title: Vitamin D action:  lessons learned from hereditary 1,25-dihydroxyvitamin-D-resistant rickets patients.
abstract: OBJECTIVE
  Hereditary 1,25-dihydroxyvitamin-D [1,25(OH)(2)D(3)]-resistant rickets (HVDRR) is a rare genetic disease caused by generalized resistance to 1,25(OH)(2)D(3). Less than 100 cases are reported in the literature. These patients provide an experiment by nature enabling us to understand the role of vitamin D, especially in light of the ongoing debate concerning normal vitamin D levels and the supplement dosage that should be recommended. This article summarizes the role of vitamin D in calcium absorption, rennin-angiotensin system (RAS), and cardiac state in HVDRR patients.
  
  
  RESULTS
  The precise spectrum of vitamin D activities can now be better evaluated by critical analysis of mouse models with targeted deletion of the gene encoding the vitamin D receptor (VDR). Of special interest is the unraveling of the role of VDR in calcium absorption and cardiac status in VDR-knockout mice. The facts that VDR-knockout mice up-regulate intestinal calcium absorption and skeletal mineralization independently of the VDR during pregnancy and lactation point to the existence of VDR-independent mechanisms that are involved in calcium absorption. The observation that mice with genetic disruption of the 1α-hydroxylase gene or of the VDR gene have an overstimulated RAS and consequently develop high blood pressure and cardiac hypertrophy raised concern about potential risks to the cardiovascular system in HVDRR patients.
  
  
  CONCLUSIONS
  The current review summarizes the new understanding of the effects of vitamin D on calcium absorption, the RAS, and heart hypertrophy derived from studying HVDRR patients from infancy to their mid-30s.
authors.affiliation: Pediatric Endocrinology, Meyer Children's Hospital, Rambam Healthcare Campus, Haifa, Israel. d_tiosano@rambam.health.gov.il
authors.forename: Dov
authors.initials: D
authors.lastname: Tiosano
authors.forename: Vardit
authors.initials: V
authors.lastname: Gepstein
mesh_terms: D000367:Age Factors; D000818:Animals; D002118:Calcium / Q000378:metabolism; D019587:Dietary Supplements; D053098:Familial Hypophosphatemic Rickets / Q000188:drug therapy* / Q000235:genetics / Q000503:physiopathology; D005260:Female; D000089703:Fibroblast Growth Factor-23; D005346:Fibroblast Growth Factors / Q000187:drug effects* / Q000235:genetics; D006801:Humans; D007408:Intestinal Absorption / Q000187:drug effects*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009206:Myocardium / Q000473:pathology; D011247:Pregnancy; D012084:Renin-Angiotensin System / Q000187:drug effects* / Q000235:genetics; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D014807:Vitamin D; D005346:Fibroblast Growth Factors; C097949:1,25-dihydroxyvitamin D; D000089703:Fibroblast Growth Factor-23; D002118:Calcium