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©2013 UpToDate ® Print Email Diagnostic approach to calcipenic (hypocalcemic) rickets Calcipenic rickets is sometimes termed "hypocalcemic rickets," but this term is not completely accurate because serum calcium is not always low in this disorder. Calcipenic rickets is most commonly caused by vitamin D deficiency. Calcipenic rickets also may be caused by a mixed deficiency of vitamin D and calcium. * Vitamin D dependent rickets type I (VDDR-I), also called pseudo-vitamin D deficiency, is caused by defective conversion of 25-hydroxyvitamin D to 1,25 dihydroxyvitamin D. • Hereditary vitamin D resistant rickets (HVDRR) has also been called vitamin D dependent rickets type II. It is a rare disorder characterized by end-organ resistance to vitamin D, usually caused by a defect in the vitamin D receptor.