Inclusion Criteria:

• 1. Age between 6 and 21 years (inclusive) at time of consent.
• 2. Confirmed CNKSR2 mutation, as demonstrated by genetic testing and confirmed by the investigators.
• 3. Confirmed intellectual disability or developmental delays, as defined by the American Academy of Pediatrics (Moeschler, J, et al. 2014).

Exclusion Criteria:

• 1. Known pathogenic or clinically suspected mutation in a seizure-associated gene besides CNKSR2.
• 2. Confirmed mutation in a gene besides CNKSR2 that is known to increase the severity of the seizure phenotype.
• 3. Known central nervous system structural abnormality confirmed by imaging scan of the brain that is not consistent with the clinical phenotype of CNKSR2 EAS / ID.