A genetic variant is a change in a gene’s DNA sequence. Specifically, variants affect nucleotides, the building blocks of DNA. However, the changes they cause do not necessarily result in disease. For this reason, mutation, the older term for variant, has fallen out of favor as the negative connotations associated with the term do not accurately reflect reality.
There are two types of gene variants:
Germline Variants: These are hereditary variants present in egg and sperm cells, also called germ cells. They are passed down from parents to offspring. Hereditary variants are present in every cell of the growing fetus and remain with us throughout our lifetimes. They are responsible for traits such as eye color and blood type, as well as for genetic diseases, such as sickle cell anemia, and the propensity for certain conditions, such as high blood pressure.
Somatic Variants: These are variants that occur in our cells during cell division. They take place after conception, at any time during our lifetime, and they affect only somatic cells (those that are not egg or sperm cells). For this reason, they are not passed on to offspring. Somatic variants can be caused by environmental factors, such as radiation from the sun or cigarette smoke. They can also arise during cell division when DNA miscopies itself. Since all of our cells divide and copy themselves constantly, the affected cell will pass on the variant to every cell that forms from it.