XLH, or X-linked hypophosphatemia, is a genetic disease that affects the health of bones in both children and adults

XLH in children
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.
Treatment goals in children with XLH may include:
- Increasing and sustaining blood phosphorus levels within the normal range
- Healing rickets and correcting leg deformities
- Increasing height
When discussing XLH with your child’s doctor:
Ask about the impact of having low phosphorus levels, including the long-term effects of rickets and delayed growth and how that may affect your child.
Learn more about starting CRYSVITA to help your conversation with your doctor

XLH patient, Cera
XLH in children manifests as rickets and osteomalacia.
XLH in adults
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.
Treatment goals in adults with XLH may include:
- Increasing and sustaining blood phosphorus levels within the normal range
- Healing active fractures/pseudofractures and osteomalacia
- Improving XLH-related joint stiffness
When discussing XLH treatment options with your doctor:
Be open about all symptoms you are currently experiencing. Ask for a skeletal evaluation to check for possible fractures. Phosphorus is important for healthy bones even when you’re an adult.
Learn more about starting CRYSVITA to help inform your conversation with your doctor

XLH patient, Aly
XLH in adults manifests as osteomalacia, which can lead to fractures and pseudofractures.