combination of symptoms displayed and in their degree, even among those in the same family.

The most consistent effects of Fragile X are seen in cognitive or intellectual development. Approximately 80 percent of males with the disorder are affected by mental retardation, most in the mild to moderate range. Cognitive effects in females with Fragile X tend to be less severe, with only about one third having an IQ score that indicates mental retardation. Learning disabilities are common with Fragile X, as are attention disorders, anxiety, hyperactivity, and language processing issues.

Physical characteristics commonly associated with Fragile X can include an elongated face or jaw, prominent ears, a broad forehead, and a slightly larger than average head. Many individuals with Fragile X will be shorter than average, and loose, flexible joints are common. Males with Fragile X may develop enlarged testicles at the onset of puberty, and those with this syndrome can be prone to certain medical conditions, such as hernia, middle ear infections, and heart murmur, among others.

Fragile X and Autism

Individuals with Fragile X have a higher than average risk of developing autism spectrum disorders. In fact, Fragile X is the most common known single gene cause of ASD. About one third of children who are diagnosed with Fragile X also have autism, accounting for approximately 2-6 percent of overall autism cases diagnosed.

Many of the remaining two-thirds display behaviors and symptoms common to autism, but do not meet the criteria for an autism diagnosis. Among these are speech and language delays or abnormalities, communication and interaction difficulties, marked social anxiety, repetitive behaviors, sensory issues, and a strong preference for structure and routine.

Fragile X syndrome can be difficult to diagnose in children, especially those who are mildly affected. Parents of children who have been diagnosed with autism or who have noted autism type symptoms in their children may be wise to request further testing to rule out Fragile X, ensuring that medical issues common to the disorder are not left untreated.

• Preschool Activities for Autistic Children
• Possible Causes of Autism
• Tips for Raising Kids with Autism
• What Is Your Autism Empathy Rating?

• Lesson Plans for Autistic Children
• Adult Autism Symptoms
• Social Skills Activities for Kids with Autism
• Speech Therapy Ideas for Autistic Children
• Famous Autistic People

• Autism Disorder Characteristics
• Considered Mild Autism
• Classical Autism
• Main Page
• What Is Fragile X Syndrome