Usually, our bodies’ cells contain 23 pairs of chromosomes, which hold genetic information in the form of genes. Genetic disorders are caused by changes or damages to a gene, resulting in a genetic mutation. There are several ways in which a genetic disorder can be inherited, depending on the type of gene.
Autosomal Dominant Inheritance Patterns
Autosomal dominant genetic disorders occur through the inheritance of a single copy of a defective gene carried on one of the autosomes, or non-sex chromosomes. Dominant inheritance patterns can be inherited from just one of the two parents. If just one parent has just one affected chromosome, the child will have a 50% chance of inheriting the disorder.Examples of autosomal dominant genetic disorders are Huntington’s disease and Marfan syndrome.
Autosomal Recessive Inheritance Patterns
Recessive inheritance genetic disorders occur through the inheritance of two copies of the defective gene. It occurs when both parents are carriers of the same recessive disorder, with each parent carrying one of the mutated genes on the autosomes. The child would have to receive the affected chromosome from both parents, which translates to a 25% chance of inheriting the recessive genetic disorder. Typically, in recessive inheritance patterns, parents do not show signs of the recessive genetic disorder, and the mutation can skip generations. Therefore a child can receive one of the faulty genes and become a carrier of the genetic disorder, but won’t have the genetic disorder. Examples of recessive autosomal genetic disorders include cystic fibrosis and sickle cell disease.
X-Linked Inheritance Patterns
Some genetic disorders are caused by a mutation on the X chromosome, which is one of the sex genes. Females have two of the same kind of sex chromosome (XX), and males have two distinct sex chromosomes (XY). As the mutation only affects the X chromosome, and not the Y chromosome, only one affected copy of the gene is necessary for males to have the condition (who have one X chromosome in total). However, as females have two X chromosomes, both X chromosomes need to be affected for the disorder to manifest in females, so this type of disorder is more common in men. Some common examples of X-linked genetic disorders include hemophilia and color-blindness.
Other ways in which a genetic disorder can be inherited include:
- Y-linked inheritance, where a condition is caused by a mutation on the Y chromosome, and can only be passed from father to son (as females do not carry the Y chromosome). An example of this type of genetic disorder is Y chromosome infertility.
- Codominant inheritance, where two different versions of a gene are expressed, an example of this being individuals who have an ABO blood type.
- Mitochondrial inheritance, where there are mutations within the DNA of mitochondria (cell structures that convert molecules into energy) being passed on by females through their egg cells. An example is Leber hereditary optic neuropathy.
Learning More About Your Genetics
Even a healthy individual with no family history of a genetic condition may be a carrier of a genetic disorder, with one mutated gene and one healthy gene. For recessive disorders, it is possible to have genetic carrier screening. This can identify individuals with an increased risk of having children with certain genetic conditions. Genetic carrier screening can provide insight on chromosomal abnormalities and more. Non-invasive prenatal genetic testing can be a very important tool for those planning to start a family. Generally, the tests are performed before conception, using a blood or saliva sample. There hundreds of genetic factors and disorders that genetic carrier screening can evaluate.
Several factors increase the risk of having a genetic disorder, including family history, or belonging to an ethnic group with an increased risk of certain genetic disorders. Talk to your healthcare provider or a genetic counselor to learn more about genetic carrier screening.
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