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).
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.
Chromosome with
retinal degeneration gene
Chromosome with normal gene
