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In 1992, a 33-year-old Lebanese woman immigrated to Canada and went to see a doctor. She was curved and her mobility was limited in the lower back, neck, shoulders and hips. Her doctor, Raymond Lewkonia, of the University of Calgary, diagnosed her with ankylosing spondylitis, a condition that causes vertebral fusion of the spine.
Then, about eight years later, the woman had a series of broken ribs, feet, left arm and right hip. Her doctor had her take vitamin D supplements, but they had no effect: laboratory tests revealed she did not have vitamin D circulating in her blood.
It seemed impossible. Some vitamin D, after all, is thought to be essential for Maintaining bone health and taking supplements after an injury or fracture is commonly used to speed up the healing process. Why does this vital substance not exist in the woman's system?
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Dr. Patrick Ferreira, a medical geneticist who examined the case, suspected that a protein-binding associated with vitamin D to enter and around the body – or lack thereof – might have something to do with this medical mystery. But losing the ability to carry vitamin D would be deadly for humans, according to what doctors usually know.
Dr. Ferreira set out to test his hypothesis, but had difficulty confirming that the vitamin D binding protein was indeed absent from the woman's system. He and others sent blood samples to labs in Europe and Vancouver, but these tests – which may not be reliable – came back claiming that binding protein levels were normal. When Dr. Ferreira retired, he forwarded the patient's file to his colleague, Dr. Julien Marcadier, a clinical geneticist at the Research Institute of Alberta Children's Hospital, who is currently the lead author of a case report published last month in the New England Journal of Medicine.
Fortunately for Dr. Marcadier, researchers at the University of Washington in Seattle had come up with a more sensitive method of protein detection.
Dr. Andrew Hoofnagle and his colleagues agreed to examine the blood sample and found that there was no vitamin D in his blood, nor vitamin D binding protein .
"When you think about the biology of vitamin D," said Dr. Hoofnagle, "it should not work, that person should not be alive.
Martin Hewison, a molecular endocrinologist at the University of Birmingham in England, who did not participate in the study, says this case is the first of its kind.
How could this woman have lived nearly six decades without a substance deemed essential to human life?
While vitamin D binding protein sequesters vitamin D in the body, these are the unbound molecules of vitamin D that are ultimately important for bone growth.
"The amount of vitamin D needed can vary from one organ to another," said Dr. JoAnn Manson, Endocrinologist and Principal Investigator of the Vitamin D and Omega-3 Trials at Boston's Brigham and Women's Hospital. . In this case, the amount of free vitamin D that this woman has received from her diet or sun exposure may have been sufficient to develop her bones and keep them alive.
And it remains to be determined how much vitamin D our body needs, although some Recent research suggests that the dose of vitamin D may be of little importance for bone mineral density, fractures or falls for old people.
"I do not think it argues for the need for less vitamin D, but simply the body's ability to adapt to a limited vitamin D binding protein," said Dr. Ellen Fung, Director from the Bond Density Clinic at the Oakland Children's Hospital Research Institute in California, "although she eventually caught up with her."
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