Introduction and Overview to Genomic Test Reports

Key Points

  • The use of genomic tests (gene panels, exome sequencing, genome sequencing) is increasing in the clinical and research setting.
  • An individual’s genetic code contains millions of differences when compared to the human reference sequence. These differences, referred to here as variants are also sometimes called mutations.
  • Genetic variants may be benign and have no impact or may be pathogenic and causative of disease. When it is unclear whether a variant has an impact it is referred to as a variant of uncertain significance.
  • Genomic tests are often performed to make a diagnosis and explain symptoms. Results related to symptoms are called diagnostic or primary results while results that are unrelated to symptoms are called incidental or secondary results.
  • Results of genomic testing may have medical and personal value to both the individual who underwent testing as well as his relatives.

This guide is intended for healthcare providers faced with understanding and interpreting their patients’ genomic test reports. This guide is not intended to help select a test, but rather to help providers navigate test results.

Genetic Tests vs. Genomic Tests
Genetic testing allows for the identification of changes in chromosomes, genes, or proteins (a gene's encoded product). The results can confirm or rule out a suspected genetic condition or help determine a person’s chance of developing or passing on a genetic disorder.

While genetic testing has been performed for decades, over the past few years there has been a tremendous increase in the number and scope of genetic tests ordered due to improvements in technology and decreases in cost. Genomic tests that explore multiple genes (panels), most genes, and even tests that explore a person’s entire genome, have become a reality. Yet, many healthcare providers have not been trained in how to understand the output of these increasingly common tests.

Next Generation Sequencing (NGS), used in diagnostic testing, generally involves determining the patient’s genetic sequence in millions of short segments, called “reads” (each approximately 100 basepairs in length), assembling the reads into a complete sequence, then determining what genetic variants are present and interpreting what they mean.

Next generation sequencing involves determining an individual’s genetic sequence in millions of short segments which are then assembled into a complete sequence.

Next generation sequencing involves determining an individual’s genetic sequence in millions of short segments which are then assembled into a complete sequence.

NGS is extremely flexible and has been implemented for sequencing only a few genes (e.g., hereditary breast cancer panels) a whole exome (all of the coding regions of DNA) or a whole genome (entire DNA sequence including both coding and noncoding regions).

NGS is now routinely performed in clinical diagnostic laboratories that perform genetic testing and are regulated by CAP and CLIA certifications. However, much is still unknown about when to use which kind of test (gene panels, exome testing, and genome testing), and for what clinical purpose. There are CPT codes for these new NGS tests, but insurance coverage is variable.

For exome or genome sequencing, potentially millions of variants are identified that differ between the patient and the “reference sequence” used for comparison. Most genetic variants have little or no known impact on human health, so the variants must be filtered to identify the few that are medically meaningful. Genomic data from an individual’s parents provides information that can help filter out benign genetic variants and identify de novo variants (variants that are not inherited). Generation of the sequence data, variant calling, and variant interpretation are all critical steps for providing accurate test results.

Genomic testing is often done for an individual patient (singleton) or for a trio (includes patient, mother, and father); however other formats are possible depending on the disease of interest and family structure. Not all laboratories handle the testing and interpretation of parental samples in the same way. In some labs all three individuals are sequenced and interpreted comprehensively at the same time. In other labs the parental samples are only tested after the patient’s sample.

Making sense of genetic variation
Individual genetic variants are classified by the testing laboratory, to indicate whether the laboratory believes a variant to be disease causing (pathogenic) and how certain this assessment is. Laboratories often use a 5-point scale to assign pathogenicity from benign (not disease causing) to pathogenic, with intervening scores of likely benign, variant of uncertain significance, and likely pathogenic. The American College of Medical Genetics and Genomics (ACMG) has published guidelines for laboratories to use in their interpretation and scoring of genetic variation2. However, laboratories will vary in the types of variants they report. Some laboratories may report only pathogenic and likely pathogenic variants while others may report variants of uncertain significance as well. Laboratories typically do not report benign or likely benign findings. Sometimes variants that are associated with causing disease are also called mutations. To reduce confusion, all genetic changes—whether they cause a medical condition or have no impact at all—are now called variants.

Genomic variants are typically classified on a five-point scale to indicate the likelihood that the particular variant is associated with disease.

