More than 24,000 children are born with hearing loss in the United States each year. Boys Town National Research Hospital is a national leader in the diagnosis and treatment of children with moderate to profound hearing loss.
Information on Hearing Loss - Genetics and Deafness - Autosomal Dominant Inheritance
Genes are the basic unit of inheritance. They provide the instructions for growth and development of the single cell of a fertilized ovum into the complex structure of a baby. Many continue to provide instructions for the production of proteins needed for bodily functions throughout a person's lifetime. Genes are strung together like beads on a string and packaged into individual chromosomes. Chromosomes come in pairs; with one coming from an individual's mother and the other from the father. One pair of chromosomes is called the sex chromosomes, since they determine the sex of the individual; the other 22 pairs of chromosomes are called autosomes.
Since our chromosomes come in pairs, we have two copies of all of our genes. The two copies in a pair of genes may or may not have the same code. A gene that is expressed regardless of the code in the other gene is said to be dominant. An autosomal dominant gene is one carried on one of the 22 pairs of autosomes which means that males and females with the gene are equally likely to pass it on to male or female offspring.
A person who has a dominant hearing loss (HL) generally has one gene for HL and one normal gene in one pair of genes. In the diagram the gene for hearing loss is represented by a D and the normal gene by a d. The father is depicted as having one of each and the mother as having two normal genes. Obviously, the mother will always contribute a normal gene from that pair when they have children. There is a 50% chance the father will contribute the HL gene and a 50% he will contribute the normal gene.
There can be variation in the expression of a dominant gene even within the same family. In other words, the gene may cause a profound loss for an individual and only a mild to moderate loss for that individual's child. Another phenomenon that is seen with some dominant genes is nonpenetrance. This means that there is no detectable evidence that an individual with a dominant gene has the gene. When the gene is nonpenetrant it appears that the gene has skipped a generation. An example of this would be seen in a family with many people who are deaf including a child and a grandparent, but the intervening parent who has the same dominant gene for deafness, has normal hearing.
Date Originally Created: Fall of 1987
The information presented here first appeared in publications of the Boys Town National Research Register for Hereditary Hearing Loss, the National Institute on Deafness and Other Communication Disorders (NIDCD), Hereditary Hearing Impairment Resource Registry (HHIRR), or the Boys Town Research Registry for Hereditary Hearing Loss.
The Boys Town Research Registry for Hereditary Hearing Loss
The Boys Town Research Registry for Hereditary Hearing Loss (Registry) is designed to foster a partnership between families, clinicians and researchers in the area of hereditary hearing loss/deafness through three primary functions. First, the Registry disseminates information to professionals and families about clinical and research issues related to hereditary deafness/hearing loss. Second, the Registry collects information from individuals interested in supporting and participating in research projects. This information is used to support the third function of the Registry - matching families with collaborating research projects.
For more information, contact us at:
Research Registry for Hereditary Hearing Loss
555 N. 30th Street Omaha, NE 68131
800 320-1171 (V/TDD)
402 498-6331 (FAX)