ABSTRACT
Claudin-14 protein plays an essential role in regulating calcium ions in the kidney and ear. Two phenotypes, hearing loss and kidney stones, were reportedly associated with variations in the CLDN14 gene. This study aimed to understand CLDN14 mutations' contribution to hearing loss and renal stone formation in a Pakistani cohort. We analyzed CLDN14 sequence variations in 100 patients, along with healthy individuals, to assess whether specific polymorphisms were associated with the disease. Also, we performed an in silico analysis using a mutation database and protein annotation. The rs219779's genotype CT (p = 0.0020) and rs219780's genotype AG (p = 0.0012) were significantly associated with kidney stones. We also found that a novel haplotype, "TA" associated with kidney stone formation, has moderate linkage disequilibrium. The TA haplotype was significantly correlated with a kidney stone risk formation of 3.76-fold (OR (CI 95%) = 3.76 (1.83-7.72)) and p = 0.0016 compared to other haplotypes. In silico analysis revealed that mutations associated with hearing loss were not correlated with renal stone formation but affected claudin-14 protein stability. We structurally mapped a novel TA haplotype of CLDN14 that, based on our analysis, likely contributes to the pathogenesis of renal stones.
ABSTRACT
BACKGROUND: Nephrolithiasis (NL) affects 1 in 11 individuals worldwide and causes significant morbidity and cost. Common variants in the calcium sensing receptor gene (CaSR) have been associated with NL. Rare inactivating CaSR variants classically cause hyperparathyroidism, hypercalcemia and hypocalciuria. However, NL and familial hypercalciuria have been paradoxically associated with select inactivating CaSR variants in three kindreds from Europe and Australia. METHODS: To discover novel NL-associated CaSR variants from a geographically distinct cohort, 57 Pakistani families presenting with pediatric onset NL were recruited. The CaSR locus was analyzed by directed or exome sequencing. RESULTS: We detected a heterozygous and likely pathogenic splice variant (GRCh37 Chr3:122000958A>G; GRCh38 Chr3:12228211A>G; NM_000388:c.1609-2A>G) in CaSR in one family with recurrent calcium oxalate stones. This variant would be predicted to cause exon skipping and premature termination (p.Val537Metfs*49). Moreover, a splice variant of unknown significance in an alternative CaSR transcript (GRCh37 Chr3:122000929G>C; GRCh38 Chr3:122282082G >C NM_000388:c.1609-31G >C NM_001178065:c.1609-1G >C) was identified in two additional families. CONCLUSIONS: Sequencing of the CaSR locus in Pakistani stone formers reveals a novel loss-of-function variant, expanding the connection between the CaSR locus and nephrolithiasis.
