Category: Calcium/Bone Disorders

A Case of Hypophosphatemic Rickets

Monday, Apr 8
1:00 AM – 2:00 AM

Objective :

We present a case of hypophosphatemic rickets (HR), its differentials, key findings, and treatment.


Methods : N/A


Results : N/A


Discussion :

A 27-year-old African male was evaluated at our clinic. He had dental abnormalities and leg bowing as a child, was given vitamin D, and had surgical correction of fractures. He moved to the USA, was found to have hypophosphatemia, and has been taking phosphate and vitamin D since. Labs include: phosphorus 1.6 mg/dL, calcium 9.0 mg/dL, PTH 56 pg/mL, alkaline phosphatase (ALP) 160 mg/dL, 24-hr urine phosphate 1200 mg, 25-hydroxyvitamin D 13 ng/mL, 1,25-dihydroxyvitamin D 56 pg/mL. Radiographs showed diffuse bony demineralization, bowing of femurs, insufficiency fractures and pseudofractures in the lower extremities. On physical exam, he has a short stature, frontal bossing, bowing of both lower extremities, and a slow, antalgic gait. His phosphorus level improved with replacement but his dose had to be decreased beause of gastrointestinal side effects. He has bilateral hip and lower extremity pain. The following additional tests are pending: FGF23, 24-hr urine calcium, skull x-ray, and technetium pertechnetate bone scan. Genetic testing will follow.
X-linked hypophosphatemia (XLH) is the most common cause of HR. The clinical and biochemical presentation of XLH, autosomal dominant HR, and autosomal recessive HR are similar but phenotypes may vary. Affected persons have skeletal deformities, dental defects, hypophosphatemia, renal phosphate wasting, low or normal 1,25-dihydroxyvitamin D, and elevated serum ALP and FGF23. Fanconi syndrome is caused by defects in the proximal tubule resulting in renal wasting of phosphorus. Tumor induced osteomalacia is caused by tumors secreting FGF23. Mutations of the sodium phosphate co-transporter result in hypophosphatemia with a compensatory decrease in FGF23, leading to increased 1,25-dihydroxyvitamin D and intestinal calcium absorption. This results in hypercalcemia, hypercalciuria, and nephrocalcinosis.  Hereditary hypophosphatemic rickets with hypercalciuria is described in the Bedouin people who are historically known to inhabit North Africa. Nutritional deficiency and mutations affecting 1α-hydroxylase, vitamin D receptor, and vitamin D metabolism may also cause hypophosphatemia with low FGF23. Early treatment is often difficult due to delay in diagnosis. Conventional therapy includes phosphate and vitamin D supplementation. Burosumab, an FGF23 blocking antibody, shows promise in recent clinical trials.


Conclusion :

There are different causes of hypophosphatemic rickets. Although conventional therapy is the same, appropriate diagnosis should be made especially in the advent of new treatment.

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Marie Angelica Landicho

Endocrinology Fellow
University of Florida College of Medicine - Jacksonville
Jacksonville, Florida

Ateneo de Manila University (Quezon City, Philippines), B. S., Completion in 2007
University of Santo Tomas (Manila, Philippines), M. D., Completion in 2011
2011-2012 Postgraduate Internship Training, University of Santo Tomas Hospital (Manila, Philippines)
2014-2017 Internal Medicine Residency, Monmouth Medical Center (Long Branch, New Jersey)
2017-present Endocrinology Fellowship, University of Florida College of Medicine – Jacksonville (Jacksonville, Florida)

Kent Wehmeier

Program Director, Endocrinology Fellowship
University of Florida College of Medicine - Jacksonville
Jacksonville, Florida

Medical Education: University of Missouri, Columbia School of Medicine, Columbia, MO, USA
Residency: Internal Medicine, Washington University, St. Louis, MO, USA
Fellowship: Endocrinology, Diabetes and Metabolism, St Louis University School of Medicine, St. Louis, MO, USA

Marie Angelica Landicho

Endocrinology Fellow
University of Florida College of Medicine - Jacksonville
Jacksonville, Florida

Ateneo de Manila University (Quezon City, Philippines), B. S., Completion in 2007
University of Santo Tomas (Manila, Philippines), M. D., Completion in 2011
2011-2012 Postgraduate Internship Training, University of Santo Tomas Hospital (Manila, Philippines)
2014-2017 Internal Medicine Residency, Monmouth Medical Center (Long Branch, New Jersey)
2017-present Endocrinology Fellowship, University of Florida College of Medicine – Jacksonville (Jacksonville, Florida)