Avexis Inc. (AVXS): RA Capital Management Ups Its Stake

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

Under the Securities Exchange Act of
1934

(Amendment No. __)*

AveXis, Inc.

(Name of Issuer)

Common Stock, par value $0.0001 per share

(Title of Class of Securities)

05366U100

(CUSIP Number)

December 14, 2016

(Date of Event Which Requires Filing of
this Statement)

Check the appropriate box to designate the rule pursuant to
which this Schedule is filed:

*The remainder of this cover page shall
be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for
any subsequent amendment containing information which would alter the disclosures provided in a prior cover page.

The information required in the remainder
of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of
1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject
to all other provisions of the Act (however, see the Notes).

¹
The reporting person is the beneficial owner of 1,890,796 shares of the Issuer’s Common Stock which constitute approximately
6.8% of the Issuer’s outstanding Common Stock shares. The percentage calculation assumes that there are currently 27,676,288
outstanding shares of Common Stock of the Issuer, based on the Issuer’s Form 10-Q as filed with the Securities and Exchange
Commission (“SEC”) on November 10, 2016.

¹
The reporting person is the beneficial owner of 1,890,796 shares of the Issuer’s Common Stock which constitute
approximately 6.8% of the Issuer’s outstanding Common Stock shares. The percentage calculation assumes that there are currently
27,676,288 outstanding shares of Common Stock of the Issuer, based on the Issuer’s Form 10-Q as filed with the Securities
and Exchange Commission (“SEC”) on November 10, 2016.

¹
The reporting person is the beneficial owner of 1,476,084 shares of the Issuer’s Common Stock which constitute
approximately 5.3% of the Issuer’s outstanding Common Stock shares. The percentage calculation assumes that there are currently
27,676,288 outstanding shares of Common Stock of the Issuer, based on the Issuer’s Form 10-Q as filed with the Securities
and Exchange Commission (“SEC”) on November 10, 2016.

Item 1.

(a)       Name
of Issuer: AveXis, Inc. (the “Issuer”).

(b)       Address of the
Issuer’s Principal Executive Offices: 2275 Half Day Road, Suite 160, Bannockburn,
IL 60015.

Item 2.

(a)       Name
of Person Filing: This joint statement on Schedule 13G is being filed by RA Capital Management, LLC (“Capital”),
Peter Kolchinsky and RA Capital Healthcare Fund, L.P. (the “Fund”). Capital, Mr. Kolchinsky and the Fund are collectively
referred to herein as the “Reporting Persons.” Capital is the general partner of the Fund and serves as investment
adviser for a separately managed account (the “Account”). Mr. Kolchinsky is the manager of Capital. As the investment
adviser to the Fund and the Account, Capital may be deemed a beneficial owner, for purposes of Section 13(d) of the Securities
Exchange Act of 1934 (the “Act”), of any securities of the Issuer owned by the Fund or the Account. As the manager
of Capital, Mr. Kolchinsky may be deemed a beneficial owner, for purposes of Section 13(d) of the Act, of any securities of the
Issuer beneficially owned by Capital. Capital is a registered investment adviser within the meaning of Rule 13d-1(b)(1)(ii)(E)
and Rule 16a-1(a)(v), and Mr. Kolchinsky is a parent or control person of Capital within the meaning of Rule 13d-1(b)(1)(ii)(G)
and Rule 16a-1(a)(1)(vii). Capital and Mr. Kolchinsky disclaim beneficial ownership of the securities reported in this Schedule
13G Statement (the “Statement”) other than for the purpose of determining their obligations under Section 13(d) of
the Act, and the filing of the Statement shall not be deemed an admission that either Capital or Mr. Kolchinsky is or was the beneficial
owner of such securities for any other purpose.

(b)       Address
of Principal Business Office: The principal business office of the Reporting Persons is c/o RA Capital Management, LLC, 20
Park Plaza, Suite 1200, Boston, MA 02116.

(c)        Citizenship:
Capital is a Massachusetts limited liability company. The Fund is a Delaware limited partnership. Mr. Kolchinsky is a United States
citizen.

(d)       Title
and Class of Securities: Common stock (“Common Stock”) of the Issuer.

(e)       CUSIP
Number: 05366U100

Item 3. If this statement is filed
pursuant to §§240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:

Not applicable.

Item 4. Ownership:

Item 5. Ownership of Five Percent
or Less of a Class:

Not applicable.

Item 6. Ownership
of More than Five Percent on Behalf of Another Person:

Not applicable.

Item 7. Identification and Classification
of the Subsidiary Which Acquired the Security Being Reported on By the Parent Holding Company or Control Person:

Not applicable.

Item 8. Identification and Classification
of Members of the Group:

Not applicable.

Item 9. Notice of Dissolution of
Group:

Not applicable.

Item 10. Certification:

By signing below I hereby certify that,
to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of
or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held
in connection with or as a participant in any transaction having that purpose or effect.

SIGNATURE

After reasonable inquiry
and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Date: December
23, 2016

RA CAPITAL MANAGEMENT, LLC

By: /s/ Rajeev Shah

————————————————-

Rajeev Shah

Authorized Signatory

PETER KOLCHINSKY

/s/ Peter Kolchinsky

————————————————-

RA CAPITAL HEALTHCARE FUND, L.P.

By: RA Capital Management, LLC

Its: General Partner

By: /s/ Rajeev Shah

————————————————-

Rajeev Shah

Authorized Signatory