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Mild Idiopathic Infantile Hypercalcemia-Part 1: Biochemical and Genetic Findings
Nina Lenherr-Taube1, Edwin J Young2, Michelle Furman1
1Department of Pediatrics, Division of Endocrinology, The Hospital for Sick Children, University of Toronto, M5G 1X8 Toronto, Ontario, Canada.
Idiopathic infantile hypercalcemia (IIH) is a rare disorder. This study found milder forms are linked to specific gene variants and distinct vitamin D levels.
Area of Science:
- Pediatric Endocrinology
- Clinical Genetics
- Biochemistry
Background:
- Idiopathic infantile hypercalcemia (IIH) is characterized by elevated 1,25 dihydroxyvitamin D (1,25(OH)2D) and low parathyroid hormone (PTH).
- Severe IIH is linked to biallelic variants in CYP24A1 or SLC34A1 genes.
- Milder forms of IIH remain poorly understood.
Purpose of the Study:
- To characterize the genetic associations of mild IIH.
- To define the biochemical profile of mild IIH.
Main Methods:
- Cross-sectional study of 20 children (6 months–17 years) with mild IIH.
- Dietary assessment, biochemical analysis of vitamin D metabolites, and genetic analysis.
- Family member assessments offered.
Main Results:
- Elevated serum calcium, urinary calcium:creatinine ratio, and 1,25(OH)2D levels; low-normal PTH.
- Increased 1,25(OH)2D/PTH and 1,25(OH)2D/25(OH)D ratios compared to controls.
- Renal calcification in 55%; 65% had genetic variants, primarily heterozygous SLC34A1 and SLC34A3.
Conclusions:
- Mild IIH exhibits a distinct vitamin D metabolite profile.
- Heterozygous SLC34A1 and SLC34A3 variants are the primary genetic drivers of mild IIH.
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