Washington, March 2 (IANS) Kidney stones afflict three out of 20 men at some stage but for some reason seem to leave mice untouched. Now researchers claim to have found why kidney stones discriminate between mice and men. Kidney stones are crystalline deposits of chemicals that should have been excreted in the urine, particularly oxalate. Common in food, it is usually disposed of by the gut into the faeces by exchanging it for chloride.

If there is little chloride available, in a low-salt diet for example, oxalate may be retained by the intestine to eventually be excreted by the kidneys, where the stones may form.

Mice, unlike men, do not spontaneously develop kidney stones, making it difficult to set up an animal model of this common disease.

The new study, the findings of which have been published in the latest issue of The Journal of Physiology, has shown that the human form of the protein responsible for secreting oxalate into the faeces requires a lot more chloride for efficient oxalate transport than the same structure in mice.

Worse still, a variant form of the protein found in some people has even further limited ability to export oxalate. Mice, it seems, are far more efficient at disposing of oxalate than humans.

Uncovering the molecular mechanisms of oxalate removal should help to develop improved treatments to prevent or even reverse the formation of kidney stones in humans.