Recently, we and other groups revealed that gain-of-function mutations in the human ether à go-go voltage-gated potassium channel hEAG1 (K<sub>v</sub>10.1) lead to developmental disorders with associated infantile-onset epilepsy.
Consistent with this result, we find that two mothers of children with TBS, who have epilepsy but are otherwise healthy, are low-level (10% and 27%) mosaic carriers of pathogenic KCNH1 mutations.