Accurate DNA testing for Fragile X is now available. The test is called ‘DNA Studies for Fragile X syndrome’. Any medical practitioner can now refer a patient to a geneticist or a developmental paediatrician to arrange the test. Cytogenetic studies (chromosome tests)should be carried out at the same time to eliminate the possibility of other genetic disorders.

Who Should be tested?

• It should be carried out on any male or female who has an intellectual disability of unknown cause, or is developmentally delayed along with other characteristics of Fragile X syndrome.
• It should also be carried out when a person shows autistic-type behaviour which is associated with learning problems. People who show any of the characteristic symptoms of Fragile X syndrome should be tested, whatever their family history, as should any person who has a family member diagnosed with Fragile X.
• If there is a history of intellectual disability in a family, individuals who show no symptoms of Fragile X should be tested to find out whether or not they are carriers. This is important for those who are thinking about becoming parents. Knowing their carrier status can help a couple to make decisions about family planning.
• Women who experience premature menopause (before the age of 40) or who have a family history of premature menopause should also be tested for Fragile X.

Tests for Fragile X carried out before 1991 may not be correct and the results of cytogenetic tests since then may be inaccurate. People who were tested before 1991 or who have only had a cytogenetic test should have a DNA test.

Prenatal Testing

Accurate prenatal testing is available for female carriers of the disorder. Two pre-natal tests detect the presence of Fragile X in the foetus.

• Chorionic villus sampling (CVS) is used when the foetus is between 10 and 12 weeks. A small amount of placenta is taken from the uterus for testing. Results are usually available within two weeks. In the second method, amniocentesis, a small amount of amniotic fluid which contains foetal cells is removed. The test is usually done between the 14th and the 18th week of pregnancy. Growing and testing of the cells can take two to four weeks. Using this test, a woman wishing to find out if her baby is free from Fragile X might have to wait until she is 22 weeks pregnant for a result.
• A new test has recently become available, called preimplantation genetic diagnosis (PGD). This involves taking a single cell from an embryo before it implants in the uterus. The cell can be tested to see if the Fragile X chromosome has been inherited. An IVF cycle is needed to produce the embryos for testing. There are only a few specialized centres in the world performing PGD. This test is available in Australia. Current official indications for testing for Fragile X syndrome are available on the website of the Human Genetics Society of Australasia, under ‘Policies’. The first three of these indications are covered by Medicare.