| Explanation of Responses: |
| (1) | The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $8.40 to $9.39, inclusive. The reporting persons undertake to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares purchased at each separate price within the ranges set forth in footnotes (1), (4), (6), (8), (10) and (12) to this Form 4. |
| (2) | Represents (a) 1,146,325 shares of common stock held by Venrock Healthcare Capital Partners III, L.P. ("VHCP III"), (b) 114,532 shares of common stock held by VHCP Co-Investment Holdings III, LLC ("VHCP III Co"), (c) 530,137 shares of common stock held by Venrock Healthcare Capital Partners II, L.P. ("VHCP II"), and (d) 214,823 shares of common stock held by VHCP Co-Investment Holdings II, LLC ("VHCP II Co"). |
| (3) | VHCP Management III, LLC ("VHCPM III") is the sole general partner of VHCP III and the sole manager of VHCP III Co. VHCP Management II, LLC ("VHCPM II") is the sole general partner of VHCP II and the sole manager of VHCP II Co. Dr. Bong Koh and Nimish Shah are the voting members of VHCPM III and VHCPM II. Dr. Koh, Mr. Shah, VHCPM III and VHCPM II disclaim beneficial ownership over all shares held by VHCP III, VHCP III Co, VHCP II and VHCP II Co, except to the extent of their respective indirect pecuniary interests therein. |
| (4) | The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $9.40 to $10.00, inclusive. |
| (5) | Represents (a) 1,369,523 shares of common stock held by VHCP III, (b) 136,832 shares of common stock held by VHCP III Co, (c) 633,359 shares of common stock held by VHCP II, and (d) 256,650 shares of common stock held by VHCP II Co. |
| (6) | The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $6.63 to $7.62, inclusive. |
| (7) | Represents (a) 1,441,054 shares of common stock held by VHCP III, (b) 143,978 shares of common stock held by VHCP III Co, (c) 666,439 shares of common stock held by VHCP II, and (d) 270,055 shares of common stock held by VHCP II Co. |
| (8) | The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $7.63 to $8.05, inclusive. |
| (9) | Represents (a) 1,599,360 shares of common stock held by VHCP III, (b) 159,795 shares of common stock held by VHCP III Co, (c) 739,650 shares of common stock held by VHCP II, and (d) 299,721 shares of common stock held by VHCP II Co. |
| (10) | The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $7.61 to $8.60, inclusive. |
| (11) | Represents (a) 1,615,227 shares of common stock held by VHCP III, (b) 161,380 shares of common stock held by VHCP III Co, (c) 746,988 shares of common stock held by VHCP II, and (d) 302,694 shares of common stock held by VHCP II Co. |
| (12) | The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $8.61 to $9.00, inclusive. |
| (13) | Represents (a) 1,714,502 shares of common stock held by VHCP III, (b) 171,299 shares of common stock held by VHCP III Co, (c) 792,900 shares of common stock held by VHCP II, and (d) 321,299 shares of common stock held by VHCP II Co. |