PRRT2 and Global developmental delay: [7, 8] In addition, a small number of patients have been identified who carry biallelic mutations in PRRT2, resulting in a more severe phenotype that includes intellectual disability, developmental delay, ataxia, and paroxysmal dyskinesias.[9] PRRT2 mutations were found primarily to lead to a loss of function through nonsense-mediated decay, pointing to a haploinsufficiency mechanism.