What is X-Linked Hypophosphatemia (XLH)?

• X-Linked Hypophosphatemia (XLH) is a heritable bone condition characterized by low blood levels of phosphorus (hypophosphatemia) and rickets in childhood
• A change in a gene called PHEX causes XLH
• Bone cells with the change in PHEX produce excessive amounts of FGF23, an important hormone that regulates phosphorus balance
• Excess FGF23 results in an increase in the elimination of phosphorus through the kidneys, so that the blood phosphorus level becomes reduced
• This hypophosphatemia results in the impaired accumulation of mineral in the bones
• Undermineralized bones are structurally weak and can deform, limiting the capacity for growth and normal development
• Treatment strategies attempt to enhance the phosphorus level by providing oral supplements or with a medicine that blocks FGF23 action at the kidney to reduce losses

The Yale Bone Center (YBC) provides consultative care to adult patients with osteoporosis and genetic disorders of the skeleton, as well as other disorders of bone and mineral metabolism. It is highly regarded locally and nationally. It is directed by Karl Insogna, MD, FACP, Ensign Professor of Medicine, an internationally recognized expert in metabolic bone disorders.

The YBC is composed of three services:

1. A consultative service is staffed by 6 full-time Yale faculty, who provide care in three locations, North Haven, New Haven and Stamford. CT. Two administrators coordinate care and provide logistical support the YBC physicians.
2. The YBC also supports a Bone Densitometry Service that performs bone density studies for both clinical and research purposes and is housed on the 10th floor of the East Pavilion of the Yale New Haven Hospital. All scans are interpreted by a YBC physician and generate in a clinically relevant interpretation of the scan, unlike any other bone densitometry facility.
3. Finally, the YBC supports the Mineral Metabolism Laboratory, which measures blood vitamin D and parathyroid hormone levels for patients seen throughout the Yale healthcare system. It also provides analytical support for a wide range of patient-related clinical research studies conducted by YBC faculty and other members of the Yale academic community.

The Pediatric Metabolic Bone Clinic cares for children with conditions related to bone and mineral metabolism, including XLH and other disturbances in phosphate metabolism, osteogenesis imperfecta, and skeletal dysplasias. The clinic coordinates the services of endocrinology, radiology, physical therapy, orthopaedics, and surgery through its multi-disciplinary approach to patient care.