GRIPAP1 and cask-related x-linked intellectual disability: Another strategy, known as Affected Kindred/Cross-Cohort Analysis (Niranjan et al., 2015) has also identified variants in known and novel XLID genes including PLXNA3, GRIPAP1, EphrinB1 and OGT. However, analysis of next-generation data sets has also highlighted a number of XLID genes where truncating variants or previously published “mutations” are observed at a relatively high frequency in normal controls, calling into question whether certain single nucleotide variants (SNVs) are indeed causal (Tarpey et al., 2009; Piton et al., 2013).