PIGO and Elevated circulating alkaline phosphatase concentration: For instance, Hirschsprung's disease (HD), which is a relatively common feature in cases with ‘hyperphosphatasia with mental retardation syndrome' (HPMRS1) due to PIGV mutations (OMIM #239300),43 has only been reported in one individual with PIGO mutations (HPMRS2; OMIM #614749).44 The HD diagnosis for 263039 therefore provides additional evidence that intestinal disorders can be observed across different genetic HPMRS subtypes.