A genetic variant in the immune system might render some groups of people more susceptible to severe acute respiratory syndrome (SARS) infection, Taiwanese researchers report.

Waiting to exhale: People in South China and Taiwan may be genetically susceptible to SARS. Credit: Richard Chung/Reuters

Marie Lin, a hematologist at the Mackay Memorial Hospital in Taipei, says subtypes of human leukocyte antigen (HLA) class I are associated with severe SARS infection.

Lin and her team compared blood samples from 65 suspected SARS patients (including 37 probable cases) with samples from 101 high-risk, uninfected health-care workers. The researchers used 190 healthy, unrelated Taiwanese individuals as controls.

People with the HLA-B*4601 allele are most likely to fall victim to SARS, the researchers reported (BMC Med. Genet. 4; 2003). Of the 37 probable cases, 15 had HLA-B*4601, and 5 severe cases had a significantly higher frequency of the allele when compared with controls. The HLA system is often used to search for the origins of infectious diseases and autoimmune disorders.

The HLA-B*4601 allele is found in about 10% of the Taiwanese population and among other southern Asians, including people from China's southern coast, Hong Kong, Singapore and part of Vietnam—areas hit hard by SARS. But it is seldom seen in the indigenous people of Taiwan—about 1.5% of the total Taiwanese population—in Caucasians or in people of African origin.

The results explain why south China was the epicenter of the SARS epidemic, the researchers suggest. The finding tallies with the scenario in Taiwan: no probable SARS cases were reported among indigenous people. It might also explain why the disease left Caucasian people largely unaffected—except in Toronto, which has a high Asian population.

Lin suggests screening health-care workers for HLA-B*4601 to prevent the spread of SARS. But other scientists are cautious about extrapolating results from a small study.

“It's too [early] to talk about mass screening now,” says Yuh-Shan Jou, a researcher in Taiwan's National Health Research Institutes. “The lack of data from other areas hit by SARS makes Lin's scientific evidence comparatively weak.”