Epilepsy is a feature in 4H and human post-mortem studies on temporal lobe epilepsy have identified increased levels of GAD67.56 In models of epilepsy, upon neuronal excitotoxicity and increased glutamate release, GAD65/67 is upregulated as compensatory mechanism to convert excess of glutamate into GABA.57 If the increase in GAD65/67 immunoreactivity is indeed a secondary effect in 4H this would explain why there is no change in the number of GABAergic cells in the iPSC-derived cultures. Here, GAD1 is linked to epilepsy.