A breakdown of a recycling system in cells appears to be the underlying cause of a fatal nerve disease.Amyotrophic lateral sclerosis (ALS), the most common form of motor neuron disease, causes paralysis.A US team, writing in Nature, found the flaw in the way nerve cells in the brain recycle protein building blocks, which means cells cannot repair themselves and become damaged.Experts in the UK said that the findings were significant. ALS affects an estimated 350,000 people around the world, including children and adults, with about half of people dying within three years of its onset.The breakdown occurs in the recycling system in the nerve cells of the spinal cord and the brain.In order to function properly, the protein building blocks in the cells need to be recycled. But in ALS, that system is broken. The cell cannot repair or maintain itself and becomes severely damaged.The scientists found a protein, ubiquilin2, which should be directing the recycling process, does not work in people with ALS.This means the damaged proteins accumulate in nerve cells of the spinal cord and brain, causing their degeneration. The researchers, from Northwestern University Feinberg School of Medicine, found this breakdown occurs in all three forms of ALS - hereditary (familial). ALS that is not hereditary (sporadic) and ALS that targets the brain (ALS/dementia).Lead author Teepu Siddique said: \"This opens up a whole new field for finding an effective treatment for ALS. \"We can now test for drugs that would regulate this protein pathway or optimise it, so it functions as it should in a normal state.\"They also say the finding could have a role to play in other neurodegenerative diseases, including dementia and Parkinson\'s disease. Dr Belinda Cupid, head of research development at the UK\'s Motor Neurone Disease Association, said: \"This is a big news story for motor neurone disease research. \"We\'ve known for some time that the waste and recycling system in motor neurons is damaged, but this is the first time that there has been direct proof.\"This discovery provides researchers with an exciting new avenue to explore as they search for an effective treatment.\" From / BBC