Mutations in the PIGV, PIGO, PIGL, PIGY, PGAP2, PGAP3, and PIGW genes have recently been reported to cause hyperphosphatasia accompanied by mental retardation syndrome (HPMRS); the latter is an autosomal-recessive neurological disorder typically characterised by recurrent seizures, intellectual disability, and distinct facial features. The gene discussed is PIGO; the disease is Elevated circulating alkaline phosphatase concentration.