X-Linked Hypophosphatemia (XLH)

Symptoms vary between people, and the disease occurs with various degrees of severity. Low concentrations of phosphate in the bloodstream and inhibited activation of vitamin D in the kidneys lead to a lack of mineralization of the skeleton and teeth, making the skeleton soft. This causes misalignments in the legs, like bow-leggedness (genu varum) or knock knees (genu valgum), and often also some twisting, meaning that the feet or the knees point in or outwards. Length growth in childhood is impaired, and the final length is, on average, around 15 cm shorter than expected. 
 
The misalignments vary from mild with problem-free patients to more severe ones, which can lead to abnormal and waddling gait, cracks and fractures of the femur and lower leg, pain from bones and muscle attachments, and early-onset osteoarthritis.   
 
Tooth root infections and tooth loss are common, as the teeth are also affected by the lack of phosphate. Many also have hearing loss due to the bones in the head being affected by the disease. These bones can end up being thickened and cause cramped conditions in the ear canals. Head shape can be asymmetrical or deviant as the growth plates are sometimes closed too early. 

For patients with a family history of the disease, the diagnosis is often made with genetic testing as early as 3–6 months of age. In cases where it is caused by a new mutation, it is more common to discover the condition when children start to walk since height growth slows down and the legs become bent. 

The treatment of phosphate deficiency is handled by endocrinologists and monitored with blood tests. The treatment of the skeleton and its misalignments are dealt with by orthopedists who, among other things, use so-called HKA X-ray and computed tomography for mapping. 
 
XLH is an uncommon disease that can affect many of the body's organ systems and should be treated in hospitals with experience in treating the disease and with access to multidisciplinary teams. 

Children are referred to the Dysplasia team at Karolinska University Hospital, which follows the patient until they are fully grown. After age 18, the patient is assigned to our Deformity team at the adult orthopedist if problems with the musculoskeletal system persist.  
 
Treating misalignments or short stature is an individual decision, and we assess and treat each patient based on their needs and symptoms. The goal of treatment is always to improve the patient's function or prevent future problems. 
 
During a patient’s growth period, bow-leggedness can be remedied or reduced by temporarily slowing the development on the outside of the knee by putting a small so-called eight-plate over the growth plate. Grown-ups with a misalignment that causes problems or can lead to osteoarthritis and, therefore, need correction require a slightly more extensive procedure, a so-called osteotomy (splitting the bone) that re-angles, de-rotates, and possibly lengthens the leg.  
 
Far from everyone chooses to undergo leg lengthening, one must carefully consider the procedure's benefit against the risks always associated with the surgery. 

At Karolinska University Hospital, we have extensive experience correcting misalignments in XLH. We always recommend correcting severe misalignments that can otherwise lead to osteoarthritis and impair walking ability. In the case of short stature, when the patient experiences a problem in everyday life, we can also offer an extension of arms or legs to achieve an increased level of function and quality of life.