What happened

Shares of Ionis Pharmaceuticals (IONS -0.82%), 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.

An unhappy group of scientists.

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 (BIIB 0.23%). 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 (RHHBY 0.49%) 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.