Sickle cell is an inherited disease. Thus, a person who has sickle cell is born with it. Learning more about inheritance can help you understand how sickle cell and sickle cell trait are passed from parents to a child.
Genes usually come in pairs: one copy of a gene comes from each biological parent. This pair of genes is known as a genotype. Sickle cell disease is caused by inheriting two copies (one from each parent) of an altered HBB gene, which causes the production of an abnormal form of beta (β)-globin, such as hemoglobin S (HbS). Scientists have identified hundreds of variations in the HBB gene that cause abnormal beta-globin to form and cause disease. As a result, there is more than one type of sickle cell, which depends on the specific combination of alterations of the HBB gene you inherit. These different forms are described as your sickle cell genotype. Determining Inheritance ToolUse the interactive diagram below, called a Punnett square, to see the likelihood of a child inheriting a form of sickle cell disease or sickle cell trait. This Punnett square can help you see how genes can be passed from a parent to a child in every single pregnancy, regardless of the genotypes of previous children. Note that the “sickle cell disease” selection for this tool is for the most common type of sickle cell, hemoglobin SS. However, you can create your own Punnett square by following the format below and using a different genotype (such as hemoglobin SC or hemoglobin S beta-zero) in place of “SS”. Select a genotype (ie, AA, no sickle cell disease; AS, sickle cell trait carrier; or SS, sickle cell disease) for both the male and female, then select “View Results” to see the chances of a child inheriting sickle cell trait or sickle cell disease.
Male's
Female's
Chances of a child inheriting sickle cell trait or sickle cell disease for each individual pregnancy:
It is important to note that if one parent has an SS genotype, all of their biological children will have a genotype of AS at the very least. This means that their child will carry sickle cell trait and can pass the abnormal (sickle) HBB gene along to their own children.
As previously mentioned, there are hundreds of variations in the HBB gene that can cause abnormal beta-globin to form, and a genotype describes the alteration of the HBB gene that a person inherits from their parents. In other words, the genotype describes the type of sickle cell. The most common alteration in the HBB gene leads to the SS genotype. Other types of sickle cell are a result of inheriting one hemoglobin S gene and one different abnormal beta-globin gene. For example, inheriting one hemoglobin S gene and one hemoglobin C gene would result in an HbSC genotype. Some sickle cell genotypes are more common than others, with the severity of symptoms and complications varying across these different types.
If you're a carrier of sickle cell, it means you carry one of the genes that causes sickle cell disease, but you do not have the condition yourself. It's also known as having the sickle cell trait. People who carry sickle cell will not develop sickle cell disease, but may be at risk of having a child with sickle cell disease and may occasionally need to take precautions to stop them becoming unwell. You can find out if you're a carrier of sickle cell by having a simple blood test. GOV.UK has a detailed leaflet about being a sickle cell carrier. Anyone can be a carrier of sickle cell, but it's much more common in people from certain ethnic backgrounds. In the UK, most people who carry the sickle cell trait have an African or Caribbean family background. Screening for sickle cell disease is offered to all pregnant women in England, although most women will be at low risk and will not need to have a blood test to check if they're a carrier. Find out more about screening for sickle cell disease in pregnancy Anyone can ask to have a free blood test to find out if they're a carrier at any point. This can be useful if:
You can request the test from your GP surgery or nearest genetic counsellor, who'll discuss the result and implications with you if you're found to carry sickle cell. If you carry the sickle cell trait, you're at risk of having children with sickle cell disease, although this can only happen if your partner is also a carrier or has sickle cell disease themselves. If you're planning to have a child and you know you're a carrier, it's a good idea for your partner to be tested. If you and your partner both carry sickle cell, there's a:
If both of you are carriers and you're planning to have a baby, talk to your GP about getting a referral to a genetic counsellor, who can explain the risks to your children and what your options are. These include:
PGD is similar to IVF, but the resulting embryos are tested to check that they do not have sickle cell disease before they're implanted in the womb. The Human Fertilisation and Embryology Authority (HFEA) has more information about PGD. You're not at risk of developing sickle cell disease if you carry the sickle cell trait. The only time you may be at risk of health problems is in rare cases where you might not get enough oxygen, such as:
There's also a very small risk of developing kidney problems associated with carrying sickle cell. Apart from these uncommon situations, you can lead a completely normal and healthy life if you're a sickle cell carrier. People who are carriers of the sickle cell trait are also at risk of having a child with a blood disorder if their partner is a carrier of a different type of blood disorder. You can find more detailed information about some of the other types of carrier in these leaflets:
Page last reviewed: 16 April 2019 |
What are the chances that these parents will have two children with sickle cell trait and one with sickle cell disease?
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