X0206 3 2018-12-19 1 0001609727 Synthorx, Inc. THOR 0001304113 Powell Andrew Kenneth William C/O SYNTHORX, INC. 11099 N. TORREY PINES ROAD, SUITE 190 LA JOLLA CA 92037 1 0 0 0 No securities are beneficially owned. /s/ Christian V. Kuhlen, Attorney-in-Fact 2018-12-21