GENETIC TESTING
Guide To: Predicting Your Chances of Developing a Disease

Genetic Tests

Genetic Testing

Genetic Testing

Contents

What Is Genetic Testing?
Types of Genetic Tests
Why Different Tests Are Offered
Online Internet Tests


Genetics Guide

Genetic Counselors
Genetic Disorders

Types of Genetic Tests

In Pregnancy
Before Pregnancy
PGD Testing (IVF)
Breast Cancer
Ancestry
Grandparents DNA
Siblings DNA
Twins DNA
Y Chromosome

What Is Genetic Testing?

Genetic tests identify the presence of certain genes or chromosomes which can predispose a person to medical problems or genetic disorders in the future. The results of these tests can confirm or rule out the presence of inherited disorders. Currently there are several hundreds of types of tests on offer. Genetic counselors usually help people decide which test is appropriate as well as discuss the pros and cons of testing including the emotional and social implications. Genetic testing before pregnancy can determine the likelihood of a child developing an inherited disorder from either parent. Genetic testing during pregnancy provides parents with information about their as yet unborn child. In adults, testing can help measure the risks of developing disease before symptoms start, such as breast cancer or type 2 diabetes. Other common tests which can be ordered directly by consumers without the involvement of a doctor include paternity tests and ancestry gene tests. Some DNA health tests which were formally only possible with the help of healthcare experts are also now available in supermarkets, for example those tests which can confirm cystic fibrosis carriers. Another clinic-based test which has received lots of media attention recently is nutrigenomic testing. It generally looks for multiple genes associated with common health disorders such as heart disease in women and men, diabetes and osteoporosis. Armed with the test results and information on a person's lifestyle and diet, a counselor can assess potential health risks.

Types of Genetic Tests

Gene Tests

These tests are used to check for a disease where someone has shown suspected signs, or to check if they are a carrier of the gene linked to the disease. Taking a sample of a person's blood, saliva or tissues, the DNA or RNA is checked for the presence of whatever gene is in question, or if any mutations have occurred within that gene. Relatively common genes tests include genetic tests for breast and ovarian cancer.

Chromosomal Tests

These tests look at the features of a person's chromosomes, specifically their number, structure and arrangement. They check if any chromosomes are missing, if they have changed shape or moved to a different chromosomal location. The most common type of chromosomal test is a Karyotype. This test gives a complete overview of someone's chromosome structure, from the largest down to the smallest. It is used for example in prenatal testing to determine if a baby has Down syndrome, which is caused by an extra copy of chromosome 21. A FISH analysis (fluorescent in situ hybridization) is even more detailed and can identify missing or extra chromosomes which may have been missed by a Karyotype. It can identify missing fragments of Chromosome 22 for example which is characteristic of velocardiofacial syndrome (VCFS), a condition which can cause heart defects and certain facial appearance effects.

Biochemical Tests

These test the activity levels of certain proteins in the body. As DNA, which is carried in the genes, contains the codes for making proteins, any abnormal amounts of proteins indicates something is not working correctly in the genes. These types of tests are most commonly performed on new born babies. For example, they can detect phenylketonuria (PKU), a genetic defect which can lead to a variety of health problems. People with the condition need to avoid foods high in protein or contain artificial sweeteners.

Why Different Tests Are Offered

Diagnostic Tests: For this purpose genetic testing is used to diagnose a disease or genetic condition, where a person is showing signs or symptoms. For example, if a baby is born with features that suggest Down Syndrome, a diagnostic Chromosomal test will confirm if the condition is present or not.

Predictive Testing: Also known as presymptomatic testing, this tests people who are prone to developing a disease - maybe because it runs in their family, or it is more common to their ethnical group. Predictive testing can help determine their likelihood of developing the disease at some time in the future. Genetic testing for breast cancer is one of the most popular tests in this category, although other cancers and type 2 diabetes tests are common as well. Predictive testing is carried out before any symptoms arise so it can lead to prevention and treatment recommendations. It is also used in families with Huntington's disease and Graves disease for example. Even though there is no prevention or treatment for Huntington's disease, a positive test result may help people come to practical decisions about careers, having families and insurance coverage. Cancer prevention or risk reduction on the other hand may be possible with certain preventative measures.

