title: A case report of defective endogenous vitamin D: a new clinical entity.
abstract: OBJECTIVE
  To report a case of defective endogenous vitamin D with excellent response to low dose calcitriol replacement therapy.
  
  
  METHODS
  We describe the patient's clinical presentation, biochemical workup, and clinical course.
  
  
  RESULTS
  The patient initially presented with severe symptomatic hypocalcemia and was diagnosed with pseudohypoparathyroidism type 1b at an outside hospital and started on calcitriol 2.25 mcg twice daily with good response but calcitriol was stopped later for cost concerns which led to recurrence of symptoms, worsening hypocalcemia and increased parathormone levels. On review of her case it was noted that her 1,25 dihydroxy: vitamin D level was within normal limits even before she started taking calcitriol, which is not consistent with pseudohypoparathyroidism type 1b. Restarting low dose calcitriol (0.25 mcg twice daily) improved the patient's calcium level to 10.1 mg/dl and decreased the parathormone level to 17 pg/ml and symptoms resolved. Conditions associated with low serum calcium and high parathormone include pseudohypoparathyroidism, vitamin D deficiency and vitamin D resistance. This patient does not fit into any of the known entities causing hypocalcemia and elevated parathormone.
  
  
  CONCLUSIONS
  We hypothesize that this patient had an inadequate number of vitamin D receptors that was corrected by exogenous administration of vitamin D.
authors.affiliation: Department of Medicine, University of Arizona, College of Medicine, Tucson, Arizona, USA.
authors.forename: Aswani
authors.initials: A
authors.lastname: Alavala
authors.affiliation: Department of Medicine, University of Arizona, College of Medicine, Tucson, Arizona, USA.
authors.forename: Hussein
authors.initials: H
authors.lastname: Yassine
authors.affiliation: Department of Medicine, University of Arizona, College of Medicine, Tucson, Arizona, USA.
authors.forename: Harold M
authors.initials: HM
authors.lastname: Szerlip
keywords: 1,25 vitamin D; defective endogenous vitamin D; endogenous vs exogenous vitamin D; hypocalcemia; pseudohypoparathyroidism; vitamin D dependant rickets type II; vitamin D resistant rickets