F1Effective May 11, 2018, Frazier Healthcare V, L.P., distributed in-kind, without consideration, a total of 1,372,000 shares of Common Stock of the Issuer to its general and limited partners. The remaining securities are held by Frazier Healthcare V, L.P. Each of the Reporting Persons disclaims beneficial ownership of the shares except to the extent of their pecuniary interest therein, if any.

Remarks

This statement is filed by: (i) Frazier Healthcare V, L.P. ("Frazier Healthcare V"), Frazier Healthcare VII, L.P. ("Frazier Healthcare VII"), and Frazier Healthcare VII-A, L.P. ("Frazier Healthcare VII-A"), each a Delaware limited partnership and direct owners of the shares of Common Stock following the in-kind distribution of shares of the Issuer (together, the "Shares"); (ii) FHM V, L.P., a Delaware limited partnership and general partner to Frazier Healthcare V; FHM V, L.L.C. a Delaware limited liability company and general partner of FHM V, L.P.; FHM VII, L.P., a Delaware limited partnership and general partner to Frazier Healthcare VII and Frazier Healthcare VII-A; and FHM VII, L.L.C., a Delaware limited liability company and general partner of FHM VII, L.P.; and (iii) Alan Frazier, Nader Naini, Nathan Every and Patrick Heron, each of who are members of FHM V, L.L.C. and FHM VII, L.L.C. and may be deemed to share voting and investment power with respect to shares held by Frazier Healthcare V, Frazier Healthcare VII, and Frazier Healthcare VII-A. The Reporting Persons are jointly filing this Form 4 pursuant to Rule 16a-3(j) under the Exchange Act. Because no more than 10 reporting persons can file any one Form 4 through the Securities and Exchange Commission's EDGAR system, Frazier Healthcare V, FHM V, L.P., FHM V, L.L.C. and certain other affiliates of the Reporting Persons have filed a separate Form 4, in which the direct and indirect transactions of Frazier Healthcare V, FHM V, L.P., FHM V, L.L.C. are also reported, in addition to being reported on this Form 4.