- See:
Rickets:
- Type-I vitamin-D-dependent rickets or osteomalacia:
- failure of conversion of 25-hydroxyvit D to
1,25-dihydroxyvit D is the cause of this disorder;
- defect is not clearly understood but may be a deficiency or an abnormality of the renal 1-hydroxyvitamin-
D-25-hydrolase, believed necessary for the conversion of 1-hydroxyvitamin D to 1,25-Vit D;
- this is an autosomal recessive disorder;
- disorder is considered to be a pseudodeficiency state in which patient does not respond to even large doses of
orally administered vitamin D, despite a rise in the amount of 25-hydroxyvitamin D generated by the liver;
- patients may manifest
hypocalcemia,
hypophosphatemia, and increased
alkaline phosphatase;
- in some cases the defect can be overcome with large doses of vitamin D, but more importantly it can be
completely eliminated by physiological doses of
1,25-dihydroxyvitamin D;
- Type-II vitamin-D-dependent rickets or osteomalacia:
- this is believed to represent an end-organ insensitivity to autogenous 1,25-dihydroxyvitamin D;
- pathogenesis is obscure but the cause appears to be a genetic error that results in the failure
of the gut (and other) cells to recognize autogenous 1,25-dihydroxyvitamin D;
- this is an autosomal recessive disorder;
- patients become rachitic despite normal or high serum concentrations of 25-hydroxyvitamin D &
1,25-dihydroxyvitamin D & remain rachitic despite high doses of vitamin D or calcitriol in diet;
- this syndrome may share similarities to
hypophosphatemic rickets with alopecia in which
the nuclear receptor for 1,25-dihydroxyvitamin D in the gut cell is genetically altered;
- patients may manifest
hypocalcemia;
- these patients may respond to exogenously administered synthetic
1,25-dihydroxyvit D but
may need additional calcium administered orally or by infusion for the control of symptoms;
