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IT MIGHT sound strange to suggest that flu is, in any sense, a hereditary illness. Classic inherited diseases, such as sickle-cell anaemia and cystic fibrosis, are caused by broken genes that come from a sufferer’s parents. Flu is caused by a virus.
A paper published in this week’s Science by Jean-Laurent Casanova of the Necker Hospital for Sick Children, in Paris, shows, though, how categories can get blurred—and emphasises the point that, however much people might like to classify things biological into the neat bins of “genes” and “environment”, nature is not so obliging. In all but the rarest of circumstances, both are involved.
The case Dr Casanova reports is of a then-two-year-old girl admitted to the Necker in 2011 with severe flu. He was one of the girl’s doctors, and her symptoms were so extreme (technically, they constituted what is known as acute respiratory distress syndrome, or ARDS), that he suspected there might be something unusual about her. He therefore sequenced her genome and, in so doing, discovered she had two broken copies (one from each parent) of the gene encoding a protein called interferon regulatory factor 7.
This protein, as its name suggests, stimulates production of interferon, an antiviral molecule. Absence of interferon made the cells lining the girl’s respiratory tract more vulnerable to...