SLC6A8 and cask-related x-linked intellectual disability: Seven families could be re-contacted and variant segregation analysis of the respective eight candidate variants was performed: HUWE1, IQSEC2, MAOA, MED12, PHF8, SLC6A8, SLC9A6, and SYN1. Our results show the utility of targeted next-generation sequencing in unravelling the genetic origin of XLID, especially in retrospective cases.