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LONDON (Reuters) - Researchers have found four new genetic variants that increase the risk of contracting one of the major forms of leukemia, confirming that risk factors for the fatal blood cancer can be inherited.The findings mean scientists now know of 10 genetic variants associated with chronic lymphocytic leukemia (CLL), scientists at Europe's Institute of Cancer Research who conducted the study said.The four new genetic factors are all common in European populations and each factor contributes to an increase in the risk of the disease.CLL is the most common type of leukemia in adults, accounting for around 30 to 40 percent of all forms of leukemia in Western countries. Most of those diagnosed are over the age of 55, and while the incidence of CLL is broadly equal in black and white populations, the disease is rare among Asians.Richard Houlston, who led the study, said it confirmed the inherited risk of CLL, and showed it was not due to a single gene due to the cumulative effect of many genetic changes.Each person may carry any number, from a few of the identified risk factors to all of them, he said in research published in the journal Nature Genetics. And the more genetic factors carried, the higher their risk of developing CLL."People who have more than 13 risk factors are seven times more likely than the general population to develop CLL," Houlston added in a statement about the study.The risk factors were identified using a genetic analysis technique that scientists have used previously to find risk genes in breast, prostate, testes, brain and colon cancer and childhood leukemia.The researchers scanned the genes of 2,503 CLL patients and compared them to 5,789 healthy people, looking for differences in DNA between the two groups.In previous studies, Houlston's team found that genetic factors could make people more susceptible to CLL, identifying six genetic factors more common among sufferers.The four new factors add to those findings and the study also found that 87 percent of people with CLL would have at least one of these genetic risks.David Grant, scientific director of the Leukemia Research charity which funded the study, said it confirmed some long-held suspicions that this form of leukemia may run in families."This research is providing the genetic evidence that an increased risk of developing CLL can be inherited," he said in a statement."However it is clearly a complex picture and we need to study more families before we can be certain of the particular genetic traits that are most important."