Gene: A gene is a hereditary unit of DNA that is passed from parents to children. Genes contain instructions that tell the body how to grow and function properly. The human body is made up of trillions of cells that contain genes.
Transcript & Variant Nomenclature: The language used by labs to describe specific variants. This helps labs communicate clearly with each other and with ordering providers about test results.
Zygosity: Most genes come in pairs, with one copy of each gene coming from your mother and the other copy coming from your father. Zygosity refers to whether a person has a variant in one copy of a gene pair (heterozygous) or in both copies of a gene pair (homozygous).
- Some genes do not come in pairs. When a person has only one copy of a gene, that is called hemizygous, and these types of genes can also have variants. Hemizygous is often used to describe genes on the X chromosome in men, as men typically have only one X chromosome, while women typically have two.
- Genetic variants are generally present in all of the body’s cells. However, sometimes a variant is found in only some of the body’s cells. This is a mosaic test result.
Classification: A gene variant is classified by whether or not it is known to be disease-causing.
- Pathogenic/likely pathogenic refers to a gene variant that is expected to be associated with increased risk of disease.
- Variant of unknown significance refers to a gene variant where it is not known if it causes or does not cause disease
Disease: The condition or medical issue indicated by the gene variant.
Inheritance: The way in which a disease may be passed down from parents to children. You may see any of the following inheritance patterns listed on your report:
X-linked – X-linked conditions are caused by variants in genes found only on the X chromosome. Women typically have two X chromosomes, while men have one X and one Y chromosome.
- Most individuals with X-linked conditions are men who have a pathogenic/likely pathogenic variant on their X chromosome. Women who carry a disease-causing variant for an X-linked condition are usually not affected, as they have an additional copy of the gene on their other X-chromosome. However, sometimes women carrying X-linked variants exhibit symptoms of the condition. In this case, the symptoms are generally milder than those experienced by men who have the condition.
Autosomal – Autosomal conditions are generally caused by genetic variants found on autosomal, or non-sex-linked chromosomes. Most people have 22 pairs of autosomal chromosomes.
- An autosomal dominant condition occurs when a disease is caused by the presence of a single pathogenic/likely pathogenic variant. This means that it takes just one non-working copy of a gene to cause a disease. These diseases are usually inherited from one of the affected person’s parent or caused by a new mutation in the patient.
- An autosomal recessive condition occurs when a disease is caused by the presence of a pathogenic/likely pathogenic genetic variant on both copies of the patient’s gene. This means a person must have two non-working copies of a gene to have a disease. In these disorders, the affected person’s parents are usually unaffected carriers who each have one copy of the pathogenic/likely pathogenic genetic variant and one normal gene.