PIGQ deficiency is a rare genetic disease characterized by intellectual disability, developmental delay, and epilepsy, sometimes with organ anomalies. It is caused by germline mutations in the PIGQ gene which is important for glycosylphosphatidylinositol (GPI) anchor biosynthesis. Cell surface protein can be attached to the cell membrane via GPI anchor, and so mutations in PIGQ lead to the decreased levels of GPI-anchored proteins. GPI anchored proteins play vital roles in numerous biological processes, such as neuronal development. The prevalence of PIGQ deficiency is unknown as it is recently recognized disease, but there have been over 11 patients reported.