About x-linked hypophosphatemia (xlh)

What is x-linked hypophosphatemia (xlh)?

Familial hypophosphatemia is a rare inherited disorder characterized by impaired transport of phosphate and often altered vitamin-D metabolism in the kidneys. In addition, phosphate may not be well-absorbed in the intestines. The hypophosphatemia resulting from these impairments can lead to a skeletal defect called osteomalacia, which can be considered a softening of bones. Familial hypophosphatemia also results in rickets, a childhood bone disease with characteristic bow deformities of the legs, as well as growth plate abnormalities and progressive softening of the bone as occurs in osteomalacia. In adults, the growth plate is not present so that osteomalacia is the evident bone problem. In children, growth rates may be slower than normal, frequently resulting in short stature. Familial hypophosphatemia is most often inherited as an X-linked trait. However, autosomal dominant and recessive forms of familial hypophosphatemia occur.

What are the symptoms for x-linked hypophosphatemia (xlh)?

Many people with mild hypophosphatemia don’t have symptoms. Symptoms may not appear until your phosphate levels drop very low.

When symptoms do occur, they can include:

  • muscle weakness
  • fatigue
  • bone pain
  • bone fractures
  • appetite loss
  • irritability
  • numbness
  • confusion
  • slowed growth and shorter than normal height in children
  • tooth decay or late baby teeth (in familial hypophosphatemia)

What are the causes for x-linked hypophosphatemia (xlh)?

Because phosphate is found in many foods, it’s rare to have a deficiency — unless you’re malnourished. Certain medical conditions can cause hypophosphatemia by:

  • decreasing the amount of phosphate your intestines absorb
  • increasing the amount of phosphate your kidneys remove into your urine
  • moving phosphate from inside the cells to the area outside the cells

Causes of hypophosphatemia include:

  • severe malnutrition, such as from anorexia or starvation
  • alcoholism
  • severe burns
  • a diabetes complication called diabetic ketoacidosis
  • the kidney disorder, Fanconi syndrome
  • an excess of parathyroid hormone (hyperparathyroidism)
  • chronic diarrhea
  • vitamin D deficiency (in children)
  • inherited conditions such as X-linked familial hypophosphatemia (XLH) or hereditary hypophosphatemic rickets with hypercalciuria (HHRH)

Low phosphate levels may also be due to long term or excess use of certain drugs, such as:

  • diuretics
  • antacids that bind to phosphate
  • theophylline, bronchodilators, and other asthma medicines
  • corticosteroids
  • mannitol (Osmitrol)
  • hormones such as insulin, glucagon, and androgens
  • nutrients such as glucose, fructose, glycerol, lactate, and amino acids
  • bisphosphonates
  • acyclovir (Zovirax)
  • acetaminophen (Tylenol)

Familial hypophosphatemia is caused by gene changes (mutations) that are passed down from parents to their children. These gene changes cause the kidneys to remove more phosphate than usual from the blood into the urine.

What are the treatments for x-linked hypophosphatemia (xlh)?

Early diagnosis and treatment can help improve your outcome. Treatment can help curb symptoms and may encourage positive growth and development.

The main goal of treatment is to get more phosphate into the blood. Traditionally, this has been accomplished through daily phosphate supplements. Your doctor may also prescribe or recommend vitamin D supplements.

A newer medication, burosumab (Crysvita), works by targeting the excess hormone that affects phosphate levels, FGF23. This medication is an injection administered by a doctor every few weeks.

In some cases, your doctor may recommend surgery to help correct bone deformities.

Maintain your oral health by brushing your teeth and keeping them as clean as possible. Regular dentist visits can help with this as well.

What are the risk factors for x-linked hypophosphatemia (xlh)?

You’re more likely to get hypophosphatemia if you:

  • have a parent or other close family member with the condition
  • have the blood infection, sepsis
  • have hyperparathyroidism
  • are severely malnourished because of starvation or anorexia
  • are an alcoholic
  • take medications such as steroids, diuretics, or antacids in excess or for long periods of time

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