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Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Conclusion
  5. References

The clinical applications of genetic testing are growing rapidly and they now account for a significant percentage of total laboratory testing procedures. Many clinicians are uncomfortable with the types and applications of genetic tests and the dependable resources that are available for self-education. Furthermore, Direct to Consumer genetic testing has presented several challenges to healthcare providers as consumers now have an access to tests that they may not fully understand and results they may act upon inappropriately. This article presents some of the issues and resources to help nurses navigate this changing landscape.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Conclusion
  5. References

The use of genetic and genomic testing for clinical decision-making is increasing exponentially. It is difficult to know exactly how widespread genetic testing is because no databases currently capture this information. We can, however, extrapolate from data kept by insurers. For example, United Healthcare (2012), estimates that the cost of genetic testing for its members was approximately $500 million in 2010. They note that 40% of these tests were for infectious diseases, 16% for cancers, and 44% for all other disorders. Combining these data with Medicare and Medicaid data, they estimate national spending on genetic testing was $5 billion in 2010, and they project that it will increase to between $15 billion and $25 billion by 2021 (United Healthcare 2012). Genetic testing is big business and chances are very good that your patients or their families will receive some type of genetic testing in the near future.

Consumers tend to have positive attitudes toward genetic testing, however, in a survey of nearly 3,000 consumers only 6% reported having had a genetic test themselves and 3% were uncertain about whether or not they had such a test (United Healthcare, 2012). Only 7% of physicians describe themselves as “very knowledgeable” about genetic tests, while 75% say that they are “somewhat knowledgeable.” That leaves close to 20% of physicians who were willing to report that they know little about genetic tests (United Healthcare, 2012). Genetics and genomics information has only been included as part of the essential education for baccalaureate degree nurses since 2008 (American Association of Colleges of Nursing, 2008). Little is known about practicing nurses' knowledge of genetic testing. Clearly much education of both consumers and healthcare professionals in called for.

One of the problems with achieving a well-educated workforce is the rapidly changing landscape for genetic testing and the confusion that ensues when nongenetic tests (no DNA involved) are used to diagnose genetic disorders. When a biochemical measurement determines whether or not a person has an inherited disease, is that a genetic test? For example, some cases of cystic fibrosis (CF), a disease that is transmitted in an autosomal recessive manner, are diagnosed using a sweat chloride test. This genetic disease can be diagnosed without testing genetic material! It will be helpful to review the types and range of genetic tests in common use.

There are currently genetic tests for more than 2,500 diseases. Nearly 2,300 are available for use in clinical practice, while the remaining tests are offered to participants in research studies (GeneTests, 2012). However, the number of tests is rapidly increasing. Both healthcare professionals and consumers can get up-to-date information about what genetic tests are available, expert authored reviews of genetic diseases, and a directory of genetic services including locations of laboratories and genetic counselors from the website http://www.ncbi.nlm.nih.gov/sites/GeneTests/ (see Figure 1). Educational information about genetic testing, genetic consultation, and ordering a genetic test is also available as well as slide presentations which can be downloaded and links to other online resources. “GeneTests” is an invaluable resource, funded by the National Center for Biotechnology Information (NCBI) and sponsored by the University of Washington.

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Figure 1. Screen capture of GeneTests.org Home Page. Used with permission: GeneTests Medical Genetics Information Resource (database online). Copyright, University of Washington, Seattle. 1993-2012. Available at http://www.genetests.org.

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Types of genetic tests

There are three major types of genetic tests: biochemical, cytogenetic, and molecular.

Biochemical Tests

Biochemical tests entail laboratory evaluation of gene products such as enzymes, hormones, or metabolites. When a gene coding for an enzyme is defective, the quantity or quality of the enzyme produced will be altered. Therefore, we can test an enzyme level in the blood and, if the enzyme is extremely low or not present at all, we can conclude that a likely cause is a problem with the gene that codes for that enzyme. This kind of testing is used commonly to screen for phenolketonuria (PKU) or Tay Sachs disease. Although these conditions are often diagnosed in childhood, with enzyme replacement therapy or dietary modifications, many patients are living well in their adulthood (Beery & Workman, 2012).

Cytogenetic Genetic Tests

Cytogenetic tests examine chromosomes and evaluate their number and structure. Humans have 23 pairs of chromosomes, 22 autosomes, and 2 sex chromosomes (X and Y). One member of each pair comes from the father and the other member comes from the mother. Sometimes mistakes are made in the process of cell division that produces the egg or sperm (meiosis). This can result in extra chromosomes once the egg is fertilized, as seen in Down syndrome (trisomy 21), or absent chromosomes, as seen in some cases of Turner syndrome (X0).

