Vitamin D-dependent rickets types I and II. Diagnosis and response to therapy

The diagnostic value of measuring serum vitamin D metabolites is demonstrated in the present study in which two patients with vitamin D-dependent rickets (VDDR) Types I and II are reported. The patient with sporadic VDDR Type I was severely disabled and unable to walk. Her serum 1,25(OH)2D level was low (32 pg/ml, normal 30 to 60) and she responded dramatically to 1 microgram of 1 alpha-hydroxyvitamin D3 daily. The VDDR Type II patient had an autosomal recessive inheritance and total alopecia. His serum 1,25(OH)2D level was greater than 500 pg/ml, compatible with end-organ refractoriness to 1,25(OH)2D. He did not respond to daily doses of 1 microgram 1 alpha-hydroxyvitamin D3. These cases demonstrate the striking difference in 1,25(OH)2D levels and therapeutic response to 1,25(OH)2D in these two conditions.