THOR Synthorx Inc

FORM 4 [X] Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).         
UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES                                                                                   
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Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940                       

1. Name and Address of Reporting Person * Avalon Ventures X, L.P.	2. Issuer Name and Ticker or Trading Symbol Synthorx, Inc. [ THOR ]	5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director                    __X__ 10% Owner _____ Officer (give title below)    _____ Other (specify below)
(Last)          (First)          (Middle) 11099 N. TORREY PINES ROAD, SUITE 290	3. Date of Earliest Transaction (MM/DD/YYYY) 1/14/2020
(Street) LA JOLLA, CA 92037 (City)        (State)        (Zip)	4. If Amendment, Date Original Filed (MM/DD/YYYY)	6. Individual or Joint/Group Filing (Check Applicable Line) ___ Form filed by One Reporting Person _ X _ Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1.Title of Security (Instr. 3)	2. Trans. Date	2A. Deemed Execution Date, if any	3. Trans. Code (Instr. 8)		4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Stock	1/14/2020		J(1)		4598796	D	(1)	150000	D (2)
Common Stock								1682086	I (2)	By Avalon X SPV I, L.P.

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivate Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Trans. Date	3A. Deemed Execution Date, if any	4. Trans. Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares

Explanation of Responses:
(1)	These shares were distributed on a pro rata basis to the partners of Avalon Ventures X, L.P. without the receipt of consideration.
(2)	Avalon Ventures X GP LLC ("Avalon X GP") and Avalon Ventures X SPV GP LLC ("Avalon X SPV GP") are general partners of Avalon Ventures X, L.P. ("Avalon Ventures") and Avalon X SPV I, L.P. ("Avalon SPV") and may be deemed to have voting and investment power with respect to the shares held by Avalon Ventures and Avalon SPV and as a result may be deemed to have beneficial ownership of such shares.

Reporting Owners
Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
Avalon Ventures X, L.P. 11099 N. TORREY PINES ROAD, SUITE 290 LA JOLLA, CA 92037		X
Avalon X SPV, L.P. 11099 N. TORREY PINES ROAD, SUITE 290 LA JOLLA, CA 92037		X

Signatures
/s/ Jay Lichter, Authorized Signatory for Avalon Ventures X, L.P.		1/16/2020
**Signature of Reporting Person		Date
/s/ Jay Lichter, Authorized Signatory for Avalon X SPV I, L.P.		1/16/2020
**Signature of Reporting Person		Date