The FDA approved Qalsody (tofersen), a drug intended to treat amyotrophic lateral sclerosis with a rare mutation called the superoxide dismutase 1 gene, on April 25.
The agency said it predicts fewer than 500 ALS cases have the gene mutation, SOD1-ALS, which "attacks and kills the nerve cells that control voluntary muscles."
Qalsody is approved to be administered through spinal injection by healthcare workers who are experienced in the process.
Its approval follows a study that found "nominally significant reductions in plasma [neurofilament light chain] concentration" compared to the placebo group, the FDA said. Neurofilaments are released from damaged neurons and act as a marker for neurodegeneration, meaning the drug could have a clinical benefit, according to Biogen, the ALS drug's maker.
Biogen is conducting research to confirm the drug's efficacy because the therapy was approved via the FDA's accelerated pathway.