XLH affects the body

Phosphorus

Children with XLH don’t have enough phosphorus in their bodies. Phosphorus is a mineral that is important to the health and function of bones, muscles, and teeth. Having too little phosphorus—or hypophosphatemia—can cause bones to be weak, leading to childhood conditions like rickets.

Rickets

Rickets is a major symptom of XLH and usually becomes apparent around the time a child begins standing or walking (about 1 to 2 years of age). Rickets can cause pain, delayed growth, and bone deformities in the legs. As a result, children with XLH may face physical challenges.

Impaired growth

Low levels of phosphorus can affect bone growth, so children with XLH tend to be short for their age.

Phosphorus

Adults with XLH continue to have low levels of phosphorus in their bodies. Phosphorus is a mineral that is important for the health and function of bones, muscles, and teeth—not just during childhood when the body is growing, but also in adulthood. Not having enough phosphorus can cause osteomalacia, a condition often described as the weakening of bones. Osteomalacia continues throughout adulthood.

Osteomalacia and fractures

Osteomalacia weakens bones, making them prone to break easily. Normally, minerals like phosphorus are continuously added to bones. This process, called “mineralization,” helps keep bones hard. People who have XLH don’t have enough phosphorus in their bodies for bones to properly mineralize, which causes some parts of bones to be more likely to fracture (break). Bones in the feet, legs, and hips are vulnerable to fractures and pseudofractures, which can be painful and limit a person’s ability to move.

Joint stiffness

Adults with XLH commonly experience physical symptoms resulting from osteomalacia and deformed bones and joints. These can include joint pain and stiffness, which may restrict range of motion.