Why did SARS only become an epidemic in China and in Toronto, the part of Canada where many Chinese emigrants live? Scientists have found a genetic susceptibility to SARS that explains this puzzle.

Maggie Fox writes that a variant in an immune system gene called human leukocyte antigen, or HLA, makes certain patients much more likely to develop the life-threatening symptoms of SARS. This gene variant is common in people of southern Chinese descent.

“After the outbreak of SARS coronavirus infection in the Guangdong Province of China, it was surprising to observe that the spreading of the disease was mostly confined among southern Asian populations (the Hong Kong people, Vietnamese, Singaporeans and Taiwanese),” researchers write.

Marie Lin, Chun-Hsiung Huang and her team in Taiwan examined the HLA gene in 37 cases of SARS, as well as in 28 patients who did not turn out to have SARS and 101 non-infected health care workers who were exposed to SARS. They found that patients with severe cases of SARS had a version of the HLA gene called HLA-B 4601.

No indigenous Taiwanese, who make up about 1.5% of the population there, ever developed SARS. They say, “Interestingly, (HLA-B 4601) is also seldom seen in European populations.”

During the SARS epidemic, too many people died?but what really happened to them? Whitley explores the mystery of death on this week’s Dreamland.

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