All About Genetic Testing

What is Genetic Testing?

Genetic testing is a laboratory-environment type of test that looks at a person’s genes or their specific DNA instructions as inherited from their parents. These types of tests have been known to identify a person’s increased risks of developing certain health problems.

It will be recalled that in 2013, news of Hollywood A-lister and UNHCR Ambassador Angelina Jolie’s preventive double mastectomy spread like wild fire. It was a decision she made after finding out that she carries a faulty copy of the BRCA1 gene, which put her at 87% and 50% chance of developing breast cancer or ovarian cancer respectively. Her own mother died from ovarian cancer and her grandmother and an aunt also died from cancer. With all these considerations at play, Ms. Jolie had her ovaries and tubes removed in 2015 as well.1

What Can We Learn From a Genetic Test?

That single genetic test identified a potential health risk for Ms. Jolie and helped in her choice of treatment. But what else are genetic tests good for? What else can we learn from them?

Apart from looking into potential health issues, a genetic test can help:2

  • Diagnose an existing disease
  • Identify the gene/s and the changes that happened to them to cause a disease previously diagnosed
  • Determine the seriousness of a disease
  • Guide doctors in choosing best course of treatment for a specific patient
  • Identify the changes that genes undergo which may increase the risk of developing a disease
  • Identify gene changes that may be inherited by children
  • Screen newborn babies for specific conditions that may be treated early on

Genetic Testing Methods3

  • Molecular Genetic Tests – This testing method looks at and analyzes short lengths of DNA or a single gene. By studying a single gene, a geneticist can observe and identify all changes or mutations in that gene that can potentially lead to a genetic disorder.
  • Chromosomal Genetic Tests–This testing method looks at and analyzes long lengths of DNA or whole chromosomes. Geneticists are able to observe large genetic changes, like an entire extra chromosomal copy that can result to certain genetic conditions.
  • Biochemical Genetic Tests – This testing method looks at and analyzes protein levels, specifically their 1) quantity and 2) level of activity. If either shows any abnormalities, they can result to changes in the DNA which ultimately results to certain genetic disorders.

 Common Clinical GeneticTests4

 

Name of Gene

Genetic Condition/Disorder

Why Do This Test

FMR1

Fragile X Syndrome

This genetic condition is the leading cause of inherited mental retardation.

F5

Factor V Leiden Thrombophilia

This inherited blood clotting disorder is the specific gene mutation that causes thrombophilia or a higher tendency to form abnormal blood clots that block blood vessels.

ABCC7

Cystic_Fibrosis

This progressive genetic disease causes persistent lung infections. It also causes damage to the kidneys, liver, pancreas and intestines.5

HFE

Hereditary Hemochromatosis

This disorder makes the body absorb too much iron from foods, eventually leading to what is commonly called Iron Overload Disorder.

HD

Huntington Disease

This is a progressive brain disorder that eventually leads to loss of cognition, emotional problems and uncontrolled movements.

DMD

Duchenne Muscular Dystrophy

This genetic disorder is caused by the absence of dystrophin. Dystrophin is a protein that helps to keep our muscle cells intact. Over time, this disorder leads to progressive muscle weakness and degeneration that mostly affects boys.

HEX-A

Tay-Sachs Disease

TSD is a fatal genetic disorder of early childhood that progressively destroys the nervous system. The absence of the enzyme hexosaminidase-A (Hex-A) causes a lipid called ganglioside (GM2) to build up in the cells, especially the nerves in the brain, subsequently damaging them.

BRCA1 & BRCA2

BRCA1 & BRCA2 Hereditary Breast Cancer

Specific inherited mutations in the BRCA1 and BRCA2 genes increase the risk of female breast cancer and ovarian cancers. These 2 genes produce tumor suppressor proteins that help fix or repair damaged DNA. Any mutation to these genes can prevent them from producing the required proteins or they produce malfunctioning proteins. Any DNA damage therefore remains unrepaired, making it more likely for them to develop more genetic alterations that can eventually develop into cancer.6

 

The Importance & Benefits of Genetic Testing

Imagine a child who actually has cystic fibrosis but was never screened for it as a newborn. That child would grow up seemingly chronically ill from respiratory infections – alternating between sinusitis, bronchitis, pneumonia or digestive problems like stomach pains or constipation one week and diarrhea the next. The child will suffer from poor growth and weight gain. The parents could be doing everything they can to keep their child healthy but without the knowledge that a genetic test could have given them when the child was born, they would keep grasping at straws. Should the child survive to adulthood, he/she will be facing reproductive health problems.

