To determine whether altered genome-wide DNA methylation patterns are associated with KDM5C mutations, we performed genome-wide DNA methylation analyses using the Illumina Infinium HumanMethylation27 BeadChip array containing 27,578 CpG sites and covering >14,000 genes in DNA from blood samples of XLID patients and controls. Here, KDM5C is linked to cask-related x-linked intellectual disability.