MEDICAL GENETICS :: Single Gene Defects
Autosomal Recessive: Cystic Fibrosis, Sickle Cell Anemia, Tay Sachs Disease
Genes are inherited from our biological parents in specific ways. One of the basic patterns of inheritance of our genes is called autosomal recessive inheritance.
What is autosomal recessive inheritance?
Autosomal recessive inheritance means that the gene is located on one of the autosomes (chromosome pairs 1 through 22). This means that males and females are equally affected. "Recessive" means that two copies of the gene are necessary to have the trait, one inherited from the mother, and one from the father. A person who has only one recessive gene is said to be a "carrier" for the trait or disease, but they do not have any health problems from "carrying" one copy of the gene. Most people do not know they carry a recessive gene for a disease until they have a child with the disease. Once parents have had a child with a recessive trait or disease, there is a one out of four, or 25 percent chance, with each subsequent pregnancy, for another child to be born with the same trait or disorder. This means that there is a three out of four, or 75 percent chance, for another child to not have the trait or disease:
The birth of a child with a recessive condition is often a total surprise to a family, since in most cases, there is no previous family history of a recessive condition. Many autosomal recessive conditions occur this way. As mentioned above, a person who "carries" one copy of an autosomal recessive gene is usually not aware they carry the gene, because they do not show any signs of the disease or condition. It is estimated that all people carry about five or more recessive genes that cause genetic diseases or conditions. Usually a person does not know they carry a recessive gene unless they have the disease in their family, or if they have had an affected child.
What are autosomal recessive disorders?
Mutations (or changes in the DNA that codes for a gene) have occurred over time in different parts of the world. Anyone can carry virtually any type of recessive gene; however, there may be certain ethnic groups more likely to carry certain recessive genes, because of where the mutation originated. For example, the gene which causes Tay Sachs disease is found most commonly in persons of Ashkenazi Jewish descent (because the mutation is thought to have originated in this area of eastern Europe), but can also be seen in persons who are not Ashkenazi.
What are some of the different types of autosomal recessive disorders?
Examples of autosomal recessive disorders include cystic fibrosis, sickle cell anemia, and Tay Sachs disease.
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