Material Agreement (Form 8-K)

On June 18, 2026, PTC Therapeutics, Inc. (the "Company") completed its previously announced private offering of $550,000,000 aggregate principal amount of its 0.0% Convertible Senior Notes due 2031 (the "Notes") and entered into an indenture with U.S. Bank Trust Company, National Association, as trustee (the "Trustee"), governing the Notes (the "Indenture"). The Notes were sold in a private placement under a purchase agreement, dated as of June 15, 2026, entered into by and between the Company and Morgan Stanley & Co. LLC, as representative of the several initial purchasers named in the purchase agreement (collectively, the "Initial Purchasers"), for resale to persons reasonably believed to be qualified institutional buyers pursuant to Rule 144A under the Securities Act of 1933, as amended (the "Securities Act"). The aggregate principal amount of the Notes sold reflects the exercise in full by the Initial Purchasers of their option to purchase up to an additional $50,000,000 in aggregate principal amount of the Notes.

The Notes will not bear regular interest, and the principal amount of the Notes will not accrete. The Notes may bear special interest under specified circumstances relating to the Company's failure to comply with its reporting obligations under the Indenture or if the Notes are not freely tradeable as required by the Indenture. Special interest, if any, will be payable semiannually in arrears on June 15 and December 15 of each year, beginning on December 15, 2026 (if and to the extent that special interest is payable). The Notes will mature on June 15, 2031, unless earlier converted, redeemed or repurchased pursuant to their terms.

The initial conversion rate of the Notes is 9.3042 shares of the Company's common stock, par value $0.001 per share (the "Common Stock"), per $1,000 principal amount of Notes (which is equivalent to an initial conversion price of approximately $107.48 per share). The conversion rate will be subject to adjustment upon the occurrence of certain specified events but will not be adjusted for any accrued and unpaid special interest. In addition, upon the occurrence of a make-whole fundamental change (as defined in the Indenture) or an issuance of a notice of redemption, the Company will, in certain circumstances, increase the conversion rate by a number of additional shares for a holder that elects to convert its Notes in connection with such make-whole fundamental change or notice of redemption.

Holders may convert all or any portion of their Notes at their option at any time prior to the close of business on the business day immediately preceding March 15, 2031 only under the following circumstances: (1) during any calendar quarter commencing after the calendar quarter ending on September 30, 2026 (and only during such calendar quarter), if the last reported sale price of the Common Stock for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter is greater than or equal to 130% of the conversion price on each applicable trading day; (2) during the five business day period after any five consecutive trading day period (the "measurement period") in which the trading price per $1,000 principal amount of Notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price of the Common Stock and the conversion rate on each such trading day; (3) if the Company calls any or all of the Notes for redemption, at any time prior to the close of business on the second scheduled trading day immediately preceding the relevant redemption date; or (4) upon the occurrence of specified corporate events. On or after March 15, 2031 until the close of business on the second scheduled trading day immediately preceding the maturity date, holders may convert all or any portion of their Notes at any time, regardless of the foregoing circumstances. Upon conversion, the Company will satisfy its conversion obligation by paying or delivering, as the case may be, cash, shares of Common Stock or a combination of cash and shares of Common Stock, at the Company's election.

The Company may not redeem the Notes prior to June 20, 2029. The Company may redeem for cash all or any portion of the Notes, at the Company's option, on or after June 20, 2029 if the last reported sale price of the Common Stock has been at least 130% of the conversion price then in effect for at least 20 trading days (whether or not consecutive) during any 30 consecutive trading day period (including the last trading day of such period) ending on, and including, the trading day immediately preceding the date on which the Company provides a written notice of redemption at a redemption price equal to 100% of the principal amount of the Notes to be redeemed, plus any accrued and unpaid special interest to, but excluding, the redemption date. No "sinking fund" is provided for the Notes.