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Mystery of kidney stone solved

 A new study has provided evidence to explain why some people are more prone to developing kidney stones than others

The research was conducted in mice. Because kidneys function the same way in mice as in humans, the new findings can help scientists understand the root causes of kidney stones in patients.

Most kidney stones form when the urine becomes too concentrated, allowing minerals like calcium to crystallize and stick together. Diet plays a role in the condition — not drinking enough water or eating too much salt (which binds to calcium) also increases the risk of stones.

But genes are partly to blame. A common genetic variation in a gene called claudin-14 recently has been linked to a substantial increase in risk — roughly 65 percent — of getting kidney stones. In the new study, the researchers have shown how alterations in the gene’s activity influence the development of stones.

Typically, the claudin-14 gene is not active in the kidney. The new research shows that its expression is dampened by two snippets of RNA, a sister molecule of DNA, that essentially silence the gene.

When claudin-14 is idled, the kidney’s filtering system works like it’s supposed to. Essential minerals in the blood like calcium and magnesium pass through the kidneys and are reabsorbed back into the blood, where they are transported to cells to carry out basic functions of life.

But when people eat a diet high in calcium or salt and don’t drink enough water, the small RNA molecules release their hold on claudin 14. An increase in the gene’s activity prevents calcium from re-entering the blood, the study showed.

Hou and his team have found that claudin-14 blocks calcium from entering passageways called tight junctions in cells that line the kidney and separate blood from urine.

Without a way back to the bloodstream, excess calcium goes into the urine. Too much calcium in the urine can lead to stones in the kidneys or bladder. Intense pain develops when a large stone gets stuck in the bladder, ureter or urethra and blocks the flow of urine.

This research supports the theory that people with a common variation in claudin-14 lose the ability to regulate the gene’s activity, increasing the risk of kidney stones.

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