There’s more worrying news for Irish pharmaceutical firm Elan.

A new US study has found that the risk of a potentially fatal brain disorder increases as patients receive more infusions of its multiple sclerosis drug Tsyabri.

The drug , with Elan co-produces Biogen, was withdrawn from use for a time two years ago after it was first linked to the brain disorder PML.

This latest warning is based on 31 confirmed cases of the progressive infection.

Elan’s share price fell 0.6% on the New York Stock Exchange in response to the news.