Spark Therapeutics (ONCE) 10-Q 2016 Q3 Quarterly report

Exhibit 32.1

CERTIFICATION PURSUANT TO 18 U.S.C. SECTION 1350,

AS ADOPTED PURSUANT TO

SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

In connection with the Quarterly Report on Form 10-Q of Spark Therapeutics, Inc. (the “Company”) for the period ended September 30, 2016 as filed with the Securities and Exchange Commission on the date hereof (the “Report”), I, Jeffrey D. Marrazzo, Chief Executive Officer of the Company, hereby certify, pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that to my knowledge:

(1) the Report fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

(2) the information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

Date: November 4, 2016	By:	/s/ Jeffrey D. Marrazzo
		Jeffrey D. Marrazzo
		Chief Executive Officer
		(Principal Executive Officer)