We already know that one of the causes of rhinorrhea is hereditary hemorrhagic capillary dilation, which is an autosomal dominant disorder. Most patients have parents who also have this disease. The children and siblings of the pre-documented (the first patients found in the family) have a 50% chance of inheriting this disease-causing mutation. So what is dominant inheritance?
The following will give you information about what dominant inheritance means and how dominant genetic disorders are inherited. In order to understand what dominant inheritance is, it is helpful to first understand genes and chromosomes.
Genes and chromosomes Our bodies are made up of millions of cells. Most cells contain a whole set of genes. We humans have tens of thousands of genes. Genes are like a series of instructions present in the body that control our growth and the proper functioning of our bodies. Many of our physical characteristics, such as eye color, blood type, or height, are controlled by genes.
Genes are found on thread-like chromosomes. Typically, most of our cells contain 46 chromosomes. We get our chromosomes from our parents, 23 from our mother and 23 from our father, so we have two sets of 23 chromosomes each, or we have 23 pairs of chromosomes. Because chromosomes are made up of genes, for most genes we get two copies of it through inheritance, one from the father and one from the mother (i.e., genes exist in pairs). This is the reason why we often share the same characteristics as our parents. Chromosomes are made up of a chemical called DNA, and furthermore, so are genes.
There are times when a change (mutation) in one copy of a gene will prevent it from working properly. When the mutation occurs in only one copy of a pair of genes and the other copy is normal, and the mutated copy is in a recessive state, it usually does not cause a genetic problem.
What is autosomal dominant inheritance?
Some genetic disorders run in families in a dominant fashion. This means that a person inherits a normal copy of the gene and a diseased copy. However, the diseased gene is dominant and suppresses the normal copy. This causes the individual to have a certain genetic disease. The genetic disorder that an individual has that is determined by the mutated gene is called a sexually transmitted disease.
Some dominant genetic disorders affect individuals at birth. Others only become affected in adulthood. These are called late-onset disorders.
How are dominant genetic disorders inherited?
Below: How are dominant genetic disorders passed from parent to offspring?
When a patient has a diseased gene, he passes on one of his normal or diseased genes to his children. Thus, each child has a 50% chance of inheriting the altered gene and developing the genetic disorder.
There is also a 50% chance that the child will inherit the normal gene. If this happens, the child will not have the disease and will not pass the altered gene on to any of his/her children.
These possible outcomes occur randomly. The odds of this are the same for each pregnancy, and for boys and girls.
Why does a genetic disorder sometimes not occur in one generation?
Some dominant genetic disorders affect family members very differently. This is called variable expression. This genetic disorder is not really missed in the current generation, but some people have very mild symptoms so that it looks like they don’t have the disease. They may not even know that they have the genetic disorder.
In late-onset genetic diseases (those that manifest in adulthood, such as hereditary breast cancer and Huntington’s chorea), people may die for some unrelated reason before the genetic disease is present, or they may never be given the correct diagnosis.
However, the parental generation may pass on this genetic disease to the offspring.
What if a person is the first person in the family line to have a certain genetic disorder?
A person who is born with a dominant genetic disorder can be the first person in the family to have that genetic disorder. This can happen because he develops a new genetic mutation that is present in the sperm or egg cells that created the child. When this happens, the parents of the child do not have the disease. Parents have a strong desire not to have another child with the same genetic disease, but you should always discuss this risk with your doctor. However, a sick son or daughter with a diseased gene can pass on the diseased gene to his/her child.
For certain dominant genetic disorders, it is possible to test during pregnancy to determine if the baby has inherited the disorder (see the “Amniocentesis and Chorionic Villus Testing” flyer for more information on these tests). These are some of the things you should discuss with your doctor and health care professional.
Other family members If someone in your family has a dominant genetic disorder, you may want to discuss this with other family members. This information may be helpful to other family members in making a diagnosis. This information is especially important for those family members who already have children or want to have children.
Some people find it difficult to tell other family members about a genetic disorder.
They may be concerned about causing anxiety in the family. In some families, people lose contact with other relatives and find it difficult to reach them. Geneticists have a lot of experience with these families and can help you in discussing the situation with other family members.
The main point to keep in mind is that a person with a dominant genetic disorder only needs to inherit one altered gene (50% chance). These results occur randomly. The chances are equal for each pregnancy and for both boys and girls.
The mutated gene cannot be corrected for the rest of your life. The diseased genes are not contracted from someone else. For example, they can still be used as a blood donor.
People often feel guilty about inherited diseases that run in their families for generations. Remember it is not the fault of any one person and no one did anything to cause it to happen.