This is a single illustration of how important and helpful a simple newborn genetic test could have been for the quality of this child’s life. Had cystic fibrosis (CF) or other genetic disorders been identified when the child was born, the proper treatment and management could have been started as early as possible. While CF has no cure, treatments have improved over the years. They now include nutritional therapies, exercise and more effective medications, greatly improving the quality of life for CF sufferers and prolonging their life expectancy.

Apart from knowing about potential health problems and having the means to decide on the best course of treatment and make informed lifestyle changes, what other potential benefits can we gain from genetic testing?

  • Peace of Mind – A positive genetic test for any particular genetic disorder gives individuals a fighting chance at getting the proper treatments and therapies to manage their condition that they would otherwise keep wondering about if they didn’t have the test. A negative genetic test puts your mind at rest.
  • New Treatments – Geneticists are able to create new treatments based on their findings on which gene is mutated or from what the exact mutation within the gene is. This is particularly true in cancer treatment. They are able to design chemotherapies that are genetically tailored to a specific patient’s tumor. There are cystic fibrosis treatments for children who have a specific mutation in their CFTR gene. Genetic testing makes these kinds of personalized medicine within reach.7
  •  Family Affair – A genetic test could directly or indirectly impact the lives of other family members and help them make decisions for their future and/or the future of their children health-wise.  
  • Finding Roots – While a genetic test cannot magically produce one’s entire family tree, it helps establish blood/familial relations between people; it helps determine common ancestry; it helps build a profile of one’s ethnic origins.

Types of Genetic Testing

There are thousands of genetic tests available today that aid physicians in the diagnosis and treatment or management of many diseases, but there are general types of genetic tests that are done for the following reasons:

  • Preimplantation Testing – This type of testing is used on embryos that were created thru in-vitro fertilization. A small amount of cells from these embryos are tested for specific genetic changes that could result to disorders or abnormalities. Only embryos that show no genetic changes are eventually implanted into a woman.
  • Prenatal Testing - This type of testing is offered to parents-to-be if there is an increased risk of a chromosomal or genetic disorder for the fetus. For example, RB1 gene mutations can result to a baby being born with retinoblastoma which can destroy the baby’s vision shortly after birth. Knowing this beforehand prepares the medical team to begin treatment as soon as the child is born. Every day counts if the baby’s eyesight is to be preserved.
  • Newborn Screening – This type of testing is performed at birth and is used to identify genetic disorders that can be treated as early as possible. All states screen all newborns for phenylketonuria, a genetic disorder that can leave a child intellectually disabled if left untreated and congenital hypothyroidism.
  • Carrier Testing – This type of testing is used on people who have a family history of a certain genetic disorder and to those from ethnic groups predisposed to specific genetic conditions. This test can provide information if one or both parents can possibly pass on a genetic condition to any future children of the union.
  • DiagnosticTesting – This type of testing either identifies or rules out a specific chromosomal condition. In many cases, this test confirms a disorder that has already manifested itself thru physical signs and symptoms.
  •  Forensic TestingGenetic testing for forensic reasons uses DNA sequences to identify person for legal purposes. These legal reasons include:
  • Ancestry Testing -This type of testing, also called genetic genealogy is for people (families) who want to investigate their ancestry beyond the stories passed down thru generations or repeated at family reunions. There are 3 types of genetic testing used for genealogy:
  • Y-chromosome testing – This testing can only be done on male family members and therefore only looks at the direct male line. It is often requested to investigate possible connections between families of the same surname.
  • Mitochondrial DNA testing – This testing provides information about the direct female line and is especially useful because females lose their surnames upon marrying and female ancestors often get lost from historical records.
  • Single nucleotide polymorphism(SNP) testing – SNP patterns can approximate how much of a person’s ancestry belongs to a particular ethnic group. For example, an individual can be 50% European, 25% African, 20% Asian and 5% unknown.
  • Predictive & Pre-symptomatic Testing – These types of testing detect mutations in a person’s genes that are associated with late-onset genetic disorders. A family member may test positive for the disorder at the time of the test but have yet to display any physical manifestations, if ever. Having this information helps the patient make informed decisions about current and future medical care. Knowing these things help them make short-term and long-term decisions about many things that affect their lives - like selling the house by the beach to move to a condo in the city where medical facilities are more accessible or the other way around – sell the condo and move up the mountains for the quiet and the fresh air; to get married or not; to have a child or not; to do an Angelina Jolie and have a double mastectomy.

