Shares of Dimension Therapeutics Inc. (DMTX) rose 1.3% to $5.97 in morning trading on Tuesday, Oct. 3, after the company agreed to sell to Ultragenyx Pharmaceutical Inc. (RARE) - Get Report for $6 a share in cash or about $151 million.

Back in August, Dimension had agreed to sell to Regenxbio Inc. (RGNX) - Get Report in an all-stock deal for an implied value of about $3.41 per share. Then on Sept. 18, Ultragenyx made a bid to acquire Dimension for $5.50 per share, or about $138 million, in cash.

On Oct. 2, Dimension said Ultragenyx's unsolicited bid to buy Dimension for $6 a share constitutes a "superior proposal."

Ultragenyx shares were trading at $55.18 on Tuesday morning, down 3.7%. Regenxbio shares were changing hands at $33, down 1.5%.

Meanwhile, shares of Rigel Pharmaceuticals Inc. (RIGL) - Get Report were down 5.6% to $3.18 after rising 7% in premarket trading. The South San Francisco, Calif.-based firm said it had recently wrapped up enrollment of the first of its two-stage Phase 2 study of fostamatinib for the treatment of patients with warm antibody autoimmune hemolytic anemia (AIHA). Rigel said that on a topline, preliminary basis, the study met its primary efficacy endpoint for stage 1.

AIHA is a rare blood disorder in which the immune system produces antibodies that result in the destruction of the body's own red blood cells.

The announcement came a day after Rigel said the U.S. Food and Drug Administration had indicated that it does not plan to conduct an Oncology Drugs Advisory Committee meeting to discuss Rigel's new drug application for fostamatinib in chronic or persistent immune thrombocytopenia. The FDA also indicated that it anticipates meeting the Prescription Drug User Fee Act action date of April 17, 2018 for the application review, Rigel said.

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