What is autosomal recessive inheritance ?

CEN4GEN inheritance patterns

Carrier screening was developed to help people learn about their risks of having children with certain genetic conditions. Most carrier screens focus on conditions that are inherited in an autosomal recessive fashion.

How do autosomal recessive conditions work ?
The rod-like structures in our cells that contain our genes and DNA are called chromosomes. Each cell has 23 pairs for a total of 46 chromosomes that contain thousands of genes that are also in pairs. One chromosome from each pair (and therefore all of the genes that are on that chromosome) comes from the mother, while the other chromosome comes from the father. In turn, each person passes on one copy of each of his/her pairs of chromosomes to his/her children, and so on. The first 22 chromosome pairs are the same in females and males, and they are called the autosomes.

CEN4GEN autosomal recessive inheritance

In autosomal recessive conditions, both copies of the gene pair need to be changed to cause a disease. If both copies are working, that person would not have that condition and would not be at higher risk for his/her children to be affected. However, if one of the gene copies is working, but the other is altered, that person is called a carrier. Carriers do not usually show any symptoms of the condition since their working copy is enough to make up for the non-working copy, but they are at risk for passing on the non-working copy to their children. If two carriers of the same condition have a child and each passes on their non-working copy, the child will have no working copies, and will be affected with the condition.

What does a negative result mean ?
Because no genetic test can look at every possible DNA change in a gene, the risk for being a carrier is never zero, but a negative test will significantly reduce your chance of being a carrier. CEN4GEN should be able to tell you how much lower your risk is with the negative result.

In most cases, there is no need to repeat this test in the future as our DNA does not change over time. However, not all carrier screens are the same. The number of conditions and the types of DNA changes included on each screen will differ between laboratories and even over time as more is learned about genetics. If your partner is a carrier of a genetic condition or if your medical history or that of your family members’ changes, you will want to discuss this with your healthcare provider in order to make sure you have had the most appropriate carrier screen to assess your risks given this new information.

What does a positive result mean ?
If you test positive for being a carrier of an autosomal recessive condition, this does not mean that you are at risk for developing symptoms of the condition. You are, however, at an increased risk for having a child with that condition.

What about my partner ?
For most people who test positive for being a carrier, the next step is discussing carrier screening with your partner. Remember, both parents have to be carriers to be at higher risk of having an affected child. Your partner can have the same carrier screening as you, or a more detailed test called gene sequencing. The advantage to gene sequencing is that it will look for even more changes in the gene often missed by routine carrier screening, but can also cost more or take longer for results. Your partner may have already had carrier screening, so it is important to ask. Because no genetic test can look at every possible DNA change in a gene, the risk for being a carrier is never zero, even after testing negative on a carrier screen. Knowing what conditions were included in the carrier screening and the specific DNA changes analyzed by the screen will help determine the final chance of passing a genetic condition onto your children.

What else should I consider ?
If both you and your partner are carriers of changes in the same gene, there is a 25% (1 in 4) chance with each pregnancy that the child will inherit a non-working gene copy from each of you and have the condition. If you are currently pregnant, there are tests available (called chorionic villus sampling and amniocentesis) to see if the child you are carrying is affected.

You may also wish to discuss these results with other family members, as they are now at increased risk for being a carrier as well. It is helpful to share a copy of your test results with your family members so they can bring them to their own healthcare provider to determine if carrier testing is right for them. Regardless of your partner’s carrier status, each of your children will have a 50% (1 in 2) chance of being a carrier, and your results should be shared with them in the future so they can have appropriate testing if they desire it.