What is Genetics? : What is genetic testing?

What is genetic testing?

Genetic testing is a type of medical test that looks at a person’s DNA. Genetic tests are often used to diagnose or determine the type of disease a person has.

Genetic testing also can be used to determine if a person is a carrier of a disease or if they have a disease that is running through their family. There are many types of genetic tests. Some tests look directly at a specific gene, while others can look at the structure of the packages of our DNA (chromosomes). Genetic testing is typically ordered by a physician, often a geneticist. A geneticist is a specialized medical doctor who diagnoses and treats genetic syndromes.

Tests to diagnose a genetic condition

One of the main ways genetic testing is used it to diagnose a genetic condition. A person who shows signs or symptoms of a particular disease may need a genetic test for diagnosis. This is because the disease is caused by a change, or mutation, in the DNA. A physician, usually a specialist in genetics (a geneticist) orders these types of tests. Common tests for diagnosis are chromosome karyotype, chromosome microarray, or single gene tests.

A chromosome karyotype simply looks at the number and amount of chromosomes that a person has. Chromosome are the packages of DNA. Typically, humans have 46 chromosomes. However, some genetic conditions are caused by an increase or decrease in the number of chromosomes. Down syndrome is a genetic condition in which a person has an extra chromosome #21. Having this extra chromosome material causes the features of Down syndrome that include some level of intellectual disability, short stature, and problems with the heart at birth. A chromosome microarray is a genetic test that also looks at the chromosomes, but a microarray looks at the chromosomes in much greater detail. A microarray can determine if there are very small pieces of DNA added or missing in a person. There are many genetic conditions that are caused by these relatively small imbalances in the DNA.

A single-gene genetic test is a test that looks only at a specific gene that is associated with a known genetic condition. For example, we know that a genetic condition called Huntington disease (HD) is caused by the HD gene. Mutations in the HD gene cause a person to develop abnormal movements, problems with thinking and memory, and eventually leads to death. If a person has symptoms of HD, a geneticist will likely order a genetic test to look specifically at the HD gene to determine if there are any mutations in the gene.

Carrier testing

Carrier testing is a type of genetic test used to find out if a person is a carrier for genetic condition. Carriers of genetic conditions do not typically have symptoms associated with being a carrer. In fact, most people have no idea they are a carrier of a genetic condition. A person who is a carrier is called that because they do not themselves have the disease, but they are at risk of having children with the disease. Sickle cell disease is an example. Sickle cell disease is caused when a person has TWO mutations, one in each copy of a specific gene (the HBB gene). A person with sickle cell disease inherited one copy of the mutation from each of their parents. Their mom and dad, who did not have sickle cell disease, were carriers of the condition. If two parents are carriers for a genetic condition, there is a 1 in 4 (or 25%) chance each child can be born with the condition. There are many other diseases that a person can be a carrier for. The chances that someone is a carrier for one of these conditions often depends on their ethnicity. For example, a person of Puerto Rican decent has about a 1 out of 21 chance of being a carrier for a type of albinism called Hermansky-Pudlak syndrome, while a person of Northern European decent has about a 1 out of 29 chance of being a carrier for a disease called cystic fibrosis. When a couple is thinking about having children, it is important to talk to their doctor about whether they could be carriers for a genetic condition and ask about carrier testing.

Tests to determine risk for disease in the future

Some genetic tests are available to determine whether a person is a risk of developing a disease in the future. At this time, there are very few conditions that this type of testing is available for. These tests are typically offered to people who have a very strong family history of a condition, like colon cancer, breast cancer, or Alzheimer disease, but they don’t have the condition yet. It is often a very big decision whether to have testing like this done, since some people may not want to find out if they may develop a disease in the future that they don’t have yet. For some conditions, like Alzheimer disease, there is no known prevention or cure. For other diseases, there are steps that can be taken to prevent the disease if a person knows they are at risk. For example, genetic testing for the BRCA genes is available for women who have a strong family history of breast cancer. Women who have a mutation in one of the BRCA genes is at high risk (up to 80% over her lifetime) to develop breast cancer. It is recommended that women with a BRCA mutation starts screening much earlier than other women. In the future, genetic testing to predict someone’s risk for disease may be more commonly used by physicians. By doing genetic testing like this, a doctor may be able to determine someone’s risk for many common diseases and preventive actions can be taken. This is why it is extremely important to study the genetic causes of disease. If we understand what the genetic causes are, doctors can determine who is at risk for disease based on their genes.

Read on: What is Genetic Research?