Genetic variations transform mild influenza to a life threatening disease

Genetic variations in human body make it more susceptible to diseases. A genetic finding explains why influenza becomes a life-threating disease to some people while it has only mild effects in others.

Researchers identified for the first time a human gene that influences how we respond to influenza infection.

People who carry a particular variant of a gene called IFITM3 are significantly more likely to be hospitalised when they fall ill with influenza than those who carry other variants.

This gene plays a critical role in protecting the body against infection with influenza and a rare version of it appears to make people more susceptible to severe forms of the disease. The results are published in the journal Nature.

A central question about viruses is why some people suffer badly from an infection and others do not. IFITM3 is an important protein that protects cells against virus infection and is thought to play a critical role in the immune system’s response against such viruses as H1N1 pandemic influenza, commonly known as ‘swine flu’. When the protein is present in large quantities, the spread of the virus in lungs is hindered, but if the protein is defective or absent, the virus can spread more easily, causing severe disease.

The antiviral role of IFITM3 in humans was first suggested by studies using a genetic screen, which showed that the protein blocked the growth of influenza virus and dengue virus in cells. This led the team to ask whether IFITM3 protected mice from viral infections. They removed the IFITM3 gene in mice and found that once they contracted influenza, the symptoms became much more severe compared to mice with IFITM3. In effect, they found the loss of this single gene in mice can turn a mild case of influenza into a fatal infection.

The researchers then sequenced the IFITM3 genes of 53 patients hospitalised with influenza and found that some have a genetic mutant form of IFITM3, which is rare in normal people. This variant gene makes cells more susceptible to viral infection.

This research is important for people who have this variant as we predict their immune defences 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.

Source: Wellcome Trust Sanger Institute, UK



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