Molecular Genetic Tests

Molecular genetic tests are probably what most people think of when they talk about genetic testing. In molecular testing, technicians are looking for changes (mutations) in DNA or RNA. Specific genes may be evaluated to make sure that the sequence of DNA bases is the same as a reference sequence. Once changes are noted, it must be established that the change is deleterious, that is, associated with a disorder.

Fluorescence in situ hybridization

A technique called Fluorescence in Situ Hybridization (or FISH) tags areas of interest on either whole chromosomes or parts of chromosomes with a fluorescent signal. For example, if you are interested in knowing whether or not a person has an extra Y chromosome, you can create a fluorescently labeled probe (string of matching DNA sequences) that will bind to the Y chromosome making it glow when seen under a special microscope. If you see two glowing chromosomes there are two Y chromosomes present. Most men have one X and one Y chromosome (XY). Most women have two X chromosomes and no Y chromosomes. However, there can be variations, as seen in males with XYY syndrome (Beery & Workman, 2012). This type of testing would be considered molecular cytogenetic testing because chromosomes are being evaluated using a molecular technique.

Sometimes chromosomes break and reconnect to other nonmatching chromosomes (e.g., chromosome 9 breaks and part of it exchanges with part of chromosome 22, which has also broken). This is called a translocation. For example, in chronic myelogenous leukemia (CML) a translocation between chromosomes 9 and 22 can often be seen in cells of the bone marrow. This is sometimes called the Philadelphia chromosome. Evaluation of chromosome pieces is somewhat of a cross between cytogenetic and molecular genetic testing.

Applications of genetic tests

Genetic testing can be used in several ways. When a patient is thought to have a genetic disease based on clinical signs and symptoms, but the clinician is not sure, a genetic test may be ordered to confirm or refute the diagnosis. This is called diagnostic genetic testing. An example would be when a person has some of the physical characteristics of Marfan syndrome (tall with long fingers and toes), but the clinician is uncertain about whether or not the patient actually has the disease. A diagnostic genetic test could be very helpful in this case.

Predictive Genetic Tests

Predictive genetic tests come in two varieties. Both are used to test asymptomatic people who have a risk of genetic disease based on their family history. The test is considered Pre-symptomatic when a positive result would indicate that the person will almost certainly get the disease. For example, when a person tests positive for Huntington disease, he or she will eventually become sick unless they die of something else first. A predispositional genetic test will identify someone who has a greater risk than someone from the general population for developing the disease in the future. For example, if a person tests positive for a disease-causing mutation in the tumor suppressor genes BRCA1 or BRCA2, he or she has a lifetime risk of developing breast cancer that far higher than that of the general population, but it is not 100%. There is still a chance that this patient will fall in the smaller group of people who carry a potentially deleterious mutation but do not get sick (BRCA1 BRCA2, 2009). Therefore, testing positive for a disease-causing BRCA1 or BRCA2 mutation indicates increased susceptibility or a predisposition to get the disease.

Carrier Tests

Carrier Tests are used when a person has a family history of a recessive genetic disease and wants to know if he or she would be able to pass the disease on to his or her children. Carrier tests are often used for asymptomatic couples who want to have children, but are concerned because they have relatives with an autosomal recessive disease such as cystic fibrosis. If each member of a couple is found to be a carrier (heterozygous) for a mutation that can cause cystic fibrosis, the risk that their offspring would have the disease would be about 25% for each pregnancy. Some couples prefer to know this information before they get pregnant. Some may choose to use reproductive technologies such as preimplantation genetic diagnosis to greatly increase the likelihood that they will have a healthy baby (Beery & Workman, 2012).

Dose response genetic testing

Dose Response Genetic Testing is used to predict how a person will respond to a drug. Pharmacogenomics provides clinicians with data on variations in metabolizing enzymes, transporters, and receptors which could alter the blood levels of a drug prescribed to treat a given condition. If we were able to identify how well a drug would be metabolized or transported by an individual, we could reduce both adverse drug reactions and cases of therapeutic failure. We are in the era of personalized or precision medicine, where the right therapy can be selected and applied at the right dose for the right patient. While we are seeing more and more applications of pharmacogenomic information, this science is still in the early stages of clinical use (Beery & Workman, 2012).

