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 biol...