Under the influence

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.