Genomic variants are typically classified on a five-point scale to indicate the likelihood that the particular variant is associated with disease.

Genomic tests such as exome or genome sequencing can provide different kinds of information. Results that are directly related to explaining a patient’s symptoms or reason for testing are often called primary results, while results that are medically meaningful but unrelated to the reason for testing are often called secondary or incidental results. When using genomic testing to diagnose patient symptoms, examples of secondary results may include genetic risks for future disease, carrier status (carrying a gene for, but not exhibiting, a condition), and pharmacogenomics findings (findings related to differences in how a person may process medications). Often laboratories request information about what kinds of secondary findings a patient would like reported during the test ordering and informed consent process. Laboratories vary in how these choices are categorized and structured.

At this time there is also wide variability among genomic laboratories in the scope and structure of their result reports. During the development of this toolkit, the authors reviewed information from several different labs to help providers make sense of the language they will see in these reports.

Limitations
There are limitations to genomic testing using NGS. A “negative” test report does not exclude the possibility of an underlying genetic disease. There may also be variants of uncertain significance reported that will become better understood over time. Additionally, several types of genetic variants are not robustly detected by NGS methods. The sensitivity of the test is disease specific and should be considered before ordering.

It is highly likely that a genetic variant reported is truly present, particularly if the laboratory uses a second testing method (such as Sanger sequencing) to confirm this. However, it is more difficult to determine the significance of a variant. Laboratories do their best to accurately label genetic variants as pathogenic or likely pathogenic, but a classification may be incorrect. Further, emerging evidence may lead to reclassification. The original report would then have been a false positive.

Should family members be tested?
Genomic test results may provide information about potential genetic variants and risk factors among a patient’s family members. When a genetic variant is identified in an individual, it is important to determine whether relatives are at risk of also having that genetic change and what follow-up testing might be indicated.

What about genetic discrimination?
Many patients may have questions about who will have access to their test results and how that information can be used. Genetic discrimination refers to using a person’s genetic information (test results, family history) against him or her in a harmful way. The Genetic Information Nondiscrimination Act (GINA), a federal law passed in 2008, largely protects against genetic discrimination in the areas of health insurance and employment. However, this legislation does not apply to life, disability, and long-term care insurance. To learn more about GINA, visit http://ginahelp.org/. Individual states may have additional laws that protect against genetic discrimination.

About this toolkit
This toolkit is organized into different sections, based on the different categories of results that may be generated by a genomic test. Each category includes example results and the benefits, limitations, and special considerations associated with each category.

 

Resources

  • ClinGen (http://clinicalgenome.org): a NIH-funded resource that defines the clinical relevance of genes and variants for use in medicine and research.
  • ClinicalTrials.gov (https://clinicaltrials.gov/): a registry and results database of publicly and privately supported clinical studies of human participants conducted around the world.
  • ClinVar (http://www.ncbi.nlm.nih.gov/clinvar/): a public archive of reports about the relationship between specific genetic variants and associated phenotype (symptoms).
  • GeneReviews (http://www.ncbi.nlm.nih.gov/books/NBK1116/): a resource for clinicians that provide clinically relevant and medically actionable information for inherited condition. This resource includes information on diagnostic criteria, management, and information about genetic counseling for patients and their families. There are chapters available about many, but not all, genetic conditions.
  • GINA (http://www.ginahelp.org/): an online resource about genetic discrimination and the Genetic Information Nondiscrimination Act.
  • National Society of Genetic Counselors (http://nsgc.org/): the professional organization for genetic counselors, with patient and provider resources and a searchable tool to “find a genetic counselor” near you.
  • OMIM (http://www.ncbi.nlm.nih.gov/omim): an online resource about human genes and associated phenotype (symptoms).

 

References

  1. Green, R.C., et al. “Clinical Sequencing Exploratory Research Consortium: Accelerating Evidence-Based Practice of Genomic Medicine.” Am J Hum Genet. 2016 Jun 2;98(6):1051-66.
  2. Richards, S. et al. “Standards and Guidelines for Interpretation of Sequence Variants: A joint consensus recommendation of the American College of Medical Genetics and Genomics and Association for Molecular Pathology.” Genetics in Medicine. 2015 17: 405-423.