Carrier test for autosomal recessive diseases

Diagram of recessive gene transmission from parents to child

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Autosomal recessive diseases are genetic diseases that are passed to a child through both parents' chromosomes. Autosomal recessive diseases include Tay-Sachs disease, cystic fibrosis, sickle cell anemia, autosomal recessive polycystic kidney disease (ARPKD), and phenylketonuria (PKU).

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 can carry a mutation and be abnormal or 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 of the disease but does not have any symptoms.

Carrier test information for autosomal recessive diseases
One parent is a carrier Both parents are carriers

If only one parent carries the abnormal gene, there is:

  • A 50% chance in each pregnancy that their child will receive the defective gene and be a carrier.
  • A 50% chance in each pregnancy that their child will not receive the defective gene and will not be a carrier or have the disease.
  • No chance (0%) that their child will have the disease.

If both parents carry the abnormal gene, there is:

  • A 25% chance in each pregnancy that their child will inherit the defective gene from each parent (two genes) and have the disease.
  • A 50% chance in each pregnancy that their child will receive one defective gene and be a carrier.
  • A 25% chance in each pregnancy that their child will not receive the defective gene and will not be a carrier or have the disease.

Note:

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

Last Updated: November 4, 2009

Author: Maria Essig

Medical Review: Kathleen Romito, MD - Family Medicine & Siobhan M. Dolan, MD, MPH - Reproductive Genetics

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