What is sickle cell anemia? Sickle cell anemia is a genetic condition that’s present from birth. Many genetic conditions are caused by altered or mutated genes from your mother, father, or both parents. People with sickle cell anemia have red blood cells that are shaped like a crescent or sickle. This unusual shape is due to a mutation in the hemoglobin gene. Hemoglobin is the molecule on 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, but not all, genetic conditions can be inherited from one or both parents. Sickle cell anemia is one of these conditions. Its inheritance pattern is autosomal recessive. What do these terms mean? How exactly is sickle cell anemia passed on from parent to child? Read on to learn more. Geneticists use the terms dominant and recessive to describe the likelihood of a particular trait being passed on to the next generation. You have two copies of each of your genes — one from your mother and another from your father. Each copy of a gene is called an allele. You may receive a dominant allele from each parent, a recessive allele from each parent, or one of each. Dominant alleles usually override recessive alleles, hence their name. For example, if you inherit a recessive allele from your father and a dominant one from your mother, you’ll usually display the trait associated with the dominant allele. The sickle cell anemia trait is found on a recessive allele of the hemoglobin gene. This means that you must have two copies of the recessive allele — one from your mother and one from your father — to have the condition. People who have one dominant and one recessive copy of the allele won’t have sickle cell anemia. 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. Out of each pair, one chromosome is inherited from your mother and the other from your father. The first 22 pairs of chromosomes are referred to as autosomes and are the same between males and females. The last pair of chromosomes are called sex chromosomes. These chromosomes differ between the sexes. If you’re female, you’ve received an X chromosome from your mother and an X chromosome from your father. If you’re male, you’ve received 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 autosomes. The sickle cell anemia allele is autosomal, meaning it can be found on one of the other 22 pairs of chromosomes, but not on the X or Y chromosome. In order to have sickle cell anemia, you must have two copies of the recessive sickle cell allele. But what about those with only one copy? These people are known as carriers. They’re said to have sickle cell trait, but not sickle cell anemia. Carriers have one dominant allele and once recessive allele. Remember, the dominant allele usually overrides the recessive one, so carriers generally don’t have any symptoms of the condition. But they can still pass the recessive allele on to their children. Here are a few example scenarios to illustrate how this might happen:
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 simple test can help to 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 that have one dominant and one recessive allele are referred to as carriers. There are many different inheritance scenarios for sickle cell anemia, depending on the genetics of both of the 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. Sickle cell anemia is a genetic disease, which means that it is caused by one or more genes not working correctly. Disease causing variants in the following gene(s) are known to cause this disease: HBB Answer What is a gene? Genes are part of our DNA, the basic genetic material found in each of our body's cells. Cells are the building blocks of all living things and specialized cells form our body's organs and tissues. DNA is found in the nucleus of a cell and, in humans, is packaged into 23 pairs of chromosomes with the help of special proteins. Each gene performs a different job in our cells. Some genes serve as the instructions to make proteins. Proteins are needed for the structure, function, and regulation of the body's cells, tissues, and organs. Some genes can turn other genes on or off. Others make RNA molecules that are involved in chemical reactions in the body. Sources to Learn More: What is a gene? (MedlinePlus) ; What's a Gene? (NHGRI) ; What are proteins and what do they do? (MedlinePlus) Genes are part of our DNA, the basic genetic material found in each of our body's cells. Cells are the building blocks of all living things and specialized cells form our body's organs and tissues. DNA is found in the nucleus of a cell and, in humans, is packaged into 23 pairs of chromosomes with the help of special proteins. Each gene performs a different job in our cells. Some genes serve as the instructions to make proteins. Proteins are needed for the structure, function, and regulation of the body's cells, tissues, and organs. Some genes can turn other genes on or off. Others make RNA molecules that are involved in chemical reactions in the body. Sources to Learn More: What is a gene? (MedlinePlus) ; What's a Gene? (NHGRI) ; What are proteins and what do they do? (MedlinePlus) What is a genetic variant? A genetic variant is a change in a gene's code or DNA sequence that causes the gene to be different than found in most people. A benign variant does not cause health problems or disease because the change does not affect how the gene works. A pathogenic variant