among the Deaf
In the United States, at least 85% of individuals with profound deafness marry another deaf person. There are few other genetic traits for which such a high degree of assortative mating (like marrying like) has been described.
Families in which there have been many generations of deaf marrying deaf make determining the chances that parents will have deaf children difficult because several different genes for deafness may be present in the family. One reason why this has not lead to a major increase in the frequency of deafness is because of the extreme degree of heterogeneity that exists among the many different forms of genetic deafness.
In the case of marriages between couples who both have recessive deafness, the chance they will have deaf children can range from close to zero to 100%. If both partners have the same form of recessive deafness, all of their children will be deaf. This situation occurs in only about 5% of all marriages among the deaf. If the parents have different types of recessive deafness, all the children can be hearing. In about 80% of marriages among the deaf, all of the children are hearing.
Finally, a deaf couple can have both deaf and hearing children if at least one has a dominant form of deafness or if one parent is a carrier of a recessive deafness gene for which the other parent has a “double dose.” As progress is made in identifying the specific genes and genetic changes that can cause deafness, it will be possible to specify a couple’s chances with greater precision.
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