Interestingly, Cho et al. recently reported that some XLID patients have mutations in the SIZN1/ZCCHC12 (PNMA10) gene that locates approximately 6 Mb downstream of SIRH11/ZCCHC16 and indicated this gene to be a good candidate for XLID [43]. This evidence concerns the gene RTL4 and cask-related x-linked intellectual disability.