The epileptic encephalopathies (EE) are a devastating group of epilepsies where frequent seizures result in neurological damage. Although international studies show 1 in 2000 infants develop EE by 18 months, there is little known about the number of children that develop these severe epilepsies after that age and no New Zealand data. The EEs are considered to be genetic disorders, however the causative gene is unknown in half of affected children. Genetic diagnosis is important as it leads to personalised care, accurate genetic counselling, and in some cases emerging therapeutic options. This study aims to discover how many children develop EE prior to their 16th birthday, and the cause of their epilepsy. The study will also identify a genetic cause for children who do not have a genetic diagnosis by using genetic strategies to consolidate known and suspected EE genes as well as make new genetic discoveries.