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Calcium, vitamin D, and bone disorders 

Calcium, vitamin D, and bone disorders
Chapter:
Calcium, vitamin D, and bone disorders
Author(s):

Gary Butler

and Jeremy Kirk

DOI:
10.1093/med/9780198786337.003.0010
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date: 31 July 2021

Calcium metabolism is complex and dependent upon parathyroid hormone (PTH), calcitonin, and vitamin D3.

Bone mineralization is dependent on normal health, diet growth, and puberty.

Osteoporosis or osteopenia is a loss of total bone content, due to:

decreased bone formation

increased bone resorption.

Osteomalacia is a defect in bone mineralization.

Osteogenesis imperfecta is the most common cause of primary osteoporosis (although rare).

Bisphosphonates can be used to reduce symptoms.

Hypocalcaemia (<2.2 mmol/L) can be caused by:

primary hypoparathyroidism

PTH resistance syndromes

hypomagnesaemia

vitamin D deficiency

activating mutations of calcium-sensing receptor gene (CASR)

autoimmune (may occur as part of polyglandular syndrome)

metabolic disease.

Albright’s hereditary osteodystrophy (AHO):

is a family of PTH resistance syndromes caused by abnormalities in function of the GS-α‎ part of the G protein-coupled PTH receptor (GNAS1 gene).

Treatment is with 1α‎-hydroxyvitamin D3 (alfacalcidol). Oral calcium supplements may be needed.

Hypercalcaemia is rare in infancy and childhood; calcium >2.65 mmol/L usually detected by chance. Caused by:

neonatal primary hyperparathyroidism: homozygous inactivating mutations of the CASR gene

Williams syndrome, with mild hypercalcaemia is a feature in 20%

vitamin D excess.

Rickets can present with:

symptoms and signs of hypocalcaemia

muscle weakness

metaphyseal flaring

bowed legs

rickety rosary.

Treatment is with vitamin D3 or D2.

Other genetic forms of rickets are rare.

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