LOS ANGELES, Nov. 1 (Xinhua) -- U.S. researchers have identified four genes which may be linked to the most common form of the late-onset Alzheimer's disease, a new study showed.

    The four new genes were discovered after researchers conducted a gene scan of hundreds of families with a history of the devastating neurological disorder, said the study by the Massachusetts General Hospital-Mass General Institute for Neurological Disease (MGH-MIND).

An Alzheimer's patient is seen in a handout image from the ITV documentary "Malcolm and Barbara: Love's Farewell", released to Reuters on Aug. 1, 2007. U.S. researchers have identified four genes which may be linked to the most common form of the late-onset Alzheimer's disease, a new study showed. (Xinhua/Reuters File Photo) Photo Gallery>>>

    The researchers first tested about half a million DNA markers in samples collected from more than 400 families with at least three Alzheimer's patients.

    Five markers were revealed to exhibit genetic associations with Alzheimer's including the Apolipoprotein E (APOE), the only gene proven to increase risk of the late-onset Alzheimer's disease.

    To confirm the four new markers, the researchers analyzed samples from 900 additional families with a history of Alzheimer's and got the strongest marker on chromosome 14.

    "The genetic association of Alzheimer's with this novel chromosome 14 gene, which like APOE appears to influence age of onset, is sufficiently strong to warrant intensive follow-up investigations into its role in the process of nerve cell death in this disease," said the study leader Rudolph Tanzi, director of the genetics and aging research unit at the MGH-MIND.

    Another newly-identified marker is a gene known to cause a movement disorder called spinocerebellar ataxia, which involves the death of nerve cells in other parts of the central nervous system.

    The third is a gene involved in the innate immune system (part of the body's defense against bacteria and viruses) and the fourth is a gene that produces a synaptic protein.

    The findings, published in the November issue of the American Journal of Human Genetics, are the first results of the Alzheimer's Genome Project supported by the Cure Alzheimer's Fund and the U.S. National Institutes of Mental Health.

    "Virtually all current research into therapies is based on the Alzheimer's genes that we already know about; so each new gene we find not only enhances our ability to predict and diagnose the disease, but also provides valuable new clues about biochemical events and pathways involved in the disease process," Tanzi said.