How is Genetic Testing Done?

A genetic test can be performed on the following samples:

  • Blood
  • Skin
  • Hair
  • Amniotic fluid
  • Other tissues

Collected samples are sent to a genetics laboratory where exact locations on the DNA chain are examined and analyzed for certain mutations that are associated with specific genetic conditions or disorders in defined population groups. Results are sent in writing directly to the patient if so requested or to said patient’s genetic counselor or doctor who ordered the test.

At-Home Genetic Testing

Traditionally, when some people have any reason to believe they may be at risk for an inherited disease, their path to getting a genetic test begins with a visit to their doctor. The doctor may then refer them to a genetic counselor who will closely study their family history. All the gathered information can be used to calculate their risk for the disease and that of other family members. Should one of the other family members already have some of the symptoms, they will be recommended to get genetic testing first. This will show if the disease was actually passed down or if it occurred just as it does for the rest of the population – “by chance”.8

The entire process all seems tedious at best, and some people simply want to get on with it, especially if their reason is other than to potentially find out about genetic disorders; like if they simply want to find out if they may be related by blood to another person; or if they are simply curious to learn about their ethnic origins.

This is where at-home genetic testing comes in. They are also called direct-to-consumer genetic testing and are sold directly to consumers through different marketing channels like the internet and print or TV Ads. Needless to say, they make a person’s genetic information accessible without having to go through a doctor or an insurance company first. The DNA test kit is mailed to the consumer, complete with instructions on how to collect the DNA sample, typically by swabbing the inside of the cheek. The sample is then mailed back to the laboratory. In some cases, the consumer is directed to visit a collection center to have some blood drawn. Results are either mailed, given over the phone or privately accessed online. The results are usually easy to understand, but there may also be a genetic counselor or healthcare professional available to provide more in-depth explanation of the results and answer questions.

  • Benefits of At-home Tests
    • Accessibility - Provides easy, no fuss access to genetic information without going through doctors or insurance companies.
    • Privacy & Convenience - Provides a convenient means of getting the process started in the privacy of your own home.
    • Peace of Mind – Some people are naturally more worrisome than others, strictly living by the adage “knowledge is power” and choosing to be prepared for any eventuality - for their own peace of mind. At-home genetic tests allows these individuals to do this. Regardless of the results, they would take whatever genetic information they will get and make future plans accordingly.
  • Available Tests

Thousands of genetic tests have been developed to aid physicians in their diagnosis. Some of these tests have been made available for the general population in the form of easy-to-use at-home testing kits. Some of the more popular tests include:

