Genetics Northern California

Autosomal Dominant

The term “autosomal” means that everyone, male or female, has two copies of that particular gene - one from their mother and one from their father.  “Dominant” means that a change in just one copy of the gene can lead to a genetic disorder or related medical problem. Some genes in our body need to have both copies working correctly. If even one copy is not working or is working differently than usual, it can lead to medical issues. 

How is an autosomal dominant condition inherited?
Many times an autosomal dominant condition is inherited from a parent. A person with a change (mutation) in an autosomal dominant gene has a 1 in 2 or 50% chance of passing the non-working gene to their offspring. Either a father or mother can pass an autosomal condition to a child.

Sometimes a dominant condition happens as a brand new mutation in a gene. The genetic term is a “de novo” mutation. A de novo mutation is usually the result of a random error in the DNA when an egg or sperm is being formed. The person with a de novo mutation is the first person in the family to have the condition. Even though the condition was not “inherited” from a parent, that person will have a 50% chance to pass it on.

Genetic terms that may be used related to an autosomal dominant condition:

  • Variable expressivity: In some genetic conditions, the same mutation in a gene can cause many different medical issues. Individuals may have no symptoms or be mildly affected by a condition; while others with the same mutation may have much more severe medical problems. This can result in family members with a wide range of symptoms, even when they all have the same autosomal dominant condition.

  • Reduced penetrance: Inheriting a mutation for an autosomal dominant condition does not always mean a person will have medical issues. For some dominant conditions, individuals can carry a mutation in the gene without ever developing any features of the disorder.

  • Gonadal mosaicism: This is rare. Most people with an autosomal dominant condition carry the disease-causing mutation in every cell of their body. However, a person can carry a mutation for a dominant disorder in just the egg or sperm cells and not in other cells of the body. This is called gonadal mosaicism. In a person with gonadal mosaicism most of the cells in their body have two working copies of the gene, so they do not have any features of the condition. But the DNA that is passed on to a child is the DNA found in the egg or sperm cells. A person with gonadal mosaicism can pass on a dominant condition to a child, even without having the disorder.

Last reviewed: February 13, 2015
Last updated: February 13, 2015

Reviewed by: Kaiser Permanente Genetics Department