Fragile X is the most common inherited cause of mental impairment and the most common known cause of Autism. As yet, there is no known cure, but research is currently being carried out to learn more.

A change or mutation in a gene on the X chromosome causes the fragile X syndrome. Chromosomes are packages of genes that are passed from generation to generation. Most individuals have 46 chromosomes, two of which are sex chromosomes. In females, these are two X's; in males they are X and Y. Genes are given names to identify them and gene responsible for fragile X syndrome is called the FMR1 (fragile X mental retardation 1) gene. The mutation is in the DNA of the X chromosome. The gene appears in forms that are defined by the number of repeats of a pattern of DNA called CGG repeats. Individuals with less than 60 CGG repeats have a normal gene.

Individuals with 60-200 CGG repeats have a premutation, which means they carry an unstable mutation which can expand in generations. Individuals with over 200 repeats have a full mutation which causes fragile x syndrome. The full mutation causes the gene to shut down or methylate a region of the FMR-1 gene. Normally, the FMR-1 gene produces an important protein called FMRP. When the gene is turned off, the individual does not make fragile X mental retardatic protein (FMRP). The lack of this specific protein causes fragile X syndrome.

What are the common symptoms of Fragile X?

Features usually include:

• mental impairment, ranging from learning disabilities to mental retardation
• long face, large ears, flat feet
• hyperextensible joints, especially fingers
• ear infections
• squints (strabismus)
• seizures (epilepsy) affect about 25% of people with fragile x

Boys are typically more severely affected than girls. While most boys have mental retardation, only one-third to one-half of girls have significant intellectual impairment; the rest have either normal IQ and learning disabilities. Emotional and behavioural problems are common with both sexes.

About 20% of boys with fragile X meet full criteria for autism. Most boys and some girls have symptoms of autism, but tend to be very social and interested in other people.

Behavioural Characteristics include:

• attention deficit and hyperactivity
• anxiety and unstable mood
• autistic like behaviour
• repetitive speech
• lack of concentration
• delayed speech
• poor social skills

Fragile X Syndrome can also affect some carriers. Women carriers can suffer from premature ovarian failure (POF) and males over the age of 50 can suffer from Tremor/Ataxia Syndrome (FXTAS) which is a progressive neurological condition affecting balance and causing tremors and dementia. People suffering from fragile X are expected to have a normal life expectancy.

There is testing and genetic counselling available to those at risk. Testing should be done for any male or female with intellectual disability, significant developmental delay or learning difficulties, individuals diagnosed with Autism, or any individuals with a family history of Fragile X or any undiagnosed intellectual disability.

For further information about Fragile X  please visit the links page or contact us on

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