March 10 (UPI) -- The Food and Drug Administration has approved expanded use of leucovorin calcium tablets for treating cerebral folate deficiency, a rare disorder. The vitamin, a synthetic form of vitamin B9, has been used to treat toxic side effects of chemotherapy. The FDA approval is based on "a systematic review of the published literature on the topic, including published case reports with patient-level information, as well as mechanistic data," the agency said in a press release .