Genetic testing in epilepsy has moved far beyond looking for one suspected gene at a time. Depending on the clinical question, testing may now use multigene panels, chromosomal analysis, exome sequencing or genome sequencing.
Why testing has changed
Epilepsy is genetically heterogeneous: many different genes can be involved, and the same gene can produce different epilepsy phenotypes. That makes broad sequencing approaches useful when there is no single obvious candidate.
What exome and genome sequencing add
Exome sequencing analyses the protein-coding regions of genes, while genome sequencing also examines much of the non-coding genome and may identify some variants that exome testing misses. Diagnostic yield varies substantially with age, phenotype, family history, intellectual disability, developmental features and how patients are selected.
A result is not always a simple answer
Testing can identify pathogenic or likely pathogenic variants, but it can also produce variants of uncertain significance or no explanatory finding at all. Interpretation depends on clinical context and may change as scientific knowledge develops.
Why a genetic diagnosis can matter
A confirmed diagnosis may clarify prognosis, end a long diagnostic search, inform recurrence counselling, connect families with condition-specific support, and occasionally influence treatment or eligibility for targeted trials. It does not mean every genetic epilepsy is inherited from a parent; some variants arise de novo.
Who should be offered genetic testing?
Genetic testing is particularly important in developmental and epileptic encephalopathies, early-onset epilepsy, epilepsy with intellectual disability or autism, unusual syndromic features, a strong family history, suspected metabolic or channel disorders and otherwise unexplained drug-resistant epilepsy.
Age alone should not exclude testing. Adults with childhood-onset or unexplained epilepsy can receive a diagnosis decades after seizure onset.
Choosing the test
Testing is no longer simply “a gene test”. Options include targeted single-gene analysis, multigene panels, chromosomal microarray, exome sequencing, genome sequencing, mitochondrial DNA analysis and specialised tests for repeat expansions, methylation abnormalities or structural chromosome changes.
Panels
Epilepsy panels analyse a selected group of genes. They can provide deep coverage and focused interpretation but may become outdated as new disease genes are discovered and may miss diagnoses outside the selected list.
Exome sequencing
Exome sequencing examines most protein-coding regions. Trio sequencing—testing the affected person and both biological parents—can improve interpretation of de novo and inherited variants.
Genome sequencing
Genome sequencing covers coding and non-coding DNA more broadly and can detect some structural, intronic and other variants that exome testing misses. A 2024 paediatric epilepsy study found additional diagnoses after non-diagnostic exome sequencing, including non-coding and difficult-to-detect variants.
Copy-number and structural variation
Deletions and duplications can cause epilepsy. Modern sequencing pipelines may detect many copy-number variants, but chromosomal microarray, karyotyping or other cytogenetic testing remains important in selected situations. Ring chromosome 20 is a clear example where chromosome-level testing can be essential.
Mosaicism
A pathogenic variant may be present in only a proportion of cells. Low-level mosaicism can be missed depending on tissue sampled and sequencing depth. Blood is not always the only informative tissue.
Mitochondrial DNA
Mitochondrial disorders may require specific analysis of mitochondrial DNA, and variant heteroplasmy can differ between blood, urine, muscle and other tissues.
Variants of uncertain significance
A VUS is not a confirmed diagnosis. It means current evidence is insufficient to classify the variant as pathogenic or benign. Clinical decisions should not automatically treat a VUS as disease-causing.
Reanalysis can change the answer
A negative exome or genome result is not necessarily permanent. New gene–disease discoveries, better structural-variant calling and updated classification criteria mean periodic reanalysis can produce diagnoses that were not possible at the original testing date.
Diagnostic yield varies
Yield depends heavily on phenotype and test type. A large 2025 systematic review and meta-analysis covering more than 120,000 people with neurodevelopmental disorders or epilepsy confirmed that sequencing methods provide substantial diagnostic yield, while individual cohorts vary widely according to selection criteria.
Adults benefit too
A 2024 adult epilepsy cohort found meaningful diagnostic yield across exome sequencing, panels and microarray, supporting testing of appropriately selected adults rather than limiting genomic investigation to children.
What a diagnosis can change
A molecular diagnosis can clarify prognosis, identify medication risks or treatment opportunities, avoid unnecessary investigations, guide surveillance for associated conditions, inform reproductive counselling and connect families with condition-specific support and research.
Precision medicine has limits
Finding a gene does not automatically produce a gene-specific treatment. For many genetic epilepsies the greatest immediate value is diagnostic certainty and avoidance of inappropriate therapy; targeted treatments remain available for only a subset of disorders.
Consent and counselling
Testing can reveal unexpected family relationships, secondary findings, uncertain variants and reproductive implications. Pre- and post-test counselling should match the complexity of the test and local health system.
Worldwide access
Genomic sequencing has expanded rapidly but remains unevenly accessible. Cost, laboratory infrastructure, ancestry bias in reference databases and shortages of genetic specialists can all affect diagnostic equity.
The central point
Modern epilepsy genetics is a dynamic diagnostic pathway, not a one-off panel. The right test depends on phenotype, and negative results may warrant broader testing or future reanalysis.
Genetics & Epilepsy →
POLG-Related Epilepsy →
Ring Chromosome 20 Syndrome →
2025 systematic review and meta-analysis — genetic testing in neurodevelopmental disorders and epilepsy
2024 — genome sequencing after non-diagnostic exome sequencing in paediatric epilepsy
Sources
ILAE Genetics Commission — current practice in genetic testing of the epilepsies
Systematic review and meta-analysis of diagnostic yield of genetic testing in epilepsy