Genetic Conditions

Learning about autosomal recessive inheritance

Genes are the instructions that tell your body how to develop and function. They are like a recipe for making cookies or the blueprints for a house.

You have 2 copies of almost every gene. One copy comes from the egg and one from the sperm that formed you. There are thousands of genes that are important for health.

We all have differences in our genetic instructions that make us different from each other. We call these variants. Many of these differences do not cause any health problems. These are called benign variants. But sometimes differences in our genetic instructions can cause health problems. These differences are called pathogenic variants or disease-causing variants. Genetic conditions can happen in different ways, including if you have a pathogenic variant in both copies of an important gene.

Autosomal recessive inheritance

Autosomal recessive inheritance refers to one way that a genetic condition can happen and how it can be passed down from parents to their children. The term autosomal means that the condition can affect anyone, no matter their gender or sex. The term recessive means that both copies of the gene need to have a pathogenic variant for the condition to happen.

With autosomal recessive conditions, if you have only 1 copy of a gene with a pathogenic variant, you do not have the condition. This is called being a carrier. For most genes, being a carrier does not have any personal health risks, but it does mean you can pass the pathogenic variant down to your children.

Autosomal recessive conditions

There are many different autosomal recessive conditions that can affect our health and development. Autosomal recessive conditions can affect people at different stages of their life. Depending on the condition, signs may be present during pregnancy or at birth, in childhood, in adolescence, or in adulthood. Autosomal recessive conditions may impact people in the same family differently.

Genetic testing for autosomal recessive conditions may or may not be available. In general, genetic testing may be considered for people with signs and symptoms of the condition. This is called diagnostic genetic testing. Genetic testing may also be considered if you have a family history of an autosomal recessive condition and you want to know if you might have a child with the condition. This is called carrier genetic testing. Carrier genetic testing is usually only done for adults over age 18. This is because there are no medical interventions for carriers, so testing does not usually need to be done in childhood.

How autosomal recessive conditions are passed down from parent to child

If 1 biological parent has the condition and the other is not a carrier

If 1 parent has an autosomal recessive condition, they have 2 copies of a gene with a pathogenic variant. If the other parent is not a carrier for the condition (unaffected), they have 2 copies of the same gene with no pathogenic variant. In each pregnancy, the child gets 1 gene copy from each of their biological parents’ pairs of genes.

This means that in each pregnancy where 1 parent has an autosomal recessive condition and 1 parent is not a carrier for that condition, the child will inherit 1 gene copy with a pathogenic variant and 1 gene copy without a pathogenic variant. The child will be a carrier of the condition but will not be affected by the condition.

If both biological parents are carriers

If both parents are carriers for the same autosomal recessive condition, they each have 1 copy of the gene with no pathogenic variant, and 1 copy of the gene with a pathogenic variant.

This means that in each pregnancy where both parents are carriers of the same autosomal recessive condition, there is a:

• 1 in 4 chance (or 25% chance) that the child will inherit 2 copies of the gene with no pathogenic variant (unaffected). They would not be at risk of having this condition and would not be a carrier of the condition.
• 1 in 2 chance (or 50% chance) that the child will inherit 1 copy of the gene without a pathogenic variant and 1 copy of the gene with a pathogenic variant. They will be a carrier of the condition.
• 1 in 4 chance (or 25% chance) that the child will inherit 2 copies of the gene with a pathogenic variant. Depending on the condition, they may develop the autosomal recessive condition or be at increased risk of developing the condition.

If 1 biological parent is a carrier and the other is not a carrier

If 1 parent is a carrier of an autosomal recessive condition, they have 1 copy of the gene with a pathogenic variant. If the other parent is not a carrier (unaffected), they have no pathogenic variants for that condition.

This means that in each pregnancy between 1 carrier parent and 1 unaffected parent, there is a:

• 1 in 2 chance (or 50% chance) that the child will inherit 1 copy of the gene without a pathogenic variant and 1 copy of the gene with a pathogenic variant. They will be a carrier of the condition.
• 1 in 2 chance (or 50% chance) that the child will inherit 2 copies of the gene with no pathogenic variant (unaffected). They would not be at risk of having this condition and would not be a carrier of the condition.

Parents cannot control what genes are passed on to their children

Having a genetic condition, or having a child with a genetic condition, is not caused by anything a person or parent did or did not do. The chance of inheriting an autosomal recessive condition is also not impacted by:

• the parent or child’s sex
• which parent has the pathogenic variant
• anything a parent did or did not do before or during pregnancy
• the outcome of a previous pregnancy (all pregnancies between the same 2 people will have the same chances of the child inheriting or not inheriting the autosomal recessive condition)

Genetic counselling

If you have any questions about autosomal recessive conditions or inheritance, talk with your healthcare team.

Genetic counselling is available for individuals who have a genetic condition, who may be at risk of a genetic condition, or who may have a family history of an autosomal recessive condition. A genetic counsellor can review your family history, genetic testing options, and screening options, and they can help families and individuals adjust to their diagnosis. Ask your healthcare provider if a referral for genetic counselling may be right for you.

To see this information online and learn more, visit MyHealth.Alberta.ca/health/aftercareinformation/pages/conditions.aspx?hwid=custom.ab_genetics_autosomal_rec_inherit_inst.

For 24/7 nurse advice and general health information call Health Link at 811.

Current as of: November 25, 2024

Author: Clinical and Metabolic Genetics Program, Alberta Health Services

This material is not a substitute for the advice of a qualified health professional. This material is intended for general information only and is provided on an "as is", "where is" basis. Although reasonable efforts were made to confirm the accuracy of the information, Alberta Health Services does not make any representation or warranty, express, implied or statutory, as to the accuracy, reliability, completeness, applicability or fitness for a particular purpose of such information. Alberta Health Services expressly disclaims all liability for the use of these materials, and for any claims, actions, demands or suits arising from such use.