Autism affects about 2% of children in the United States, and about 30% of these children have seizures. Recent large-scale genetic studies have revealed that genetic variants in a sodium channel, called voltage-gated sodium channel Nav1.2, are a leading cause of autism. Overactive sodium channels in the neuron cause seizures. Doctors often treat seizures by giving the patient a medication meant to close the sodium channels, reducing the flow of sodium through axons. For many patients, such treatment works, but in some cases—up to 20 or 30%—the treatment doesn’t work. These children have “loss-of-function” variants in Nav1.2, which is expected to reduce the sodium channel activity as “anti-seizures.” Thus, how the deficiency in sodium channel Nav1.2 leads to seizures is a major mystery in the field that puzzles physicians and scientists.