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  • Title: Do the Heterozygous Carriers of a CYP24A1 Mutation Display a Different Biochemical Phenotype Than Wild Types?
    Author: Brancatella A, Cappellani D, Kaufmann M, Borsari S, Piaggi P, Baldinotti F, Caligo MA, Jones G, Marcocci C, Cetani F.
    Journal: J Clin Endocrinol Metab; 2021 Mar 08; 106(3):708-717. PubMed ID: 33249478.
    Abstract:
    CONTEXT: Human cytochrome P450 24 subfamily A member 1 (CYP24A1) loss-of-function mutations result in impaired activity of the 24-hydroxylase involved in vitamin D catabolism, thus inducing a vitamin D-dependent hypercalcemia. Homozygotes often present an overt clinical phenotype named idiopathic infantile hypercalcemia (IIH), whereas it is debated whether heterozygotes display an abnormal phenotype. OBJECTIVE: To compare the clinical and biochemical features of heterozygous carriers of CYP24A1 variant and healthy wild-type controls sharing the same genetic and environmental exposure. METHODS: A large family harboring the nonsense c.667A>T, p.Arg223* pathogenic variant in the CYP24A1 gene was evaluated. All subjects underwent clinical and biochemical evaluation and complete analysis of vitamin D metabolites using mass spectroscopy including 1,24,25(OH)3D3. Subjects were divided into 2 groups according to their genotype: heterozygotes and wild-type for the CYP24A1 variant. RESULTS: The proband, a 40-year-old man, homozygous for p.Arg223* pathogenic variant, had a history of mild hypercalcemia with a seasonal trend, recurrent nephrolithiasis, and no episodes of acute hypercalcemia. He showed the highest serum levels of fibroblast growth factor 23, the highest 25(OH)D3/24,25(OH)2D3 ratio and undetectable levels of 1,24,25(OH)3D3, which represent indicators of a loss-of-function CYP24A1. Compared with the wild-types, heterozygotes had higher serum calcium and 25(OH)D3 concentrations (P = .017 and P = .025, respectively), without any difference in the other biochemical parameters and in the rate of nephrolithiasis. CONCLUSION: Heterozygotes exhibit a biochemical phenotype different from that of wild-type subjects. In clinical practice, these individuals might require surveillance because of the potential risk of developing hypercalcemia and related clinical manifestations if exposed to triggering factors.
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