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 -
X-Linked Recessive Inheritance
There are three major types of genetic inheritance: dominant, recessive and X-linked recessive inheritance. In order to discuss patterns of inheritance it is necessary to review how the genes on the chromosomes are passed on from parents to children. Everyone has 23 pairs of chromosomes. One member of each pair came from each parent. Twenty-two of the pairs are identical in shape and size; these are called the autosomes. One chromosome pair may be different; they are called the sex chromosomes because they determine the sex of the child. The sex chromosomes are called X and Y. Males have one X and one Y chromosome; females have two X chromosomes.
The Y chromosome contains the gene that determines that an individual will be a male; it has very few other genes. In contrast, the X chromosome has many genes. Some recessive traits caused by genes on the X chromosome include color-blindness, hemophilia, muscular dystrophy and some X-linked deafness syndromes.
Since a male has only one X chromosome, all the genes on his X chromosome, whether dominant or recessive, will be expressed because there are no corresponding genes on the Y chromosome. A female has two X chromosomes. If she has a recessive gene for deafness on one X chromosome and a normal gene on the other, she will have normal hearing. She is said to be a "carrier" for X-linked deafness. Rarely, a female will have the recessive gene on both of her X chromosomes, in which case she will be deaf.
When a female who is a carrier for X-linked deafness and a hearing male have children, all the daughters will be hearing because each daughter will receive a dominant normal X from the father. Each will have an equal chance of receiving the X with the gene for deafness or the X with the normal gene from her mother. Since males receive only one X and that is from the mother, each son will have an equal chance of being hearing or deaf.
When a man with X-linked deafness and a woman with two normal genes have children, all their daughters will be carriers because the father has only the one X to pass to all of his daughters. All their sons will be hearing because the father can only pass the Y to his sons.
Date Originally Created: Summer of 1989
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)