Abstract
Summary
Mutations of the CYP24A1 gene can result in hypercalcemia, hyerpercalciuria, and nephrolithiasis, but disease severity is variable. Clinical and biochemical phenotypes were correlated with gene sequence information in a family with two CYP24A1 mutations. A gene dose effect was apparent with monoallelic mutations demonstrating milder disease manifestations than biallelic mutations.
Introduction
The objective was to examine the spectrum of clinical and biochemical phenotypes in a family with monoallelic and biallelic mutations of CYP24A1 after identification of the proband with two mutations of the CYP24A1 gene: (A) p.R396W and (B) E143del-Het.
Methods
Clinical and biochemical phenotypes were correlated with CYP24A1 sequence information in the proband and four siblings, a daughter, and two nieces of the proband. The subjects’ medical histories were evaluated, and measurement of serum minerals, vitamin D metabolites, PTH, bone turnover markers, and urinary calcium and sequencing of the CYP24A1 gene were performed.
Results
The proband had nephrolithiasis, osteopenia, hypercalcemia, hypercalciuria, elevated serum 1,25(OH)2D, undetectable 24,25(OH)2D, and inappropriately low PTH concentrations. Two subjects with biallelic (A/B) mutations had nephrolithiasis, marked hypercalciuria (583 ± 127 mg/24 h, mean ± SD), compared with five subjects with monoallelic mutations (A or B) with a urine calcium of 265 ± 85 mg/24 h. Two subjects with monoallelic mutations had nephrolithiasis and one had non-PTH dependent hypercalcemia. Five subjects had high 1,25(OH)2D measurements, including three with monoallelic mutations. The 25OHD/24,25(OH)2D ratio, in subjects with biallelic mutations was 291 versus 19.8 in the subjects with monoallelic mutations.
Conclusions
In this family, adults with CYP24A1 mutations a gene dose effect is apparent: subjects with biallelic, compound heterozygous mutations (A/B) have a more severe clinical and biochemical phenotype, whereas, subjects with monoallelic mutations demonstrate milder disease manifestations which are not easily characterized through biochemical assessment.
Abbreviations
- 25-Hydroxyvitamin D:
-
25(OH)D
- 1,25-Dihydroxyvitamin D:
-
1,25(OH)2D
- 24,25-Dihydroxyvitamin D:
-
24,25(OH)2D
- ACE:
-
Angiotensin-converting enzyme
- B-CTx:
-
Carboxyterminal cross-linking telopeptide of bone collagen
- PCR:
-
Polymerase chain reaction
- PTH:
-
Parathyroid hormone
- TSH:
-
Thyroid stimulating hormone
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Acknowledgments
Study design: DOK, RW, and PT. Study conduct: DOK; data collection: DOK; data analysis: DOK, RW, PT, and RK; data interpretation: DOK, RW, PT, RK, RS, and YW; drafting manuscript: DOK, RW, and PT; revising manuscript content: RK, RS, and YW; approving final version of manuscript: DOK, PT, and RW. DOK takes responsibility for the integrity of the data analysis.
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This study was made possible using the resources of CTSA Grant Number UL1 TR000135 from the National Center for Advancing Translational Science (NCATS).
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Derek O’Keeffe, Peter Tebben, Rajiv Kumar, Ravinder Singh, Yanhong Wu, and Robert Wermers state that they have no conflicts of interest.
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O’Keeffe, D.T., Tebben, P.J., Kumar, R. et al. Clinical and biochemical phenotypes of adults with monoallelic and biallelic CYP24A1 mutations: evidence of gene dose effect. Osteoporos Int 27, 3121–3125 (2016). https://doi.org/10.1007/s00198-016-3615-6
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DOI: https://doi.org/10.1007/s00198-016-3615-6