Scientists have discovered a gene that could help explain why some people are more susceptible to flu than others.

Researchers from the Edinburgh University conducted a DNA analysis of 60 flu patients in intensive care and found that those people had an unusually high number of a gene variant called IFITM3, which influenced how they responded to flu infections, explaining why the virus is life-threatening to some while others were unaware they had been infected.

People who carry a variant of the IFITM3 gene are significantly more likely to be hospitalized when they contract the flu, compared to those who carry other variants of the gene, the scientists explained because this gene appeared to be a crucial first line of defense against influenza.

Researchers said that when the IFITM3 protein is present in large amounts, the spread of the flu virus in the lungs is hindered because it stops many forms of the virus from invading cells. However, if the protein is mutated or absent, the virus can very easily spread penetrating deeper into the lungs and replicating 10 times more, leading to severe disease like pneumonia.

"Since IFITM3 appears to be a first line defender against infection, our efforts suggest that individuals and populations with less IFITM3 activity may be at increased risk during a pandemic and that IFITM3 could be vital for defending human populations against other viruses such as avian influenza virus and dengue virus" co-senior author Dr. Abraham Brass of Ragon Institute said in a statement released on Sunday.

The findings may explain why the 2009 H1N1 influenza pandemic or “swine flu” was mild for most people, but life-threatening or deadly for others, and could potentially help doctors screen patients to identify and give priority vaccination to those who are more susceptible to the flu.

"Our research is important for people who have this variant as we predict their immune defenses could be weakened to some virus infections. Ultimately as we learn more about the genetics of susceptibility to viruses, then people can take informed precautions, such as vaccination to prevent infection," co-researcher Professor Paul Kellam of the Wellcome Trust Sanger Institute said in a statement.

Researchers said that while the genetic mutation is typically rare, it was 19 time more prevalent than expected in people who needed hospital treatment.

“While most people who may contract flu during a pandemic will recover well and not experience serious symptoms, some develop a catastrophic and potentially fatal illness and need to be treated in intensive care. This happens to otherwise healthy, young people. This study shows for the first time it may be because they are more genetically susceptible to the virus,” Dr. Kenneth Baillie, an expert in genetics and critical care at Edinburgh University's Roslin Institute said in a statement.

The study was published on Sunday in the journal Nature.