Complex sentence: It is associated with a mutation in the PHEX gene sequence (Xp.22) and subsequent altered (or missing) activity of the PHEX protein, which inactivates hormone-like substances (phosphatonins) that promote phosphate excretion and impair bone mineralization.
Split into simpler sentences: It is associated with a mutation in the PHEX gene sequence (Xp.22) and subsequent inactivity of the PHEX protein. The mutation results in altered (or missing) activity of the PHEX protein, which inactivates hormone-like substances (phosphatonins) that promote phosphate excretion and impairs bone mineralization.