    • Legal DNA Testing – these at-home genetic DNA test kits are approved by and admissible in court.
      • Legal Paternity DNA Home Test Kit–A DNA paternity test determines the possibility that a certain male is biological father of a child. This test verifies 23 genetic markers in comparing the subject male’s DNA pattern against that of a child to determine if there is a match. This test uses a simple cheek swab from both the child and the subject male.
      • Legal Avuncular DNA Home Test Kit– Avuncular by definition means the relationship of a man and any of his siblings’ children. This test however covers either an uncle’s or an aunt’s likely biological relation to their sibling’s child. A child is half the genes of its biological father (or mother) and the father on average shares half of his genes with a full sibling. The laboratory counts the number of genetic matches and calculates the likelihood of the biological relation between the subject man or woman and the child, versus the likelihood of them being unrelated. This test uses a simple cheek swab from both subjects.
      • Legal Sibling DNA Home Test Kit – This home DNA test determines the statistical likelihood that 2 individuals share 2 parents (full-siblings), 1 parent (half-siblings) or no parent at all. This test is ideal if 2 people wish to find out if they share a father but he is not available to provide his own DNA sample. The test verifies 23 genetic markers in comparing both individual’s DNA patterns to determine if there is a match. This test uses a simple cheek swab from both alleged siblings.
    • Non-Legal DNA Testing – these at-home genetic DNA test kits are for the test subject’s peace of mind and are not legally approved by or admissible in court. 
      • Non-legal Paternity DNA Home Test Kit - A DNA paternity test determines the possibility that a certain male is biological father of a child. This test verifies 23 genetic markers in comparing the subject male’s DNA pattern against that of a child to determine if there is a match. This test uses a simple cheek swab from both the child and the subject male.
      • Non-legal Maternity DNA Home Test Kit – This test is ideal for establishing the biological relations between an alleged mother and her child especially for grown children who have been adopted as a child. The test uses a simple cheek swab from both subjects and verifies 22 genetic markers (STR loci) + amelogenin, the gender identification marker. Results are confidential and are available 2-3 days from the time the lab received the samples.
      • Non-legal Sibling DNA Home Test Kit – This home DNA test determines the statistical likelihood that 2 individuals share 2 parents (full-siblings), 1 parent (half-siblings) or no parent at all. This test is ideal if 2 people wish to find out if they share a father but he is not available to provide his own DNA sample. The test verifies 23 genetic markers in comparing both individual’s DNA patterns to determine if there is a match. This test uses a simple cheek swab from both alleged siblings.
      • Non-legal TwinZygosity DNA Home Test Kit – This test compares the DNA patterns of twins by looking at 23 genetic markers to establish whether they are indeed identical or fraternal. Zygosity testing can help determine if one twin’s health condition can possibly be experienced by the other. The test uses either a simple cheek swab or a blood spot sample (non-invasive collection). Results are available 3-5 business days from the lab’s receipt of the samples.
      • Non-legal Grandparent DNA Home Test Kit – A child’s DNA pattern may be compared to an alleged grandparent by looking at 23 genetic markers to determine if there is a match. This test uses either a simple cheek swab or a blood spot sample (non-invasive collection). Results are available 3-5 days from the time the lab received the samples.
      • Non-legal Avuncular DNA Home Test Kit - Avuncular by definition means the relationship of a man and any of his siblings’ children. This test however covers either an uncle’s or an aunt’s likely biological relation to their sibling’s child. A child is half the genes of its biological father (or mother) and the father on average shares half of his genes with a full sibling. The laboratory counts the number of genetic matches and calculates the likelihood of the biological relation between the subject man or woman and the child, versus the likelihood of them being unrelated. This test uses a simple cheek swab from both subjects.
    • Cancer Screening – this DNA Genetic Cancer Risk Test Kit examines 98 genes for mutations that are associated with 25 hereditary cancers. (see sample Gene-Cancer Matrix). Said genes are guideline-recommended by the ACMG (American College of Medical Genetics and Genomics) and NCCN (National Comprehensive Cancer Network). The DNA test kit includes a saliva collection tube, a set of instructions and all necessary requisition and consent forms that the testing lab will require. Results should be ready 3 weeks after the lab receives the sample. The results will include a personalized health risk management plan that the test subject can later review with his/her physician.
    • Weight Gene Screening – Five genes are known to affect the body’s ability to metabolize carbs and fats. They also have an effect on the body’s responsiveness to physical exertion. Results are available 10-14 business days from the time the lab received the sample. This Weight Control Genetic Home Test Kit looks at the following genes:
      • ADRB2-E27Q - Responsible for Sensitivity to Carbohydrates and Stress Impact
      • FABP2-T55A - Responsible for Fat Absorption and Insulin Regulation of Sugar
      • FTO - Responsible for Regulation of Metabolism and Satiety
      • MC4R - Responsible for Regulation of Satiety and Meal Frequency
      • SH2B1 - Responsible for Regulation of Insulin and Leptin Systems

 Risks and Limitations of Genetic Testing

With the usual cheek swab or blood spot samples required for genetic testing, there are practically no physical risks except perhaps in prenatal testing where a sample of the amniotic fluid is needed and where there is a small risk of a miscarriage. The actual risks from getting a genetic test done are more emotional, financial and social.