Direct to consumer genetic testing

Genetic tests that are marketed to the general public are referred to as Direct to Consumer Genetic Tests (DTC). Much concern has been expressed in the scientific community about the validity of these tests and the ethics of offering them directly to consumers without referral by healthcare professionals or, in many cases, without any pretest or post test counseling by genetics professionals.

Types of DTC tests

There are two different types of DTC genetic tests. The first tests are the same as those offered from medical providers. They are diagnostic, predictive, or carrier tests that have been shown to have some clinical validity, which is defined as being both accurate and reliable in predicting the risk of the disease of interest (Mihaescu, Meigs, Sijbrands, & Janssens, 2011). The second type tests for the presence of gene variants that have been associated with complex or polygenic diseases. These are diseases for which many genes variants combine to determine someone's risk, with each individual one having only a small impact, or those that are due to a combination of genetic and environmental risk factors. These diseases are considered complex or multifactorial. When many genes and environment are involved the landscape changes every time new information becomes available.

Gene variants that had not been considered relevant in the past may be found to have an important impact on disease risk. Some complex diseases may be the result of fewer gene variants exerting a large effect rather than many gene variants exerting small effects. These issues present challenges to companies trying to market tests to accurately predict susceptibility to a given disease.

When several genes are tested at once, information that is unexpected and may not be wanted may surface (Weaver & Pollin, 2012). For example, a patient may discover he or she is at risk for early Alzheimer disease when he or she had agreed to be tested for coronary artery disease risk. Sometimes the same gene variants increase risk of more than one disorder. This underscores the importance of genetic counseling before any genetic testing is performed. Our patients need to make informed decisions about whether or not they wish to be tested.

The most common gene variants that exert a small effect are single nucleotide polymorphisms, commonly called SNPs. Their relationship with disease is often found using Genome-wide Association Studies (GWAS), which examine populations of affected and unaffected people. However, much of the variation in SNPs is restricted to specific populations. People tend to share SNPs with others whose ancestors came from the same geographical region. Using SNPs to predict disease susceptibility is offered by several DTC testing companies. Experts agree that predicting risk using SNP panels has not reached the stage of being clinically useful (Mihaescu et al., 2011).

Type 2 diabetes mellitus as an exemplar

A recently published review reported that there are more than 40 validated locations on the genome that are associated with Type 2 Diabetes Mellitus (Ahlqvist, Ahluwalia, & Groop, 2011). It is unclear how frequently DTC companies update their tests to include new information. The fear, of course, is that consumers will make poorly informed decisions based on unreliable DTC genetic tests. A person could find out that she carries few of the currently known SNPs that predict risk of Type 2 Diabetes Mellitus (TSD) and, because she had not had contact with a genetics professional, she could decide that she did not need to watch her diet and exercise, therefore increasing her risk of actually getting T2D. Perhaps she carries a variant yet to be discovered that dramatically increased her risk unbeknownst to her. This variant could not be tested for in the panel used by the DTC company, so the patient thought that her risk was low.

Advances in genetic testing technology such as affordable sequencing of the whole genome or all the protein-coding areas of the genome may make these kinds of tests more useful in the future, but the consensus is that currently available tests have little clinical validity (Mihaescu et al., 2011).

Recommendations

The major genetics professional organizations have issued statements expressing concern about people making healthcare decisions based on DTC information without consultation from genetics professionals. The concern is balancing the consumer's autonomy and right to access his or her own genetic information with the potential for harm (both physical and psychological) that could arise from inaccurate information and expectations. It is important to remember that genetic information is a bit different from general medical information in that it may provide information about family members as well as the person being tested.

A systematic review of position statements, policies and recommendations on DTC genetic testing from professional organizations and public bodies identified eight documents. These included statements from the American Society of Human Genetics, the European Society of Human Genetics, the International Society of Nurses in Genetics, and the American College of Obstetricians and Gynecologists (Skirton, Goldsmith, Jackson, & O'Connor, 2012).

The authors reported much variation in the statements, but found specific recommendations that could constitute a “code of practice.” These included an agreement on the minimum amount of information that should be provided to consumers before the decision to have genetic testing. They agree that there should be consultation with a health professional knowledgeable about the patient and the test and a list of genetic tests that should not be offered at all without counseling a genetics professional. Finally, health professionals should be provided with sufficient education to allow them to provide needed information about genetic testing to their patients (Skirton et al., 2012). Efforts to provide more information to healthcare providers and consumers are underway.

