CASK and Epileptic encephalopathy: Our detailed analysis of the impact of mutations on CASK pre-mRNA splicing and protein expression indicates a genotype-phenotype correlation: inactivating CASK germline mutations are associated with the most severe phenotype (MICPCH with severe epileptic encephalopathy), while in the mosaic state these mutations result in an attenuated phenotype (MICPCH) that can also be caused by partly penetrant CASK mutations.