PIGP (phosphatidylinositol glycan anchor biosynthesis class P) is a subunit of the glycosylphosphatidylinositol-N-acetylglucosaminyltransferase (GPI-GnT) complex located on the endoplasmic reticulum membrane 1. It catalyzes the transfer of N-acetylglucosamine from UDP-N-acetylglucosamine to phosphatidylinositol, catalyzing the first and essential step of GPI anchor biosynthesis 2. GPI anchors tether over 150 human proteins to the cell surface, which play critical roles in development and neurogenesis 1. PIGP mutations cause inherited GPI deficiencies, a subgroup of congenital disorders of glycosylation 1. Biallelic variants in PIGP result in developmental and epileptic encephalopathy 55, characterized by early-onset refractory seizures, hypotonia, and profound global developmental delay 31. A recent report expanded the phenotype to include multiple congenital anomalies, dysmorphic features, and severity sufficient to cause severe malformations in utero 4. Functional studies demonstrate that PIGP mutations reduce both mRNA levels and GPI-anchored cell surface proteins, which can be rescued by wild-type PIGP expression 1. Additionally, PIGP appears dysregulated in Kawasaki disease, showing diagnostic value for this pediatric vasculitis 5.