Swiss drugmaker Novartis on Sunday said it agreed to acquire US biotech firm Avidity Biosciences for about $12 billion in cash, as the company looks to bolster its portfolio of treatments for rare muscle disorders.Avidity stockholders will receive$72 per share in cash, representing a premium of 46% to the company’s closing on Friday.Novartis has been proactively striking deals this year to address the impending patent cliff for some of its blockbuster drugs, including Entresto for heart failure, Xolair for ...