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Medientyp: E-Artikel Titel: Improved Screening Test for Idiopathic Infantile Hypercalcemia Confirms Residual Levels of Serum 24,25-(OH)2D3 in Affected Patients Beteiligte: Kaufmann, Martin; Morse, Nicole; Molloy, Billy Joe; Cooper, Donald P; Schlingmann, Karl Peter; Molin, Arnaud; Kottler, Marie Laure; Gallagher, J Christopher; Armas, Laura; Jones, Glenville Erschienen: Oxford University Press (OUP), 2017 Erschienen in: Journal of Bone and Mineral Research, 32 (2017) 7, Seite 1589-1596 Sprache: Englisch DOI: 10.1002/jbmr.3135 ISSN: 1523-4681; 0884-0431 Entstehung: Anmerkungen: Beschreibung: <jats:title>ABSTRACT</jats:title> <jats:sec> <jats:title> </jats:title> <jats:p>CYP24A1 mutations are now accepted as a cause of idiopathic infantile hypercalcemia (IIH). A rapid liquid-chromatography tandem mass spectrometry (LC-MS/MS)-based blood test enabling measurement of the 25-OH-D3:24,25-(OH)2D3 ratio (R) can identify IIH patients on the basis of reduced C24-hydroxylation of 25-OH-D3 by CYP24A1 in vivo. Although values of this ratio are significantly elevated in IIH, somewhat surprisingly, serum 24,25-(OH)2D3 remains detectable. The current study explores possible explanations for this including: residual CYP24A1 enzyme activity in individuals with certain CYP24A1 genotypes, expression of alternative C24-hydroxylases, and the possibility of isobaric contamination of the 24,25-(OH)2D3 peak on LC-MS/MS. We employed an extended 20-min run time on LC-MS/MS to study serum vitamin D metabolites in patients with IIH due to mutations of CYP24A1 or SLC34A1; in unaffected heterozygotes and dialysis patients; in patients with vitamin D deficiency; as well as in normal subjects exhibiting a broad range of 25-OH-D levels. We identified 25,26-(OH)2D3 as a contaminant of the 24,25-(OH)2D3 peak. In normals, the concentration of 24,25-(OH)2D3 greatly exceeds 25,26-(OH)2D3; however, 25,26-(OH)2D3 becomes more significant in IIH with CYP24A1 mutations and in dialysis patients, where 24,25-(OH)2D3 levels are low when CYP24A1 function is compromised. Mean R in 30 IIH-CYP24A1 patients was 700 (range, 166 to 2168; cutoff = 140) as compared with 31 in 163 controls. Furthermore, patients possessing CYP24A1 L409S alleles exhibited higher 24,25-(OH)2D3 levels and lower R (mean R = 268; n = 8) than patients with other mutations. We conclude that a chromatographic approach which resolves 24,25-(OH)2D3 from 25,26-(OH)2D3 produces a more accurate R that can be used to differentiate pathological states where CYP24A1 activity is altered. The origin of the residual serum 24,25-(OH)2D3 in IIH patients appears to be multifactorial. © 2017 American Society for Bone and Mineral Research.</jats:p> </jats:sec> Zugangsstatus: Freier Zugang