ICD-10 Code G40.84 – KCNQ2-related epilepsy (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code G40.84 – KCNQ2-related epilepsy
What it is
G40.84 identifies epilepsy caused by pathogenic variants in the KCNQ2 gene. Use it when documentation specifically links the seizure disorder to KCNQ2-related epilepsy.
Clinical signs
Clinical features vary; refer to documentation. Reported findings may include neonatal or early infantile-onset seizures, recurrent epileptic events, and developmental concerns associated with the genetic diagnosis.
When to use this code
Use this code when the provider documents KCNQ2-related epilepsy, KCNQ2 encephalopathy, or epilepsy due to a confirmed KCNQ2 mutation. It is appropriate when the genetic cause is established in the record, not merely suspected.
If the chart only describes seizures without a documented genetic etiology, code the seizure disorder documented instead. Check documentation for whether the condition is congenital, hereditary, or part of a broader neurodevelopmental diagnosis.
Do not use for
Do not use G40.84 for unspecified epilepsy, isolated febrile seizures, or seizures without a confirmed KCNQ2 association. Do not assign it when the genetic result is absent or unclear.
Coding tip
Verify that the provider links the epilepsy to KCNQ2 in the assessment or genetic report before assigning G40.84.