ORLANDO — The epilepsy community has yet to come to a consensus on genetic testing. During a session at the annual meeting of the American Epilepsy Society (AES), researchers and clinicians convened to share their insights on genetic testing of adult patients with epilepsy.
Colin Ellis, MD, assistant professor of neurology at the Hospital of the University of Pennsylvania in Philadelphia, shared his clinical experience to explain the importance of genetic testing in adults patients despite access challenges, limited information on certain variants, and physician reticence.
“There’s a false misconception that genetic testing should only apply to children,” Dr. Ellis told the audience. “The earlier the onset of seizures, the more likely you are to find a genetic cause.”
Guidelines Differ
The International League Against Epilepsy Task Force for Clinical Genetic Testing, Development and Epileptic Encephalopathies (DEE) recommends conducting genetic testing in patients who have focal or generalized epilepsies to whom the following circumstances apply: autism or dysmorphism, familial history, or drug-resistant epilepsy.
However, the National Society of Genetic Counselors’ guidelines recommends genetic testing for patients who have any unexplained or idiopathic epilepsies.
Guidelines identify the patients who should get tested regardless of their age.
Personal Experience
Dr. Ellis, who has spent nearly 5 years running tests on patients with epilepsy, recently tested the 300th patient at his clinic. According to him, the yield is higher in focal epilepsy than in general epilepsy — an occurrence that counters what many believe.
“Focal epilepsies are more common than monogenic epilepsies but not intuitive to many people in the industry, despite being stated in the literature,” he said. “The absence of family history shouldn’t preclude you from genetic testing because it’s still possible to have a de novo variant not inherited from either parent.”
Genetic testing can be conducted by interrogating either the exome or the genome. However, cost remains a major barrier to access.
Dr. Ellis made several arguments supporting the use of genetic testing. First, genetic testing allows for a higher diagnostic yield (i.e., 24% versus 19% in panels and 9% in microarrays). Genetic testing provides a more comprehensive overview of a patient’s genetic landscape, and it can enhance the ability to identify certain epileptic conditions, such as those caused by monogenic epilepsy — a condition associated with 926 different genes.
“You’re also less likely to find variants of uncertain significance (VUS),” Dr. Ellis said. “Regardless, you should provide the lab with phenotype information because it will help them help you.”
Variants of Uncertain Significance
The National Human Genome Research Institute defines VUS as a variant found in a patient’s genome for which it remains unclear as to whether a health condition is causing the variant. Oftentimes, such variants have very little information available due to their rarity.
In order to resolve VUS, Dr. Ellis recommended family segregation. “If the VUS appears to be de novo, you should test the parent because if they carry the gene, then it’s probably not the cause,” he said.
Dr. Ellis outlined several steps in resolving VUS.
For starters, clinicians should determine the phenotypic fit and run some ancillary tests. For example, in the case of Glu 1 abnormalities, one should consider conducting a spinal tap to determine whether the patient has cerebral spinal fluid before taking additional action.
In addition, Dr. Ellis recommends defining variant characteristics, as it becomes important in determining whether it is appropriate to take action because the majority of variances are benign.
“The take-home point is that you should not act clinically on a VUS unless you know what you’re doing,” he said. “I also disagree with the belief that VUS are rare — it’s just that they cause so much anxiety because we’re uncomfortable with this kind of testing.”