Roche’s CellCept and Novartis’ Myfortic, which are used to be prevent organ rejection, could be linked to a rare central nervous system disorder, called progressive multifocal leukoencephalophy, or PML, which is potentially fatal.

In on its web site, the FDA says Roche is aware of transplant patients who have developed PML and last November gave the agency an evaluation of PML cases and proposed new prescribing info for the labeling. Last month, Roche informed the FDA of a Dear Doctor distributed in Europe in February. Roche also received reports of PML in patients with the autoimmune disorder lupus, although CellCept is not cleared for that condition, according to the agency.

The FDA didn’t disclose the number of PML cases were reported by Roche, but has asked Novartis for related data. CellCept, also known as mycophenolate mofetil, is approved to help prevent heart, liver, and kidney transplant rejection, while Myfortic, or mycophenolic acid, is cleared to prevent kidney transplant rejection.