PIGQ encodes a component of the glycosylphosphatidylinositol-N-acetylglucosaminyltransferase (GPI-GnT) complex, which catalyzes the initial step of GPI anchor biosynthesis by transferring N-acetylglucosamine to phosphatidylinositol in the endoplasmic reticulum 1. This modification is essential for anchoring over 150 cell surface proteins to cell membranes and facilitating their trafficking to lipid rafts 1. PIGQ functions cooperatively with ARV1, which enhances GPI-GnT activity by facilitating efficient phosphatidylinositol recruitment 2. Pathogenic biallelic PIGQ variants cause multiple congenital anomalies-hypotonia-seizures syndrome 4 (MCAHS4), characterized by early infantile epileptic encephalopathy, axial hypotonia, developmental delay, and congenital anomalies 3. Affected individuals display reduced GPI-anchored protein expression on leukocytes, confirmed by flow cytometry, which can be restored by wildtype PIGQ transfection 3. Clinical presentations vary widely, including seizure onset between 2.5-7 months, gastrointestinal complications (including midgut volvulus), cardiac arrhythmias, and cerebellar atrophy 31. Pathogenic variants are associated with increased mortality and life-threatening rhabdomyolysis during febrile infections 4. The phenotypic spectrum also includes nonprogressive congenital ataxia and intellectual disability 1.