WASHINGTON—The acting head of the Food and Drug Administration on Friday called for a government investigation into highly unusual contacts between her agency’s drug reviewers and the maker of a controversial new Alzheimer’s drug. Dr. Janet Woodcock announced the extraordinary step via Twitter. It’s the latest fallout over last month’s approval of Aduhelm, an expensive and unproven therapy that the agency OK’d against the advice of its own outside experts. Woodcock made the request to the Department of Health and Human Services’ inspector general, the watchdog agency that oversees the FDA and other federal health agencies. The move comes after numerous calls for a probe into the approval from medical experts, consumer advocates and members of Congress. Two congressional committees have already launched their own review. “We believe an independent assessment is the best manner in which to determine whether any interactions that occurred between the manufacturer and the agency’s …