Autosomal recessive disease

Autosomal recessive diseases 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 be defective in a way that causes a genetic disease. In an autosomal recessive disease, both chromosomes in a pair must have a defective gene for the person to have the disease. If only one gene is defective, the person is a carrier.

If both parents carry the gene, there is a:

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

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

• Receive the defective gene and be a carrier.
• Not receive the defective gene and be neither a carrier nor have the disease.

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

See an illustration of the chances of passing on an autosomal recessive disease.

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