P2RX4 and primary progressive multiple sclerosis: For other diseases, the Gly150Arg variant has been associated with reduced bone mineral density and higher risk of osteoporosis [18, 46]; mood disorders [16]; impaired phagocytosis and subsequent aged related macular degeneration (when associated with P2X4R - Tyr315Cys) [47]; and risk of primary progressive multiple sclerosis [48].