Loss of PIGO function through bi‐allelic pathogenic variants in the PIGO gene leads to a severe inborn error of metabolism first reported in 20124 and characterized in most patients by severe global developmental delay, focal neurological disease (such as seizures or movement disorders), and congenital malformations of which the most common is Hirschsprung disease. The gene discussed is PIGO; the disease is Hirschsprung disease.