Beyond paroxysmal neurological disorders, there is preliminary evidence that heterozygous PRRT2 mutations might also cause intellectual disability and/or developmental delay (26, 27, 38), a suggestion supported by their invariable presence in cases with 16p11.2 deletions (39–41) and homozygous PRRT2 mutations (27, 42–44). The gene discussed is PRRT2; the disease is Global developmental delay.