Genetic testing registry

The National Center for Biotechnology Information (NCBI) of the National Institutes of Health recently launched the Genetic Testing Registry (GTR), a resource for cataloging and providing access to available genetics tests. This is a web-based resource located at http://www.ncbi.nlm.nih.gov/gtr/.

Detailed instructions for its use are available on the site. While the NIH does not independently verify the information about genetic tests submitted to the website, it does provide a central location where laboratories and scientists can submit genetic test information and make it available to providers. In addition, the NCBI asks that people submitting information about genetic tests honor a Code of Conduct by ensuring that the information they provide is accurate and not misleading.

The GTR provides links to clinical genetics resources, such as the GeneTests site mentioned earlier, and facilitates locating a genetic professional in your area. There are also links to consumer resources, such as the Genetics Home Reference (http://ghr.nlm.nih.gov/). This promises to be an excellent clearinghouse for genetic information (NIH Office of Communications, 2012).

While there is little specific information available about how genetic variations affect rehabilitation, we can expect to learn more about this in the future. For example, we know that genetic factors alter the clinical response to neurotrauma. Particular versions of the APOE gene have been associated with poorer long-term outcome to traumatic brain injury (Dardiotis, Grigoriadis, & Hadjigeorgiou, 2012). While clinical genetic testing is not currently being used to guide rehabilitation following neurotrauma, we may see these applications in the not so distant future.

Key Practice Points
  • Clinical genetic tests are available for more than 2,500 diseases.
  • There are biochemical, cytogenetic, and molecular genetic tests.
  • Dose response testing is used to help predict the way a person will respond to a widening selection of drugs.
  • Clinicians must educate themselves about genetic testing options.

Conclusion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Conclusion
  5. References

The landscape for genetic testing is changing constantly. Wise clinicians should take steps to educate themselves about genetic testing options so they can have informed discussions with patients and their families. Excellent resources are available to assist with this venture. It is essential that healthcare professionals take the opportunity to update themselves on genetic information by reviewing the educational materials available on the web from reputable sources such as those mentioned in this article. Furthermore, rehabilitation nurses should become familiar with the ways to access genetics services in their areas and quality resources for patient education.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Conclusion
  5. References
  • Ahlqvist, E., Ahluwalia, T.S., & Groop, L. (2011). Genetics of type 2 diabetes. Clinical Chemistry, 57(2), 241254.
  • American Association of Colleges of Nursing (2008). The Essentials of Baccalaureate Education for Professional Nursing Practice. Retrieved July 30, 2013, from http://www/aacn.nche.edu/Education/pdf/BaccEssentials08.pdf
  • Beery, T.A., & Workman, M.L. (2012). Genetics and Genomics for Nursing and Healthcare Professionals. Philadelphia, Pennsylvania: F.A. Davis.
  • BRCA1 BRCA2. (2009). BRCA1 and BRCA2: Cancer Risk and Genetic Testing. Retrieved March 20, 2012, from http://www.cancer.gov/cancertopics/factsheet/Risk/BRCA
  • Dardiotis, R., Grigoriadis, S., & Hadjigeorgiou, G.M. (2012). Genetic factors influencing outcome from neurotrauma. Current Opinion in Psychiatry, 25, 231238.
  • GeneTests. (2012). GeneTests. Retrieved March 20, 2012, from http://www.ncbi.nlm.nih.gov/sites/GeneTests/
  • Mihaescu, R., Meigs, J., Sijbrands, E., & Janssens, A.C. (2011). Genetic risk profiling for prediction of type 2 diabetes. PLoS Currents, 3, RRN1208.
  • NIH Office of Communications. (2012). Confused by Genetic Tests? NIH's New Online Tool May Help. Bethesda, MD: NIH Office of Communications.
  • Skirton, H., Goldsmith, L., Jackson, L., & O'Connor, A. (2012). Direct to consumer genetic testing: a systematic review of position statements, policies and recommendations. Clinical Genetics, 82: 21018.
  • United Healthcare. (2012). Personalized medicine: Trends and prospects for the new science of genetic testing and molecular diagnostics. United Healthcare Center for Health Reform and Modernization: Minnetonka, Minnesota.
  • Weaver, M., & Pollin, T.I. (2012). Direct-to-consumer genetic testing: what are we talking about? Journal of Genetic Counseling, 21, 361366.