About Carrier Screening

Carrier screening is a genetic test used to determine if a person is a carrier of a recessive genetic disease, and provides information about reproductive risks prior to or during a pregnancy. Though most babies are born healthy, there is a small chance of having a baby with a severe genetic disease with every pregnancy. Carrier screening can help to inform about the health of your future children by predicting your chances of having a child with a genetic disorder.

Carriers and Diseases

What is a carrier?

All genes come in pairs, and we inherit two copies of each gene from our parents – one each from our mother and father. A carrier is a person who has a mutation (or change) in one copy which causes the gene to not work properly while the other works normally. The normal copy compensates for the abnormal one, so the carrier is typically healthy and shows no symptoms and is not at risk of developing a disease. This means people can be carriers of a disease-causing mutation without knowing it.

However, being a carrier means there is a risk of passing on the abnormal copy of a gene unknowingly to your child, and your child could be born with a genetic disorder.

Could I be a carrier?

Anyone can be a carrier, even if there is no family history of any genetic disorder. Because most carriers are symptom-free, most do not know that they are carriers until they have a child born with a genetic disorder, or until they have a carrier screening done.

What is an Autosomal Recessive Disorder?

Many conditions are caused by mutations, or changes, in the DNA. Autosomal recessive disorders are genetic disorders which are caused when a mutation is present on both genes of a pair. When both mother and father have this gene mutation and pass this on to their child, the child will have an autosomal recessive disorder. If both parents are carriers for the same genetic disease, there is a 1 in 4 chance, or 25 percent chance of having an affected child with each pregnancy. Parents can sometimes misunderstand the 1 in 4 risk. Parents who have one child affected by an autosomal recessive disorder may think that a 1 in 4 risk means that the next 3 children cannot be affected. This is not true. The risk is the same for every pregnancy .

How is the defected gene passed on by parents who are carriers?

There are three possible outcomes in pregnancy when both parents are carriers:

  • There is a 1 in 4 (25%) chance that the child will be born with an autosomal recessive disorder. The child will have inherited two changed genes, one from each parent.
  • There is a 2 in 4 (50%) chance that the child will be a carrier like the parents, but will not have any symptoms. The child will have inherited one normal gene and one abnormal gene (mutation).
  • There is a 1 in 4 (25%) chance that the child will not inherit the defected gene with a change (mutation) from either parent. This child will not be a carrier and will not be affected by the disorder.

Screening

What carrier screening should I have?

Asia Genomics offers a very comprehensive carrier screen which can detect over 100 health conditions – the Family Prep Screen. The conditions screened for include ones that can be treated early in life, ones that result in intellectual disabilities, some that are chronic and require lifelong management, and some that have no treatments available.

Learn more about the Family Prep Screen HERE.

Who should get screened?

Physician societies such as the American Congress of Obstetricians and Gynecologists ((ACOG), and the American College of Medical Genetics and Genomics (ACMG), recommend that pregnant women or anyone planning a pregnancy undergo carrier screening. The carrier screening provided through Asia Genomics is a single universal test that offers comprehensive analysis for all individuals independent of ethnic background.

Why should I get screened?

Carrier screening allows future parents to find out if they are carriers for a genetic disorder. With this information, you can make informed decisions, and choices that are consistent with your values. Carrier screening can also help to discover potential problems and allow you to seek early treatment. For example, Family Prep Screen covers many disorders that can be medically addressed if detected early. 59 of the diseases on the Family Prep Screen panel have treatments available.

We recommend that you discuss carrier screening and its benefits and limitations with a qualified health care professional, such as a physician or a genetic counsellor. This may help you decide if career screening is right for you.

Does my ethnicity affect carrier screening?

Some genetic disorders are more common among certain ethnic groups, so your ethnic background and family history does affect the chances of you being a carrier. For example, the carrier frequency of Alpha- and Beta Thalassemia is higher in Asian, African American, Hispanic, Mediterranean and Middle Easter populations as compared to other populations.

Other genetic disorders are relatively common regardless of these factors and carrier screening is recommended regardless of ethnic background. These include Cystic Fibrosis, Spinal Muscular Atrophy, and Fragile X Syndrome.

When should I get screened?

Carrier screening can be done before, during and after pregnancy. However, a carrier screening test that is done at preconception (before pregnancy) will give you a broader range of options and more time to make an informed decision.

Do I need to have carrier testing for every pregnancy?

Carrier testing only has to be done once in your lifetime. If you are not a carrier, you remain at very low risk of having a child with the condition. However if you are a carrier and have a new partner, your new partner should be tested.

Results

How will I interpret my test results?

Proper counseling, both before and after the carrier screening test, is essential to help you understand the results of the test as there can be great emotional risk when a person finds out they are carriers of a specific genetic disorder. Your practitioner or genetic counselor will go over the test results, and you can ask them any questions you may have.

What if I find out I’m a carrier?

It is important to know that you have options. When two parents are carriers of the same genetic disease, their children have a one in four chance (25 percent) chance of having that disease. For certain diseases, such as the Fragile X syndrome, only the mother needs to be a carrier for the child to have a high risk. Knowing your carrier status before or early in your pregnancy gives you time to learn about your disorder and prepare.

What happens if my partner and I are both carriers of the same disorder?

There are alternative reproductive options that you and your partner can consider. Some options your physician may recommend are:

Preparation
Prepare for the possibility of raising a child with special needs. For certain conditions, treatment in the newborn period can improve outcomes. Finding out early helps to ensure that doctors are involved during delivery, and that treatment begins early. Preparation can include researching medical centers, informing family and friends, and securing the emotional and financial support you may need before the birth of your child.
Fertility treatments
Preimplantation genetic diagnosis (PGD) is a highly specialized procedure that enables a healthy pregnancy, even when two parents are known carriers. PGD is done along with in-vitro fertilization, as fertility treatments allow doctors to screen embryos for a specific disease before conceiving.
Prenatal diagnosis
Prenatal tests can be done during pregnancy to determine whether the condition in question was transmitted to the baby. Medical diagnostic procedures, like chorionic villus sampling (CVS) in the first trimester, or amniocentesis in the second trimester, can accurately predict the health status of the pregnancy.
Change of plans
Consider alternative methods of starting a family, such as adoption, egg or sperm donation, or even choosing not to have children.

Limitations

No genetic screen is able to identify every carrier for every disease. And while it covers many diseases and conditions, it cannot screen for all possible birth defects or genetic diseases.

If you would like more information or advice on any of our tests and services, please contact us at +65 6336 2050 or info@asia-genomics.com.