Autosomal recessive inheritance

Autosomal-Recessive-inheritance-small-image

Used to describe a characteristic or condition that appears only in individuals who have received two copies of an altered gene, once copy from each parent.  People with two copies of the altered gene are called homozygotes.  Their parents, each with a single copy of the altered gene, appear normal and are called heterozygotes or carriers of the altered gene.

Autosomal recessive conditions

With an autosomal recessive condition, a gene alteration needs to be present in both copies of a particular gene to cause sufficient impairment to cell function to cause disease.  The alterations are located on an autosome.

A person with an autosomal recessive condition must have inherited one gene alteration from each parent.

In autosomal recessive inheritance, people with one copy of the gene alteration do not have the condition.  They are said to be carriers for the autosomal recessive condition.

AR-pedigree-example

Features of autosomal recessive inheritance that you may see on a family tree include:

  • males and females have the condition in roughly equal proportions
  • people with the condition are usually in one sibship in one generation
  • consanguinity, where both parents have one or more ancestors in common, increases the chance that a condition presenting in a child of theirs might be due to both parents being carriers for the same recessive gene alteration.

At conception each child of parents who are both carriers has a 1 in 4 (25%) chance of being an unaffected non-carrier; a 2 in 4 (50%) chance of being a carrier and a 1 in 4 (25%) chance of inheriting the condition.