title: Calcium and bone homeostasis in heterozygous carriers of CYP24A1 mutations: A cross-sectional study.
abstract: BACKGROUND
  Bi-allelic CYP24A1 mutations can cause idiopathic infantile hypercalcemia (IIH), adult-onset nephrocalcinosis, and possibly bone metabolism disturbances. It is currently unclear if heterozygous carriers experience clinical problems or biochemical abnormalities. Our objective is to gain insight in the biochemical profile and health problems in CYP24A1 heterozygotes.
  
  
  METHODS
  Cross-sectional evaluation of participants. Data of previously reported carriers are reviewed.
  
  
  METHODS
  Outpatient clinic of a tertiary care hospital. Participants were eight family members of an infant with a well-characterized homozygous CYP24A1 mutation c.1186C>T p.(Arg396Trp).
  
  
  RESULTS
  Serum vitamin D metabolites. Symptoms or biochemical signs of hypercalcemia, hypercalciuria or nephrocalcinosis. Bone health in heterozygous as compared to wild type (WT) subjects.
  
  
  METHODS
  Genotyping by Sanger sequencing; vitamin D metabolites by liquid chromatography tandem mass spectrometry; renal, calcium and bone markers by biochemical analyses; presence of nephrocalcinosis by renal ultrasound; bone health by dual-energy X-ray absorptiometry and peripheral quantitative computed tomography.
  
  
  RESULTS
  Six participants were heterozygous carriers of the mutation. None of the heterozygous subjects had experienced IIH. One had a documented history of nephrolithiasis, two others had complaints compatible with this diagnosis. No major differences between WT and heterozygous subjects were found regarding bone health, serum or urinary calcium or 25OHD/24,25(OH)2D ratio. Literature reports on three out of 33 heterozygous cases suffering from IIH. In all three, the 25OHD/24,25(OH)2D ratio was highly elevated. Nephrocalcinosis was frequently reported in family members of IIH cases.
  
  
  CONCLUSIONS
  Small sample size, lack of a large control group.
  
  
  CONCLUSIONS
  Our and literature data suggest that most heterozygous CYP24A1 mutation carriers have a normal 25OHD/24,25(OH)2D ratio, are usually asymptomatic and have a normal skeletal status but may possibly be at increased risk of nephrocalcinosis. A review of the available literature suggests that an elevated 25OHD/24,25(OH)2D ratio may be associated with symptoms of IHH, irrespective of carrier status.
authors.affiliation: Department of Pediatrics, Division of Pediatric Endocrinology, Ghent University Hospital and Ghent University, De Pintelaan 185, 9000 Ghent, Belgium. Electronic address: martine.cools@ugent.be.
authors.forename: M
authors.initials: M
authors.lastname: Cools
authors.affiliation: Unit for Osteoporosis and Metabolic Bone Disease, Department of Rheumatology and Endocrinology, Ghent University Hospital and Ghent University, De Pintelaan 185, 9000 Ghent, Belgium. Electronic address: stefan.goemaere@ugent.be.
authors.forename: S
authors.initials: S
authors.lastname: Goemaere
authors.affiliation: Center for Medical Genetics, Ghent University Hospital and Ghent University, De Pintelaan 185, 9000 Ghent, Belgium. Electronic address: dorien.baetens@ugent.be.
authors.forename: D
authors.initials: D
authors.lastname: Baetens
authors.affiliation: Department of Pediatrics, Division of Pediatric Nephrology, Ghent University Hospital and Ghent University, De Pintelaan 185, 9000 Ghent, Belgium. Electronic address: ann.raes@ugent.be.
authors.forename: A
authors.initials: A
authors.lastname: Raes
authors.affiliation: Department of Pediatrics, Division of Pediatric Endocrinology, Ghent University Hospital and Ghent University, De Pintelaan 185, 9000 Ghent, Belgium. Electronic address: an.desloovere@uzgent.be.
authors.forename: A
authors.initials: A
authors.lastname: Desloovere
authors.affiliation: Department of Endocrinology, Ghent University Hospital and Ghent University, De Pintelaan 185, 9000 Ghent, Belgium. Electronic address: jean.kaufman@ugent.be.
authors.forename: J M
authors.initials: JM
authors.lastname: Kaufman
authors.affiliation: Department of Pediatrics, Division of Pediatric Endocrinology, Ghent University Hospital and Ghent University, De Pintelaan 185, 9000 Ghent, Belgium. Electronic address: jean.deschepper@uzgent.be.
authors.forename: J
authors.initials: J
authors.lastname: De Schepper
authors.affiliation: Department of Laboratory Medicine, Leuven University Hospitals, Herestraat 49, 3000 Leuven, Belgium. Electronic address: ivo.jans@uzleuven.be.
authors.forename: I
authors.initials: I
authors.lastname: Jans
authors.affiliation: Department of Laboratory Medicine, Leuven University Hospitals, Herestraat 49, 3000 Leuven, Belgium; Department of Clinical and Experimental Endocrinology, Leuven University Hospital and Leuven University, Herestraat 49, 3000 Leuven, Belgium. Electronic address: dirk.vanderschueren@med.kuleuven.be.
authors.forename: D
authors.initials: D
authors.lastname: Vanderschueren
authors.affiliation: Department of Laboratory Medicine, Leuven University Hospitals, Herestraat 49, 3000 Leuven, Belgium. Electronic address: jaak.billen@uzleuven.be.
authors.forename: J
authors.initials: J
authors.lastname: Billen
authors.affiliation: Center for Medical Genetics, Ghent University Hospital and Ghent University, De Pintelaan 185, 9000 Ghent, Belgium. Electronic address: elfride.debaere@ugent.be.
authors.forename: E
authors.initials: E
authors.lastname: De Baere
authors.affiliation: Department of Hormonology, Ghent University Hospital, De Pintelaan 185, 9000 Ghent, Belgium. Electronic address: tom.fiers@uzgent.be.
authors.forename: T
authors.initials: T
authors.lastname: Fiers
authors.affiliation: Department of Clinical and Experimental Endocrinology, Leuven University Hospital and Leuven University, Herestraat 49, 3000 Leuven, Belgium. Electronic address: roger.bouillon@med.kuleuven.be.
authors.forename: R
authors.initials: R
authors.lastname: Bouillon
mesh_terms: D015502:Absorptiometry, Photon; D001842:Bone and Bones / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002853:Chromatography, Liquid; D003430:Cross-Sectional Studies; D004100:Dihydroxycholecalciferols / Q000097:blood; D005260:Female; D005838:Genotype; D006579:Heterozygote; D006706:Homeostasis / Q000235:genetics; D006801:Humans; D006934:Hypercalcemia / Q000453:epidemiology / Q000235:genetics; D053565:Hypercalciuria / Q000453:epidemiology / Q000235:genetics; D015994:Incidence; D008297:Male; D009154:Mutation; D009397:Nephrocalcinosis / Q000453:epidemiology / Q000235:genetics; D053040:Nephrolithiasis / Q000453:epidemiology / Q000235:genetics; D010375:Pedigree; D053719:Tandem Mass Spectrometry; D065668:Vitamin D3 24-Hydroxylase / Q000235:genetics*
chemical_list: D004100:Dihydroxycholecalciferols; C585549:CYP24A1 protein, human; D065668:Vitamin D3 24-Hydroxylase; D002118:Calcium
keywords: CYP24A1; Heterozygous; Idiopathic infantile hypercalcemia; Mutation; Nephrocalcinosis; Nephrolithiasis