The Inheritance of Retinal Degenerations

Page 4

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Autosomal Recessive

In an autosomal recessive retinal degenerative disease, the affected person has two copies of the altered gene. These genes lie on one of the 22 pairs of autosomes. Each of the affected person's parents has one altered gene paired with one normal gene and is called a carrier. Carriers do not have the disease. Autosomal recessive RP is documented in about 30 percent of all families with RP.

When two carrier parents have children, each parent will pass on either the altered ger or the normal gene. When both parents pass on the altered gene, the child will have two copies of the mutated gene and will have the disease. There is 1 chance in 4, or a 25 percent chance, that each child will have the disease. If one parent passes on the altered gene and the other parent passes on the normal gene, the child will be an unaffected carrier like the parents. There is 1 chance in 2, or a 50 percent chance, the each child will be a carrier. And if both parents pass on the normal gene, the child will not be affected and will not be a carrier. There is 1 chance in 4, or a 25 percent chanc that each child will neither have retinal degeneration nor be a carrier (Figure 6).

Figure 6, Autosomal Recessive
Figure 6. Autosomal recessive retinal degeneration
Affected Chromosome Chromosome with retinal degeneration gene Unaffected Chromosome Chromosome with normal gene


When a person with an autosomal recessive RP wants to have children, he or she is often concerned about passing on the disease. If the affected person's partner is not blood relative (for example, a cousin), does not have the same autosomal recessive and has no affected relatives, the chance that the partner will be a carrier of an autosomal recessive RP gene is about 1 in 80, and the chance that the couple will have a child with RP is less than 1 percent (1 in 100). For retinal degenerations other than RP, the chance that the partner will be a carrier of an autosomal recessive retinal degeneration gene and the chance that the couple will have a child with that retinal degeneration may vary somewhat.


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Date last modified December 4, 1998