Carrier/Preconception Testing: This can tell people whether or not they are carriers of certain recessive genes linked to genetic disorders. This is most commonly offered to would-be parents before pregnancy. If one parent has a recessive gene, they will not get the disease, but they may pass it on to their offspring. If both parents are carriers, the likelihood of the child developing the disorder increases significantly. Common recessive disorders include Tay-Sachs disease and cystic fibrosis.

Newborn Screening: This is the most common type of genetic test and is applied to newborn babies. Using biochemical tests and blood samples, it screens for a variety of conditions from PKU to hearing and heart problems.

Prenatal Screening: Or genetic testing during pregnancy is sometimes offered to women experiencing a pregnancy after 35, where the risk of birth defects increases. It may also be offered to women from certain ethnic backgrounds or those with a history of genetic defects in the family. Three procedures are common in prenatal testing, these are chorionic villus sampling (CVS), amniocentesis test and pregnancy ultrasound scans. If the results are positive, the mother will need to decide if she wants to continue with the pregnancy or opt for a termination instead.

Pharmacogenetic Testing: The goal of this sort of testing is to determine how well a person's body will react to the use of certain medications. For example a test on patients with a certain type of leukemia can show if they would benefit or not from the use of the drug warfarin. Alterations in the CYP450 gene affects how people break down certain types of drugs. Pharmacogenetic testing helps ensure that people get the right sort of drugs and in the right amount for their personal genetic makeup.

Paternity Testing

If the father of a baby needs to be confirmed, paternity testing can be carried out, usually after the child is born. There are clinics around the States which can offer this service, or there are paternity test kits available online. It is not invasive and normally only involves taking a cheek buccal swab.

Direct to Consumer Internet Tests

There are a variety of genetic tests which are for sale over the internet - from health tests to ancestry and paternity tests. Health tests are used to check a person's predisposition to developing a disease. Most involve scrapping a few sample cells from inside the cheek and mailing the sample to a lab for analysis. The most common DNA Predisposition Tests sold this way check for conditions such as lupus, Graves disease, multiple sclerosis, Alzheimer’s, heart disease, osteoarthritis, atrial fibrillation, aneurysm and rheumatoid arthritis. The lab will normally return a personalized report within 2 to 4 weeks, noting each condition and your estimated lifetime risk of developing each one.

It must be remembered that many conditions, such as lupus and Alzheimer’s are not preventable, so knowing you are more prone to developing them may do nothing more than cause anxiety and depression. Also, for those conditions which may respond to preventative treatments, it is worth asking yourself if you are prepared to make the necessary lifestyle changes. If you discover that you have a higher risk of developing osteoporosis than the average woman, are you prepared to start exercising more, quit smoking and follow a healthier diet for life? If not, these tests are not much use to you. See osteoporosis prevention. In fact some health experts go as far to call direct-to-consumer genetic tests as 'modern day snake oil', insisting they provide little or no real-health information. In fact the CDC recently issued a fact sheet on the subject cautioning 'buyer beware'. Additionally a report by the Government Accountability Office raised concerns that these tests were misleading consumers by raising ambiguous health predictions. Although most manufacturer's of these tests advise users to discuss results with their family doctor, it is unclear how many actually do.

Nutrigenetic Tests: Companies who offer these tests claim that they can develop a specific diet plan based on your genetic makeup. A 2006 US Government report into these tests found them misleading and even dangerous as they have no scientific foundation.

Ancestry Gene Tests: Ancestral Origins Tests scan your genes and compare them to thousands of others on files from different anthropological regions around the world. As with other direct to consumer tests, these have not been scientifically proven.

Y Chromosome DNA Tests: This tracks the male lineage in a family, specifically the Y-chromosome which is passed down from father to son. There is also a maternal lineage test.

Twin DNA Testing: This helps twins discover if they are fraternal, identical or siblings.

Sibling DNA Tests: This test is to determine the probability of 2 siblings sharing the same set of parents. This may be carried out if one or both alleged parents are not available.

Grandparent DNA Testing: This test is often used in paternity cases where the alleged father is not available.

News: Scientists have just discovered 29 new genetic variants linked to multiple sclerosis (MS). This new information will help drug makers and scientists focus treatment on more specific areas of the immune system. Researchers also found that genes related to MS were linked to other autoimmune diseases such as type 1 diabetes and Crohn's disease.

  Related Articles on Genetics

For more links to genetics, see the following:

Paternity Testing During Pregnancy
Paternity Testing while Pregnant
Womens Health Questions

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