PLP1 and cask-related x-linked intellectual disability: So far, PLP1 is the only gene known to be involved in XLID, and importantly, this is the first case of microdeletion with syndromic intellectual disability at Xq22.2 without involvement of PLP1. Conspicuously, the transcript levels of GLRA4 were significantly reduced in DGDP084 compared to her healthy mother and this is consistent with the random X-inactivation result suggesting chromosome X with the Xq22.2 microdeletion is not preferentially inactivated.