title: Mutations in CYP24A1 and idiopathic infantile hypercalcemia.
abstract: BACKGROUND
  Vitamin D supplementation for the prevention of rickets is one of the oldest and most effective prophylactic measures in medicine, having virtually eradicated rickets in North America. Given the potentially toxic effects of vitamin D, the recommendations for the optimal dose are still debated, in part owing to the increased incidence of idiopathic infantile hypercalcemia in Britain in the 1950s during a period of high vitamin D supplementation in fortified milk products. We investigated the molecular basis of idiopathic infantile hypercalcemia, which is characterized by severe hypercalcemia, failure to thrive, vomiting, dehydration, and nephrocalcinosis.
  
  
  METHODS
  We used a candidate-gene approach in a cohort of familial cases of typical idiopathic infantile hypercalcemia with suspected autosomal recessive inheritance. Identified mutations in the vitamin D-metabolizing enzyme CYP24A1 were evaluated with the use of a mammalian expression system.
  
  
  RESULTS
  Sequence analysis of CYP24A1, which encodes 25-hydroxyvitamin D 24-hydroxylase, the key enzyme of 1,25-dihydroxyvitamin D(3) degradation, revealed recessive mutations in six affected children. In addition, CYP24A1 mutations were identified in a second cohort of infants in whom severe hypercalcemia had developed after bolus prophylaxis with vitamin D. Functional characterization revealed a complete loss of function in all CYP24A1 mutations.
  
  
  CONCLUSIONS
  The presence of CYP24A1 mutations explains the increased sensitivity to vitamin D in patients with idiopathic infantile hypercalcemia and is a genetic risk factor for the development of symptomatic hypercalcemia that may be triggered by vitamin D prophylaxis in otherwise apparently healthy infants.
authors.affiliation: University Children's Hospital, Muenster, Germany.
authors.forename: Karl P
authors.initials: KP
authors.lastname: Schlingmann
authors.forename: Martin
authors.initials: M
authors.lastname: Kaufmann
authors.forename: Stefanie
authors.initials: S
authors.lastname: Weber
authors.forename: Andrew
authors.initials: A
authors.lastname: Irwin
authors.forename: Caroline
authors.initials: C
authors.lastname: Goos
authors.forename: Ulrike
authors.initials: U
authors.lastname: John
authors.forename: Joachim
authors.initials: J
authors.lastname: Misselwitz
authors.forename: Günter
authors.initials: G
authors.lastname: Klaus
authors.forename: Eberhard
authors.initials: E
authors.lastname: Kuwertz-Bröking
authors.forename: Henry
authors.initials: H
authors.lastname: Fehrenbach
authors.forename: Anne M
authors.initials: AM
authors.lastname: Wingen
authors.forename: Tülay
authors.initials: T
authors.lastname: Güran
authors.forename: Joost G
authors.initials: JG
authors.lastname: Hoenderop
authors.forename: René J
authors.initials: RJ
authors.lastname: Bindels
authors.forename: David E
authors.initials: DE
authors.lastname: Prosser
authors.forename: Glenville
authors.initials: G
authors.lastname: Jones
authors.forename: Martin
authors.initials: M
authors.lastname: Konrad
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D006224:Cricetinae; D003412:Cricetulus; D004252:DNA Mutational Analysis; D005260:Female; D005808:Genes, Recessive; D056726:Genetic Association Studies; D020022:Genetic Predisposition to Disease; D006801:Humans; D006934:Hypercalcemia / Q000139:chemically induced / Q000235:genetics*; D007223:Infant; D008297:Male; D009154:Mutation; D010375:Pedigree; D012307:Risk Factors; D013250:Steroid Hydroxylases / Q000235:genetics* / Q000378:metabolism; D014807:Vitamin D / Q000009:adverse effects* / Q000378:metabolism / Q000627:therapeutic use; D065668:Vitamin D3 24-Hydroxylase
chemical_list: D014807:Vitamin D; D013250:Steroid Hydroxylases; C585549:CYP24A1 protein, human; D065668:Vitamin D3 24-Hydroxylase