Fragile X syndrome

What causes it?

In fragile X, one of the genes on the X chromosome is faulty. When normal, this gene makes a protein necessary for brain development, but when it's faulty little or none of the protein is made.

The gene that causes fragile X is called the FMR1 gene. Pictures of the X chromosome show a constriction near the tip of the chromosome, so it looks as though the end of the chromosome is breaking off. The faulty gene causes this disruption in the chromosome.

Boys are usually more severely affected as they have only one X chromosome (they carry one X and one Y chromosome). Girls have a second X chromosome, which can to some extent make up for problems with the faulty one and so they may have only mild disabilities. They may also be carriers of the condition – that is, they are not affected themselves but can pass the condition on to their children.

However the genetics of fragile X are actually more complicated as some people only have a small change called a premutation in the FMR1 gene. While they don’t usually have problems from this , it makes the gene unstable and can develop into a full mutation when passed on to the next generation.

What are the symptoms?

The main problem in fragile X is intellectual impairment. This can range from very minor, so that the person has a normal IQ and shows no sign of fragile X, to severe learning difficulties. How badly someone is affected depends on the degree of change in the gene.

There are also often emotional and behavioural problems. These may include hyperactivity, impulsivity, attention deficit disorder, anxiety and mood swings.

There may also be characteristic physical features in fragile X including facial features, such as a long face and large ears, flat feet and hyperextensible joints.

Who's affected?

Fragile X affects about one in 3,600 men and one in 4,000 to 6,000 women of all races and ethnic groups. It shows an X-linked recessive pattern of inheritance and changes in the gene can become more serious as it's passed from parent to child (especially when it is passed from a woman who carries it to her child).

Some people with a permutation of FMR1 may have no, or minimal, fragile X symptoms. But those with full mutation, where larger changes in the gene exist, demonstrate more severe signs of the condition.

Despite being carriers, some men aren't affected (even though they have no normal copy of their X chromosome). But men who have the full mutation are almost always affected.

In women with the full mutation, a third have a below-normal IQ, a third have a borderline-normal IQ and the remaining third have a normal IQ.

How is it diagnosed?

Fragile X can be diagnosed using a DNA test on a sample of blood. Antenatal testing is possible using chorionic villus sampling or amniocentesis from about 11 weeks of pregnancy.

What's the treatment?

As yet there are no specific treatments or a cure for fragile X, but emotional and educational support for children and their families are vital to help them reach their best potential.

Most affected children have delayed speech and language development and specialised help from a speech and language therapist is vital. Behavioural therapy may help children and their families to cope with problems such as hyperactivity and impulsivity, and sometimes medication is tried. Behavioural therapy may also help those children who have problems developing relationships to develop social skills and to cope with stressful situations.

Some children cope in mainstream schools, sometimes with some extra help, while others need to go to a school which can provide for their special educational needs.

Advice and support

The Fragile X Society

• Tel: 01371 875100
• Website: www.fragilex.org.uk