POWER OF ATTORNEY

      Know all by these presents, that the undersigned hereby constitutes and
appoints each of Chris W. Trester and Yujin Yi of Gibson, Dunn & Crutcher LLP,
with full power of substitution, the undersigned's true and lawful attorney-in-
fact to:

      1.    execute for and on behalf of the undersigned, Forms 3, 4, and 5 in
            accordance with Section 16(a) of the Securities Exchange Act of 1934
            and the rules thereunder and Schedules 13D and 13G in accordance
            with Section 13 of the Securities Exchange Act of 1934 and the rules
            thereunder;

      2.    do and perform any and all acts for and on behalf of the undersigned
            which may be necessary or desirable to complete and execute any such
            Form 3, 4, or 5 or Schedules 13D or 13G, complete and execute any
            amendment or amendments thereto, and timely file such form with the
            SEC and any securities exchange or similar authority; and

      3.    take any other action of any type whatsoever in connection with the
            foregoing which, in the opinion of such attorney-in-fact, may be of
            benefit to, in the best interest of, or legally required by, the
            undersigned, it being understood that the documents executed by such
            attorney-in-fact on behalf of the undersigned pursuant to this Power
            of Attorney shall be in such form and shall contain such terms and
            conditions as such attorney-in-fact may approve in such attorney-in-
            fact's discretion.

      The undersigned hereby grants to such attorneys-in-fact full power and
authority to do and perform any and every act and thing whatsoever requisite,
necessary, or proper to be done in the exercise of any of the rights and powers
herein granted, as fully to all intents and purposes as the undersigned might or
could do if personally present, with full power of substitution or revocation,
hereby ratifying and confirming all that such attorney-in-fact, or such
attorney-in-fact's substitute or substitutes, shall lawfully do or cause to be
done by virtue of this power of attorney and the rights and powers herein
granted.  The undersigned acknowledges that the foregoing attorneys-in-fact, in
serving in such capacity at the request of the undersigned, are not assuming,
any of the undersigned's responsibilities to comply with the Securities Exchange
Act of 1934 or any rule or regulation of the SEC.

      This Power of Attorney shall remain in full force and effect until the (a)
the undersigned is no longer required to file Forms 3, 4, and 5 or Schedules 13D
or 13G with respect to the undersigned's holdings or (b) revocation by the
undersigned in a signed writing delivered to the foregoing attorneys-in-fact.

      IN WITNESS WHEREOF, the undersigned has caused this Power of Attorney to
be executed as of this 23 day of October, 2020.

                                       Fairmount Funds Management LLC
                                       Fairmount Healthcare Fund LP
                                       Fairmount Healthcare Fund II LP


                                       By:  /s/ Tomas Kiselak
                                            --------------------------------
                                       Name: Tomas Kiselak
                                       Title: Managing Member