Family Prep Screen
Now available through Australian Clinical Labs
The Family Prep Screen, developed and validated by Counsyl, is a comprehensive carrier screening assay that assesses an individual's carrier status for more than 100 diseases by analysing up to 400 mutations. The Family Prep Screen tests for those conditions for which carrier screening is already quite common, such as cystic fibrosis, fragile X syndrome and spinal muscular atrophy. It's normal for someone to be a carrier. For the most part, this will have no impact on their own health. Most carriers have no known history of the disease in their family. What couples might want to know is whether they are both carriers for the same condition, placing them at increased risk of having children affected with the particular condition.
CARRIER COUPLES OF THE SAME RECESSIVE CONDITION HAVE A 1 IN 4 (25%) CHANCE THAT EACH OF THEIR CHILDREN WILL HAVE THAT GENETIC CONDITION.
Figure 1. Each parent passes on one copy of the gene to each of their children. Whether a normal copy of the gene (represented by the “R”), or a changed copy of the gene (represented by the “r”), is passed on by a carrier parent is random in each pregnancy.
What is the family prep screen?
Think of it as an ultrasound for your DNA. The Family Prep Screen tests for over 400 gene changes associated with more than 100 different genetic disorders. Carrying a gene change may not affect you*, but can affect your children. If both you and your partner are carriers of the same genetic disorder, your child has a 1 in 4 chance of being affected*. The only way to know your carrier status is through testing.
*Note: Only females undergoing testing will be screened to see if they carry the common gene change known to put them at risk of having a child with fragile X syndrome (FXS). FXS is inherited in a different way to the other diseases screened for by this test and does not require the male partner to also be a carrier in order for the couple to be at risk of having a child affected with the condition. Unlike the other conditions screened for in this test, being a carrier for FXS can have implications for a women’s own health. Women found to be carriers for FXS have an increased risk of developing the following conditions themselves:
1) Premature menopause (before age 40): approximately 20% of female FXS carriers will experience premature menopause.
2) Fragile X – Associated Tremour Ataxia Syndrome (FXTAS): approximately 16% of female FXS carriers over age 50 will develop FXTAS which is a condition that results in worsening unsteadiness (ataxia) and tremour.
For women found to be carriers of FXS, the risk of having an affected child will depend on the size of the gene change found. *Note: Women can choose not to be screened for FXS carrier status if they would prefer not to have this included in their test. This is done by simply ticking the appropriate box on the test request form provided to you by your doctor.
What causes these genetic conditions?
With the exception of fragile X syndrome (see left), and X-linked juvenile retinoschisis, the conditions tested for are called recessive conditions. Everyone has two copies of most genes as we inherit one copy from each of our parents. Sometimes a change is present in one copy of the gene which prevents the gene from working normally. Having a change in one copy of the gene has no effect on your health as you still have another working copy of the gene. Such people are referred to as “carriers”. As shown in Figure 1, when both parents are carriers, every time they have a child there is a 1 in 4 (25%) chance that child will inherit two changed copies of the gene and be affected by that particular condition. It is important to know that if you already have children who do not have one of these conditions it does not mean that you are not a carrier and are not at risk of having a child with that condition.
What do the results of this test tell me?
There are two possible outcomes when being tested. Your results may indicate you are either:
• A Carrier: this means the test has identified that you carry a change in one copy of one or more of the genes tested for. Testing of your partner will determine your risk of having a child with that condition(s).
• A Non-Carrier: this means you were not found to carry any of the gene changes tested for. Importantly, the test cannot detect all possible changes in the tested genes and thus cannot completely exclude the possibility that you are a carrier. By excluding you as a carrier of the gene changes tested for, your risk of being a carrier, or of having a child with any of the conditions, is significantly reduced.