  •  Emotional because results, if bad, make people depressed or even angry. This not only affects the person who got tested, but their entire family as well, especially if the results make them all anxious about their own genetic predisposition to some diseases.
  • Financial because some of these tests, especially the more comprehensive ones can get pricey and are often not covered by insurance.
  • Social because of the possibility of genetic discrimination wherein a person who had a genetic test done are treated differently at work or by insurance companies simply because they may have a gene mutation that puts them at higher risk of an inherited disorder. Privacy is another major concern within the social context of risks when it comes to genetic testing. A person’s genetic information can very easily be compromised. Before sending out your DNA to a genetic test service provider, make sure you understand what they plan to do with your genetic information; whether your data will be shared with research companies; whether your genetic information can be linked back to your personal information, etc.9

Aside from all these risks, genetic testing also has its limitations. It only sounds like it but it is most definitely not the “be-all and end-all” of all diagnostic tools:

  • Limited information – genetic testing may be able to identify an inherited condition but it cannot predict whether the person tested will actually show symptoms of the disorder, how bad the symptoms will be or if the disorder will progress over time.10

Accuracy of Genetic Testing

There are 2 main measures of a genetic test’s accuracy, namely clinical validity and analytical validity. The quality of the test is further gauged by its clinical utility or simply put, how useful it is.

  • Clinical Validity – the genetic variant being analyzed should be well related to the presence or absence or risk of a particular disease.
  • Analytical Validity – the test should clearly and accurately detect the presence or absence of a specific genetic variant.
  • Clinical Utility – The test should be able to provide information about diagnosis, management, treatment or prevention of a disease. A test’s usefulness is often gauged by the consumer, the healthcare providers and/or insurance companies.

Genetic testing in itself is a major diagnostic breakthrough, with thousands of tests already developed as diagnostic tools for thousands of diseases. Consumers should make the effort to understand how genetic testing works and how they may take advantage of the kind of information they can get from one, whether they go the traditional route or opt to use an at-home genetic DNA test kit.

Sources:

1https://www.nytimes.com/2015/03/24/opinion/angelina-jolie-pitt-diary-of-a-surgery.html

2 https://www.genome.gov/19516567/faq-about-genetic-testing/

3https://ghr.nlm.nih.gov/primer/testing/uses

4 www.genomenewsnetwork.org/articles/01_01/common_tests.shtml

5 https://ghr.nlm.nih.gov/condition/cystic-fibrosis

6 https://www.cancer.gov/about-cancer/causes-prevention/genetics/brca-fact-sheet#q1

7 http://www.ihavelynchsyndrome.org/10-reasons-genetic-testing-important/#.WctxZ2iCzce

8 https://familydoctor.org/genetic-testing-what-you-should-know/

9 https://www.nbcnews.com/health/health-news/5-things-you-need-know-taking-home-genetic-test-n758816

10https://ghr.nlm.nih.gov/primer/testing/riskslimitations 

For Further Reading:

https://www.nbcnews.com/health/health-news/5-things-you-need-know-taking-home-genetic-test-n758816

https://hometestingblog.testcountry.com/?p=581

https://abouttesting.testcountry.com/2010/04/how-can-your-genotype-affect-your-weight-all-you-need-to-know-about-genotype-weight.html

https://abouttesting.testcountry.com/2012/06/three-common-methods-to-quantitate-dna-and-rna.html

https://abouttesting.testcountry.com/2010/04/all-you-need-to-know-about-eating-right-for-your-genotype.html

https://abouttesting.testcountry.com/2010/09/tribal-dna-test-how-different-american-indian-tribes-have-different-dna.html

https://www.testcountry.org/pros-and-cons-of-using-genetic-testing-for-the-best-weight-loss-diet.htm