Family doctor

Overview:

• Fragile X syndrome is an inherited condition and is the most common inherited mental handicap
• It affects boys worse than girls and can cause significant learning difficulties
• Unaffected family members can pass the genetic disorder onto their own children or grandchildren
• The syndrome may not be recognised until mid-childhood
• Treatment involves behavioural therapy, special education, speech therapy, and medication in some cases
• New testing strategies are being recommended to identify carriers of the gene

What is it?

Fragile X syndrome is an inherited condition and is linked to a problem with the X chromosome.

Boys are generally more severely affected than girls, probably because girls carry two X chromosomes - one of which is presumed to be normal.

The disorder causes a mental disability in about one in 4000 boys and one in 8000 girls.

Most boys will need extra help at school and may never be able to live on their own. Girls may have milder learning problems and many grow up to live independently.

Half of girls with the gene are not considered mentally disabled, but most have some learning problems.

Unaffected family members can pass the genetic mutation onto their own children or grandchildren, and in some cases the disorder has been passed on in families for many generations. In other circumstances the syndrome can skip several generations before it shows up again.

An estimated one in 250 women carry the fragile X premutation.

What are the symptoms?

Sometimes the disorder can go unrecognised until mid-childhood. However, the syndrome can be diagnosed by neonatal screening.

Most boys will show some level of mental retardation with an IQ of 60 or 70 (normal or "average" IQ is 100). An estimated 80 percent of affected boys and 35 percent of girls with the syndrome will have some degree of intellectual handicap.

Learning difficulties include slow learning, delayed speech, attention deficit disorder, and hyperactivity. Affected individuals may also show some form of autism and/or aggression.

Fragile X syndrome also has some physical characteristics that affect some individuals. Adult males may have a long face, large ears and large testicles.

Affected girls may have a thin face, and prominent ears.

Sufferers of both sexes may also have double-jointed fingers, flat feet and a heart murmur.

What can be done to help?

There is no cure for fragile X syndrome, but special education is available to help affected children.

Various forms of therapy can help including speech and occupational therapy.

Educational programmes should be developed to meet the individual's strengths and weaknesses. The child's behavioural problems and physical needs must also be addressed.

Medication can also be used in some cases to control hyperactivity, aggression, and/or depression.

Future trends

There is concern that information about the syndrome is not being passed down to new generations due to the disorder sometimes skipping several generations.

A new screening system to test girls at college or during ante-natal testing, or testing boys at birth is now being advocated to identify carriers earlier and enable them to make informed family planning decisions.

An Australian programme offering genetic testing to families affected by the syndrome has resulted in a reduction in the fragile X syndrome from 2.5 to 1 in 10,000 in the past 10 years.

Getting help

It is possible to screen for the syndrome while pregnant with the use of amniocentesis or chorionic villus sampling (CVS) and decide whether to continue with the pregnancy.

All couples with a family history of the disorder should seek genetic counselling prior to having children, and undergo screening during pregnancy.