Investigators will try to characterize the safety profile of ataluren in patients with CDKL5 or Dravet syndrome resulting from a nonsense mutation and evaluate changes in convulsive and/or drop seizure frequency from Baseline following ataluren treatment in patients with CDKL5 or Dravet syndrome resulting from a nonsense mutation. Investigators will measure changes in minor seizure types (absence, myoclonic, complex partial/focal dyscognitive) following ataluren treatment in patients with CDKL5 or Dravet syndrome resulting from a nonsense mutation and changes from Baseline in cognitive, motor, and behavioral function as well as QOL following ataluren treatment in patients with CDKL5 or Dravet syndrome resulting from a nonsense mutation.