Piper Jaffray analyst Edward Tenthoff points out that shares of Alnylam Pharmaceuticals have given back the gains since last month's Onpattro approval, and down 24% from recent highs. Yesterday's 6% drop move was driven by the Center for Drug Evaluation and Research's Multidisciplinary Review Document, which unveiled four of 148, of 2.7%, of Onpattro patients experienced atrioventricular block and received a pacemaker versus none on placebo, Tenthoff tells investors in a research note. However, the analyst says atrioventricular block is common in hereditary transthyretin amyloidosis patients as amyloid deposits in the heart block normal sinus rhythm. Importantly, all four patients remained on Onpattro and continued into the OLE study, Tenthoff writes. Further, the drug's label does not require monitoring, he adds. As such, the analyst views yesterday's selloff in shares of Alnylam as overblown. He reiterates an Overweight rating on the stock with a $160 price target.