Epilepsy is a common chronic neurological disorder characterized by recurring spontaneous seizures with cognitive and psychosocial comorbidities. Genetic factors play a crucial role in the cause of epilepsy. We report two patients with epilepsy carrying the variants in KCNJ3 gene, which encodes a potassium channel. For the patients, the seizures occurred at a young age and were under control after combined treatment. Electrophysiological analysis was performed and revealed that the KCNJ3 variants significantly compromised the current activities. Our findings suggest that the KCNJ3 variants are associated with early-onset epilepsy. Genetic testing of KCNJ3 in patients with epilepsy may serve as a strategy for precision medicine. (By Dr Lili Long, https://jmg.bmj.com/content/61/4/319 )