X-linked hypophosphatemia

X-linked hypophosphatemia is characterized by low levels of phosphate in the blood (hypophosphatemia), which can lead to skeletal abnormalities. Phosphate is a mineral that is essential for the normal development of bones and teeth. Without adequate amounts of phosphate, the bones can weaken or soften, leading to a condition called rickets in growing children or a similar condition called osteomalacia in adults.

The features of X-linked hypophosphatemia vary widely, even among members of the same family. Mildly affected individuals may have hypophosphatemia without other signs and symptoms. More severely affected individuals typically experience slow growth beginning in early childhood, and they may be shorter than their peers. They often develop bone abnormalities that can impair movement and cause pain, such as legs that are abnormally curved (bowed) because the bones are too weak to bear weight. These abnormalities tend to worsen over time.

In adults with X-linked hypophosphatemia, osteomalacia can make the bones more prone to a type of fracture called a stress fracture, which can be painful. Affected adults may also have abnormal calcium deposits that occur near the joints where the ligaments and tendons attach (enthesopathy) and a painful joint disorder called osteoarthritis.

Other signs and symptoms of X-linked hypophosphatemia can include premature fusion of the skull bones (craniosynostosis) and hearing loss. Affected individuals may also have dental abnormalities, which can include pus caused by a bacterial infection (abscess). In rare cases, people with X-linked hypophosphatemia have abnormalities of the spine, which can include a narrowing of the spinal canal that can pinch the upper part of the spinal cord (spinal stenosis) and the formation of fluid-filled cysts (syrinx) within the spinal cord.

With early treatment, people with X-linked hypophosphatemia may have less-severe skeletal signs and symptoms and fewer long-term health issues.