** Shares of UnitedHealth Group UNH.N down 1.2% at $339.72 premarket after WSJ reports findings of U.S. Senate's investigation into co's Medicare Advantage practices

** Senate committee alleges insurer used aggressive tactics to collect diagnoses that boost government payments under risk-adjustment rules, according to report

** In Medicare Advantage, the federal government pays insurers a fixed amount per member, with extra payments for patients with costly conditions

** Report makes no formal recommendations and alleges no wrongdoing

** UNH did not immediately respond to Reuters request for comment

** Stock fell 34.4% over the past year

(Reporting by Tharuniyaa Lakshmi in Bengaluru)

((tharuniyaa@thomsonreuters.com))