Editorial comment.

Owing to errors made by the authors, Gavin Giovannoni and Tove Christensen, the editorial 'HERVs: have we been here before?' Multiple Sclerosis Journal 18(12): 1670-1672, (DOI: 10.1177/1352458512469331 ) is incorrect. This editorial addressing the article written by Perron and colleagues in the same issue, contained a number of errors identified by both the authors of the editorial and the authors of the article. The latter are outlined in the letter from Hervé Perron et al to follow, (DOI: 10.1177/1352458513485051) with additional supplemental information. The authors of the editorial suggested that they rewrite the entire piece to address many of the issues raised and this has also been published on the following pages.