A particular genetic fault could be responsible for a breakdown in the normal working of heart muscle, say scientists.

It could hold the key to an inherited form of heart failure in which the heart becomes too large and cannot function properly.

This enlargement of the heart, called cardiomyopathy, is often the result of the organ being continuously overworked, perhaps as the result of high blood pressure or the slow recovery from a heart attack.

At these times, the muscles of the heart are being stretched outwards under greater than normal force.

If someone deliberately did this to another muscle - for example by lifting weights - the normal response would be the growth of extra muscle to compensate.

When the heart is under stress, it also adapts to prevent itself from being injured by the extra effort.

Mechanism

The scientists, from the University of California at San Diego, have found a mechanism by which the heart protects itself when under these stresses.

If it can't do this, then cardiomyopathy may be the result.

A particular body chemical, called MLP, seems to stop the heart muscle suffering injury when under stress, and helps it contract and relax normally.

When mice were bred with a defect in the gene that produces MLP, the result was heart enlargement and reduced efficiency.

These are similar symptoms to those suffered by people with an inherited form of cardiomyopathy which is occasionally found in northern Europe.

The San Diego scientists believe that a form of gene therapy may be able to correct their heart problem in future.

The research was published in the journal Cell.