Third Rock Ventures LLC, a venture capital firm with offices in Boston and San Francisco, announced Thursday the formation of Global Blood Therapeutics Inc. and its $40.7 million Series A financing.

Global Blood Therapeutics is building a pipeline of medicines for severe genetic blood diseases. The company’s lead program focuses on sickle cell disease.

Global Blood Therapeutics marks the first company formation and launch out of Third Rock Ventures’ West Coast office, the firm said.

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Mark A. Goldsmith, a medical doctor with a Ph.D., is the firm’s chief executive. He is also a venture partner at Third Rock.