The IFITM3 gene has been shown to be important for host defences against viruses. Researchers found that Ifitm3 knockout mice show an increase in serious symptoms when challenged with flu virus. Sequencing of the IFITM3 gene from patients in hospital due to flu infection showed that a statistically significant number carried a flawed IFITM3 variant. For more on this story, see www.bbc.co.uk/news/health-17474197.