WASHINGTON, Feb. 29 (Xinhua) -- Researchers have identified a rare gene mutation associated with some cases of amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease.

    These findings, published Friday in the journal Science, may help researchers learn more about the processes that lead to this fatal adult-onset motor neuron disorder.

    The first ALS-related gene mutation SOD1 was found in 1993, but it affects only 1 percent of all ALS patients. Now, after a long dry spell, researchers have finally hit on a second. It's just as rare as the first, but it seems to be more closely related to aspects of ALS pathology found in all patients.

    ALS can slowly destroy the motor neurons used to control muscles. Five percent of all adult-onset ALS cases are known to have a strong genetic component, affecting multiple family members. But the rest seem to appear spontaneously in people with no prior family history. Scientists know little about what causes these sporadic cases.

    Christopher Shaw, a neurologist at King's College London in the United Kingdom, started hunting for other ALS genes by recruiting patients who have the inherited form of the disease but not the SOD1 mutation.

    While screening 154 people with familial ALS, Shaw and his colleagues found four individuals in one family who shared the same mutation: a single changed base on chromosome 1. The base was located in the TDPB gene, which encodes a protein called TDP-43 whose function isn't clear.

    To see whether TDPB might have a role beyond inherited ALS, Shaw's team sequenced the TDPB gene in 200 people from U.K. and 172 from Australia with the sporadic form of the disease. They found two more people with different mutations in the same gene and didn't see it in more than 1200 people without ALS. Finding multiple mutations in the same gene is "pretty rare," says Shaw.

    All the mutations seem to have the same effect. When they created chicken embryos with a mutated TDPB gene, they found that some neurons and other cells died. Shaw's next step is to insert this faulty TDPB gene into mice and see if it kills neurons in mammals.

    Brian Dickie, director of research development at the Motor Neurone Disease Association in U.K., believes that these mouse models may offer other insights into ALS, too.

    "TDP-43 is also deposited in the neurons of people who have dementia," he says, "and, in a small number of ALS cases, dementia precedes loss of motor function." He wonders if Shaw's work will provide a better understanding not only of ALS mechanisms but also of common pathways between ALS and other neurologic diseases.