Autosomal Recessive Conditions

Topic Overview

Autosomal recessive conditions are genetic diseases that are passed to a child through both parents' chromosomes.

Each person inherits 23 chromosomes from each parent and so has 23 pairs of chromosomes. Each chromosome contains genes. One or both of the chromosomes in a pair may contain a changed (mutated) gene that could cause a genetic disease. In an autosomal recessive condition, both chromosomes in a pair must have a changed gene for the person to have the condition. If only one chromosome has a changed gene, the person is a carrier and does not have symptoms.

If both parents carry the gene change, there is a:

• 25% chance in each pregnancy that their child will inherit the changed gene from each parent (two genes) and have the condition.
• 50% chance in each pregnancy that their child will receive one changed gene and be a carrier.
• 25% chance in each pregnancy that their child will not receive the changed gene and be neither a carrier nor have the condition.

If only one parent carries the gene change, there is a 50% chance in each pregnancy that the child will:

• Receive the changed gene and be a carrier.
• Not receive the changed gene and be neither a carrier nor have the condition.

If neither parent carries the gene change, the child will not have this type of condition.

See a diagram of the chances of passing on an autosomal recessive condition.

Autosomal recessive conditions include Tay-Sachs disease, cystic fibrosis, sickle cell disease, autosomal recessive polycystic kidney disease (ARPKD), and phenylketonuria (PKU).