Parathyroid disorders

a. Hypoparathyroidism. Associated with chromosome 22q11 abnormalities (see A, 3, a, earlier) or autoimmune syndromes such as autoimmune polyglandular syndrome.

b. Pseudohypoparathyroidism. Disorders of activation of the cellular effects of PTH.

c. Calcium-sensing abnormalities. Occurs when parathyroid gland is abnormally sensitive to serum calcium, causing PTH levels to be low in relation to level of calcium.

d. Hypomagnesemia. Associated with decreased PTH secretion and PTH effect. Vitamin D disorders a. Vitamin D deficiency. Low levels of vitamin D due to dietary insufficiency, lack of sunshine, fat malabsorption, or liver disease.

b. Vitamin D-dependent rickets. Block in 1,25-dihydroxyvitamin D formation (type 1) or abnormal receptor (type 2).

c. Renal failure. Acute or chronic, with inadequate formation of 1,25-dihydroxyvitamin D.

d. Fanconi syndrome. Proximal renal tubular dysfunction with low 1,25-dihydroxyvitamin D formation and renal phosphate wasting.

e. Altered metabolism. Often due to drugs such as phenobarbital, phenytoin, or ketoconazole.

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