Searchable abstracts of presentations at key conferences in endocrinology
Endocrine Abstracts (2009) 19 P7

SFEBES2009 Poster Presentations Bone (21 abstracts)

A mouse model, Hcalc1, for autosomal dominant hypercalciuria is due to a transient receptor potential cation channel, subfamily V, member 5 (Trpv5) mutation

N Loh 1 , M Stechman 1 , B Ahmad 1 , F Hannan 1 , T Hough 2 , K-P Chiev 2 , M Stewart 2 , L Bentley 3 , R Cox 3 , S Brown 3 & R Thakker 1

1University of Oxford, Oxford, Oxfordshire, UK; 2Mary Lyon Centre, Medical Research Council, Harwell, Oxfordshire, UK; 3MRC Mammalian Genetics Unit, Medical Research Council, Harwell, Oxfordshire, UK.

To identify genes causing hypercalciuria, we screened male offspring of C57BL/6J male mice mutagenised by N-ethyl-N-nitrosourea (ENU) for this abnormality. Mice were kept in accordance with UK Home Office welfare guidelines and project licence restrictions. Metabolic cage studies were performed to collect 24-hour urine samples, and this revealed one mouse with hypercalciuria (Hcalc1). Inheritance testing demonstrated that Hcalc1 was inherited as an autosomal dominant trait. A genome-wide search using chromosome-specific sets of 60 single nucleotide polymorphisms (SNPs), at 20–30 cm intervals, and DNA from 13 mice (10 affected, 3 unaffected) revealed co-segregation of Hcalc1 and chromosome 6 SNPs (peak LOD score=3.91 at 0% recombination). An extended analysis in 89 mice (39 affected, 50 unaffected) using an additional 6 SNPs demonstrated co-segregation of Hcalc1 with loci from chromosome 6B1/B2 and yielded a peak LOD score of 26.8 at 0% recombination. An analysis of recombinants defined a critical 11.94-Mbp region that contained 176 genes, amongst which were those for transient receptor potential cation channel, subfamily V, member 5 (Trpv5) and 6 (Trpv6). Trpv5 and Trpv6 are involved in vitamin D-regulated calcium transport in the kidney and gastrointestinal tract, respectively. DNA sequence analysis of both Trpv5 and Trpv6 was therefore undertaken. This identified a T>C transition in codon 682 of Trpv5 that altered a wildtype serine to a mutant proline. This T>C transition resulted in a gain of a BsaJI site, which was used to confirm the mutation in the hypercalciuric mice, and its absence in normocalciuric mice. The mean 24-hour urine calcium creatinine ratio in the mutant hypercalciuric (n=39) versus wildtype normocalciuric (n=50) mice was significantly higher (1.88±1.01 versus 0.17±0.07, P<0.0001). Plasma calcium, phosphate, and other electrolytes were similar in the hypercalciuric and normocalciuric mice. Thus, we have established a mouse model for autosomal dominant hypercalciuria due to a Trpv5 Ser682Pro mutation.

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