Carlsbad’s Ionis Pharmaceuticals and Biogen have expanded their collaboration to identify new drug candidates for the treatment of spinal muscular atrophy (SMA).

Under the new agreement, Ionis will receive a $25 million upfront payment and will earn development and regulatory milestone payments from Biogen if new drugs advance toward approval. Upon commercialization, Massachusetts-based Biogen would pay Ionis performance milestones and tiered royalties on net sales.

With this deal, Ionis and Biogen hope to build on the success of spinraza, another drug that treats SMA, which Ionis developed and Biogen commercialized. SMA is marked by the loss of motor neurons in the spinal cord and lower brain stem, and those with severe cases can become paralyzed and have difficulty with basic functions like breathing and swallowing.

“Our antisense technology uniquely positions us to work with Biogen towards delivering new therapies and expanding our experience in SMA,” said Stanley Crooke, CEO and chairman of Ionis, in a news release.