Vit D Dependent Rickets



- 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



Original Text by Clifford R. Wheeless, III, MD.

Last updated by Data Trace Staff on Tuesday, September 6, 2011 4:03 pm