Genetics of Hearing Loss
Certain causes of hearing loss are inherited (passed from parent to child). These types of hearing loss may be due to a change within one of the genes that are associated with hearing.
What are DNA, genes, and chromosomes?
"Every cell in our bodies contains DNA (the genetic information that tells our bodies how to grow and develop). DNA is packaged into genes. Genes come in pairs. We have pairs of genes that tell our bodies how tall we will be, what color our hair and eyes will be, and whether or not we have a higher risk of developing certain conditions, like diabetes or cancer."
Genes are packaged into larger units called chromosomes. Normally, every person has 23 pairs of chromosomes, for a total of 46. We receive half (23) of our chromosomes from our mothers and half (23) from our fathers. Because we receive one copy of each chromosome from our mothers and one from our fathers, we have two copies of each gene.
Sometimes, one or both of these genes may have mutations (changes which prevent the gene(s) from working normally). These gene changes can be inherited (passed from parent to child). It is important for parents to know that there is nothing anyone can do to cause or prevent a gene change from being passed to their child. A new mutation can also develop within a person’s DNA before he/she is born.
How can a person inherit hearing loss?
There are different inheritance patterns (or ways) for a person to inherit a genetic condition, including hearing loss.
Autosomal dominant inheritance
|For any condition that is inherited in an autosomal dominant pattern, a person only needs one copy of a gene change in order to have the condition. This gene change may come from either the mother or the father. Men and women are equally likely to have autosomal dominant conditions.|
Autosomal recessive inheritance
|For any condition that is inherited in an autosomal recessive pattern, a person needs to have two copies of a gene change in order to have the condition. In most cases, people with autosomal recessive conditions receive one gene change from their mother and one gene change from their father.
Parents of a person with an autosomal recessive condition may not have the same condition, since each parent only has one copy of the gene change. People who have one copy of the gene change are called carriers. Carriers do not have the condition, but are more likely to have children with the condition. Other family members (such as aunts, uncles, brothers, and sisters) may also be carriers.
Remember, humans normally have 23 pairs of chromosomes. One of these pairs is the “sex chromosomes.” The sex chromosomes determine whether a person will be male or female. Females have two X chromosomes. Males have one X chromosome and one Y chromosome.
We receive one sex chromosome from our mothers and one from our fathers. Because females only have X chromosomes, mothers always give an X chromosome to a child. Fathers can pass either an X chromosome or a Y chromosome to a child, since males have one X chromosome and one Y chromosome. If the father passes an X chromosome to a child, that child will be a girl. If the father passes a Y chromosome to a child, that child will be a boy.
Conditions that have an X-linked inheritance pattern are caused by changes within genes located on the X chromosome. Since men only have one X chromosome, each man who inherits the gene change will have the condition.
Women have two X chromosomes; they inherit one from their mothers and one from their fathers. If a woman inherits a gene change on an X chromosome, she will be a carrier. Carriers do not typically have a condition, but have a higher chance of having a child with the condition.
|Within our cells, we have tiny “powerhouses” called mitochondria which make energy for our bodies. Mitochondria are unique because they have their own type of genetic information, called mitochondrial DNA, as well as nuclear DNA. Certain genetic conditions are caused by changes within the mitochondrial or nuclear DNA found in the mitochondria.
Mitochondria are also unique because, unlike our chromosomes, we inherit all of our mitochondria from our mothers.