does cause health problems or disease because the change does affect how the gene works. A pathogenic variant may also be called a mutation or a disease-causing variant. Variants can result from DNA copying mistakes made during cell division or certain environmental exposures. Variants that occur in the egg or sperm (germline mutations) can be passed on to offspring, while variants that occur in other body cells (somatic mutations) are not passed on. Sources to Learn More: What is a genetic variant and how do variants occur? (MedlinePlus); Definition of Variant (NCI); Mutation definition, illustration, and related terms (NHGRI) A genetic variant is a change in a gene's code or DNA sequence that causes the gene to be different than found in most people. A benign variant does not cause health problems or disease because the change does not affect how the gene works. A pathogenic variant does cause health problems or disease because the change does affect how the gene works. A pathogenic variant may also be called a mutation or a disease-causing variant. Variants can result from DNA copying mistakes made during cell division or certain environmental exposures. Variants that occur in the egg or sperm (germline mutations) can be passed on to offspring, while variants that occur in other body cells (somatic mutations) are not passed on. Sources to Learn More: What is a genetic variant and how do variants occur? (MedlinePlus); Definition of Variant (NCI); Mutation definition, illustration, and related terms (NHGRI) What is a genetic disease? A genetic disease is a disease caused by a change in part of a person's DNA. Genetic diseases may be caused by genetic changes in a single gene, in multiple genes, by a combination of genetic changes and environmental factors (multifactorial inheritance), or changes in chromosomes.Genetic diseases may be caused by genetic changes that are inherited from the parents and are present at birth, like sickle cell disease. Other genetic diseases present at birth may be caused by random genetic changes that happen while the egg or the sperm is forming or soon after fertilization.Some diseases, like many cancers, are caused by genetic changes that happen during a person's life. These are known as acquired or somatic cell genetic changes. Such genetic changes are not inherited from a parent, but happen either randomly or due to some environmental exposure (such as cigarette smoke). Sources to Learn More: Genetic Disorders (MedlinePlus) ; Genetic Disorders (NHGRI) A genetic disease is a disease caused by a change in part of a person's DNA. Genetic diseases may be caused by genetic changes in a single gene, in multiple genes, by a combination of genetic changes and environmental factors (multifactorial inheritance), or changes in chromosomes.Genetic diseases may be caused by genetic changes that are inherited from the parents and are present at birth, like sickle cell disease. Other genetic diseases present at birth may be caused by random genetic changes that happen while the egg or the sperm is forming or soon after fertilization.Some diseases, like many cancers, are caused by genetic changes that happen during a person's life. These are known as acquired or somatic cell genetic changes. Such genetic changes are not inherited from a parent, but happen either randomly or due to some environmental exposure (such as cigarette smoke). Sources to Learn More: Genetic Disorders (MedlinePlus) ; Genetic Disorders (NHGRI) All individuals inherit two copies of most genes. The number of copies of a gene that need to have a disease-causing variant affects the way a disease is inherited. This disease is inherited in the following pattern(s): Description Autosomal recessive inheritance Autosomal means the gene is located on any chromosome except the X or Y chromosomes (sex chromosomes). Genes, like chromosomes, usually come in pairs. Recessive means that both copies of the responsible gene must have a disease-causing change (pathogenic variant) in order for a person to have the disease. Mutation is an older term that is still sometimes used to mean pathogenic variant. A person who has an autosomal recessive disease receives a gene with a pathogenic variant from each of their parents. Each parent is a carrier which means they have a pathogenic variant in only one copy of the gene. Carriers of an autosomal recessive disease usually do not have any symptoms of the disease. When two carriers of an autosomal recessive disease have children, there is a 25% (1 in 4) chance to have a child who has the disease. Autosomal means the gene is located on any chromosome except the X or Y chromosomes (sex chromosomes). Genes, like chromosomes, usually come in pairs. Recessive means that both copies of the responsible gene must have a disease-causing change (pathogenic variant) in order for a person to have the disease. Mutation is an older term that is still sometimes used to mean pathogenic variant. A person who has an autosomal recessive disease receives a gene with a pathogenic variant from each of their parents. Each parent is a carrier which means they have a pathogenic variant in only one copy of the gene. Carriers of an autosomal recessive disease usually do not have any symptoms of the disease. When two carriers of an autosomal recessive disease have children, there is a 25% (1 in 4) chance to have a child who has the disease. |