Acknowledging the rarity of such a step, U.S. District Chief Judge Colleen McMahon of the Southern District of New York said she was compelled to break with a U.S. magistrate judge’s recommendation to allow an expert to testify in a suit over Alzheimer’s drugs.

“This is the rare case where I conclude that Magistrate Judge [James] Francis committed clear error by recommending that the Jaskot motion be denied,” McMahon wrote in a Monday order.