Ironwood is branching out into rare disease

Ironwood Pharmaceuticals, the Cambridge biotech behemoth known for drugs that treat gastrointestinal disorders, is now spinning off a new startup in the rare disease space. GI drugs may be losing a bit of their lusters, according to analysts, whereas the rare disease space remains lucrative.

The new company, called Cyclerion Therapeutics, has five drug development programs in the works — working on sickle cell disease and other life-threatening, but uncommon, diseases of the central nervous system, liver, and lungs.

The startup is kicking off with a strong start: About 140 employees will move over to Cyclerion from Ironwood.