Carrier (Heterozygous / Homozygous)
Definition
| Term | Meaning |
|---|---|
| Heterozygous | A variant is present in only one of the two copies of a gene |
| Homozygous | The same variant is present in both copies of a gene |
| Carrier | A person who carries a single copy of the variant for an autosomal recessive disease but is not affected |
Why it matters: In autosomal recessive inheritance, when each parent is a carrier (while both appear healthy), the chance of their child being born with the disease is 25% in each pregnancy. This is why carrier screening is an important part of preconception counseling.
What the patient should know: Being a carrier does not mean being ill. Carriers typically show no symptoms and lead normal lives. Carrier status matters only in terms of plans to have children, and even then the partner must also be a carrier.
In X-linked recessive diseases the situation is different: carrier females may show mild symptoms in some cases.