Sickle cell anemia is an inherited condition that follows an autosomal recessive inheritance pattern. Even if you don’t have sickle cell anemia, you could be a carrier of the gene for it.
Sickle cell anemia is a genetic condition that’s present from birth. Many genetic conditions are caused by altered, or mutated, genes from either one of or both of your parents.
People with sickle cell anemia have red blood cells that are crescent-shaped, like a sickle. This unusual shape is due to a mutation in the hemoglobin gene. Hemoglobin is the molecule in red blood cells that allows them to deliver oxygen to tissues throughout your body.
The sickle-shaped red blood cells can lead to a variety of complications. Due to their irregular shape, they can become stuck within blood vessels, leading to painful symptoms. Additionally, sickle cells die off faster than typical red blood cells, which can lead to anemia.
Some genetic conditions can be inherited even if only one parent carries the gene. This is true of sickle cell anemia.
You have two copies of each of your genes — one from your mother and one from your father. Each copy of a gene is referred to as an allele.
Geneticists use the terms “dominant” and “recessive” to describe how a particular allele is expressed. If an allele is dominant, then you only need one copy for it to have its effect. If an allele is recessive, you’ll need two.
The sickle cell anemia trait is found on a recessive allele of the hemoglobin gene, so you’ll usually need to inherit two copies of this gene allele — one from each parent — to have the condition.
If you inherit one recessive allele from one parent but a dominant one from the other parent, you likely won’t have the condition. However, since you have one copy of the sickle cell allele, you are said to have the sickle cell “trait” and can pass this on to future generations.
Autosomal and sex-linked refer to the chromosome that the allele is present on.
Each cell of your body typically contains 23 pairs of chromosomes. In each pair, one chromosome is inherited from your mother and one from your father.
Chromosome pairs number 1 through 22 are referred to as autosomes and are the same no matter your sex.
The other pair of chromosomes is called the sex chromosomes. This pair differs depending on your sex. If you’re female, you’ll have an X chromosome from your mother and an X chromosome from your father. If you’re male, you’ll have an X chromosome from your mother and a Y chromosome from your father.
Some genetic conditions are sex-linked, meaning that the allele is present on the X or Y sex chromosome. Others are autosomal, meaning that the allele is present on one of the 22 pairs of autosomes.
The sickle cell anemia allele is autosomal, as it is found on
In order to have sickle cell anemia, you must have two copies of the recessive sickle cell allele. If you receive only one copy, geneticists refer to you as a “carrier.” This means while you have the sickle cell trait, you won’t have sickle cell anemia.
Your other allele will be dominant. Remember, the dominant allele usually overrides the recessive one, so carriers generally don’t have any symptoms of the condition. However, they can still pass their one copy of the recessive allele on to their children.
Here are a few example scenarios to illustrate how genes are passed on:
- Scenario 1. Neither parent has the recessive sickle cell allele. Their child will not have sickle cell anemia or be a carrier of the recessive allele.
- Scenario 2. One parent is a carrier while the other isn’t. Their child will not have sickle cell anemia. But there’s a 50 percent chance that children will be carriers.
- Scenario 3. Both parents are carriers. There’s a 25 percent chance that their child will receive two recessive alleles, causing sickle cell anemia. There’s also a 50 percent chance that they will receive one copy and be a carrier. Lastly, there’s also a 25 percent chance that their children won’t carry the allele at all.
- Scenario 4. One parent isn’t a carrier, but the other has sickle cell anemia. Their child will not have sickle cell anemia, but they’ll all be carriers.
- Scenario 5. One parent is a carrier, and the other has sickle cell anemia. There’s a 50 percent chance that children will have sickle cell anemia and a 50 percent chance they’ll be a carrier but not have the disease themself.
- Scenario 6. Both parents have sickle cell anemia. Their child will have sickle cell anemia.
If you have a family history of sickle cell anemia, but you don’t have it yourself, you may be a carrier. If you know others in your family have it, or you’re not sure about your family history, a genetic test can help determine whether you carry the sickle cell allele.
A doctor will take a small blood sample, usually from a fingertip, and send it off to a laboratory for analysis. Once the results are ready, a genetic counselor will go over them with you to help you understand your risk of passing the allele on to your children.
If you do carry the recessive allele, it’s a good idea to have your partner take the test as well. Using the results of both of your tests, a genetic counselor can help you both understand how sickle cell anemia may or may not affect any future children you have together.
Sickle cell anemia is a genetic condition that has an autosomal recessive inheritance pattern. This means that the condition isn’t linked to the sex chromosomes. Someone must receive two copies of a recessive allele in order to have the condition. People who have one dominant and one recessive allele are referred to as carriers.
There are various inheritance scenarios for sickle cell anemia, depending on the genetic makeup of both parents. If you’re concerned that you or your partner could pass the allele or condition on to your children, a simple genetic test can help you navigate all the potential scenarios.