PGAP1 and Cognitive impairment: Other glycosylphosphatidylinositol (GPI) synthesis genes are associated with severe cognitive impairment and seizures: PIGM mutations cause glycosylphosphatidylinositol deficiency (MIM 610293), those in PIGL cause CHIME syndrome (MIM 280000), PIGY mutations cause hyperphosphatasia with mental retardation syndrome 6 (MIM 616809), whereas those in post-GPI attachment to proteins 1 (PGAP1) cause mental retardation 42 (MIM 615802) (Table 2).