Editors of the journal Science have asked the co-authors of a 2009 paper that linked chronic fatigue syndrome to a retrovirus called XMRV to voluntarily retract the paper.

But in written response Friday, study co-author Judy A. Mikovits of the Whittemore Peterson Institute for Neuro-Immune Disease said "it is premature to retract our paper." The letter was reviewed by the The Wall Street Journal.

The...