PIGO (phosphatidylinositol glycan anchor biosynthesis class O) encodes the catalytic subunit of ethanolamine phosphate transferase 3 complex, which catalyzes the tenth and final synthetic step of glycosylphosphatidylinositol (GPI) anchor biosynthesis 1. Specifically, PIGO transfers an ethanolamine phosphate group from phosphatidylethanolamine to the 6-OH position of the third alpha-1,2-linked mannose of the GPI anchor precursor, generating the mature H7 intermediate 2. This modification is essential for proper GPI-anchor attachment to cell surface proteins critical for neuronal and embryonic development 3. PIGO deficiency constitutes a congenital disorder of glycosylation characterized by severe neurological manifestations including intractable epilepsy, severe developmental delay, hypotonia, and ataxia 43. Biochemically, PIGO mutations result in decreased GPI-anchored proteins on blood cells and elevated serum alkaline phosphatase (hyperphosphatasia) 4. Additional features reported include palmoplantar keratoderma and platelet dysfunction 5. Clinically, PIGO-deficient patients present with infantile epileptic encephalopathy and profound developmental delay 3. The condition follows autosomal recessive inheritance, with phenotypic variability ranging from mild to severe presentations 5. PIGO is recognized as a significant genetic cause of hyperphosphatasia with impaired intellectual development syndrome type 2, expanding the spectrum of GPI-anchor deficiency disorders.