What happened Shares of Ionis Pharmaceuticals (NASDAQ: IONS), a biotechnology company, have fallen around 13.6% since their closing price on Friday, Oct. 15, 2021. Investors were disappointed by phase 3 clinical trial results for tofersen, an experimental treatment for amyotrophic lateral sclerosis. So what Treatment with tofersen was supposed to help reduce physical symptoms of ALS, a progressive neurodegenerative disorder that affects around 20,000 new U.S. patients annually. The experimental treatment was aimed at an even smaller subpopulation of ALS patients, those who have SOD1 mutations. Image source: Getty Images. Treatment with tofersen lowered SOD1 protein levels, but this didn't lead to improved scores on the revised amyotrophic lateral sclerosis functional rating scale. The losses would have been much worse for Ionis Pharmaceuticals, but tofersen is being developed in a partnership with Biogen (NASDAQ: BIIB). The big biotech sponsored the failed study, so the losses to Ionis Pharmaceuticals' reputation were more severe than the financial setback. Now what Ionis and Biogen aren't giving up on the SOD1-reduction approach. In May, Biogen began another phase 3 trial with tofersen in ALS patients in an earlier stage of the disease. This was the second big clinical trial flop for Ionis Pharmaceuticals this year. In March, the biotech stock plummeted after a Huntington's disease drug developed in a partnership with Roche (OTC: RHHBY) met an untimely end. Following two high-profile flops in less than a year, it might be best to watch Ionis Pharmaceuticals and its struggling neuroscience pipeline from afar. At least until the company can tell us about a big clinical trial that succeeds. 10 stocks we like better than Ionis PharmaceuticalsWhen our award-winning analyst team has a stock tip, it can pay to listen. After all, the newsletter they have run for over a decade, Motley Fool Stock Advisor, has tripled the market.* They just revealed what they believe are the ten best stocks for investors to buy right now... and Ionis Pharmaceuticals wasn't one of them! That's right -- they think these 10 stocks are even better buys. See the 10 stocks *Stock Advisor returns as of October 20, 2021 Cory Renauer has no position in any of the stocks mentioned. The Motley Fool owns shares of and recommends Ionis Pharmaceuticals. The Motley Fool has a disclosure policy.Source