16 06 2018
Carrier screening for genetic diseases Preconception, Early pregnancy test Genesis Perinatal Care Clinic
Carrier screening in early pregnancy.Advances in genotyping technology resulted in the fast and affordable sequencing of the human genome (genetic information). Conditions like cystic fibrosis (1/25 risk of being a carrier) and spinal muscular atrophy (1/47 -1/90 risk of being a carrier) thalassemias (almost 7% of women are carriers ) are relatively common conditions with a significant impact on the life of the affected individual. Expanded carrier screening can identify not only common recessive conditions but also rare ones. This was till recently offered only as a preconception test. However as Carrier screening can now be completed at a very fast pace it is an option to be considered as an early pregnancy test.
What is carrier screening?
Carrier screening is a type of genetic test that can tell you whether you carry a gene for certain genetic disorders. When it is done before or during pregnancy, it allows you to find out the chances of having a child with a genetic disorder
For some genetic disorders in order for the child to be affected, it needs to inherit the abnormal gene from both parents (autosomal recessive). Individuals who have one abnormal gene are most of the time asymptomatic meaning they do not have the disease or have a very mild form. However, they can pass the abnormal gene to their children. these individuals are called Carriers. For example, for Cystic fibrosis, the carrier is usually completely symptomatic while for B thallasemia the carrier might have mild anemia.
Who should have carrier screening?
It is currently recommended for women to consider having screening for cystic fibrosis, hemoglobinopathies and spinal muscular atrophy if they are planning to get pregnant
How is the testing done?
Usually, a sample of blood is required although some test uses saliva for swab taken from the mouth. The test comes as positive (you have an abnormal variant) or negative (you don’t). If you are found to be a carrier then your partner should be tested to determine his status
Normally you do not need to repeat the test in the future for the same mutation
Should everyone have carrier screening?
Carrier screening in most settings is a voluntary decision. The same applies to the extent of screening you will have. Meaning whether you will opt for a targeted screening or expanded
What is expanded carrier screening?
Current tests offer the option to test for more than 200 conditions. They usually focus on conditions that although rare are expected to have a major impact on the person’s quality of life
How accurate are the tests?
The tests are not perfect. There is a small risk of both false positive and false negative results. A negative – normal test does not guarantee that there no chance for genetic disorders because; 1 does not test for everything 2. there may be a variant mutation that is not detected by the test but still cause problems
What the test providers are trying to calculate for you is the residual risk; meaning the risk after you have a negative test
the following table gives an example for cystic fibrosis
Gregg et al Expanded Carrier Screening Obstet Gynecol Clin N Am 45 (2018) 103–112
At Genesis Perinatal Care Clinic we are offering the most comprehensive carrier screening tests; The test can be scaled from the relatively common diseases to an expanded test that covers more than 270 serious diseases. We have built the proper setting to discuss, counsel and perform both screening and follow up diagnostic tests for genetic conditions
Dr George Michailidis, MRCOG
Fetal &Maternal Medicine Consultant
Obstetrician & Gynaecologist