Material Event Form 8 K

On October 17, 2024, Amylyx Pharmaceuticals, Inc. (the "Company") announced positive topline data from the Phase 2 open-label HELIOS clinical trial of AMX0035 (sodium phenylbutyrate [PB] and taurursodiol [TURSO, also known as ursodoxicoltaurine]) in 12 adults living with Wolfram syndrome. Wolfram syndrome is a rare, progressive, monogenic disease impacting approximately 3,000 people in the U.S. HELIOS showed improvement in pancreatic function, as measured by C-peptideresponse after 24 weeks of treatment with AMX0035, the study's primary efficacy endpoint, in contrast to the expected decrease in pancreatic function with disease progression. Similar overall improvements or stabilization were observed across all secondary endpoints, including hemoglobin A1c (HbA1c), time in target glucose range assessed by continuous glucose monitoring, and visual acuity. Patient- and physician-reported global impressions of change showed disease stability or improvement in all participants, meeting prespecified responder criteria. In addition, longer-term data for all participants who completed Week 36 (n=10) and Week 48 (n=6) assessments showed sustained improvement over time.

The analysis performed includes Week 24 data for all 12 participants and data for all participants who completed their Week 36 (n=10) and Week 48 (n=6) assessments as of the data cutoff.

HELIOS showed improvements in its primary endpoint of C-peptideresponse with a change from baseline to Week 24 at 120 minutes of +3.8 minutes*ng/mL (min*ng/mL) [standard error (SE): 19.3] in the Intent to Treat group (N=12) and +20.2 min*ng/mL [SE: 11.2] in the Per Protocol group (N=11). In addition, as outlined in the table below, participants receiving AMX0035 had improved glycemic control, as measured by markers of glucose metabolism; improved visual acuity in some participants, as measured by the Snellen chart; and improvement or stabilization of the disease, as measured by the Clinician Reported Global Impression of Change (CGIC) and Patient Reported Global Impression of Change (PGIC).

The safety profile of AMX0035 in HELIOS was consistent with prior safety data. AMX0035 was generally well-tolerated. All adverse events (AEs) were mild or moderate, and there were no serious AEs related to AMX0035 treatment. The most common AE was diarrhea.

Participants in HELIOS receive AMX0035 for up to 96 weeks followed by a four-week safety follow-up.Primary and secondary outcomes are assessed at Week 24 and at longer-term time points.

The U.S. Food and Drug Administration ("FDA") and the European Commission granted Orphan Drug Designation to AMX0035 for the treatment of Wolfram syndrome in November 2020 and August 2024, respectively. Amylyx plans to meet with the FDA and other stakeholders to inform a Phase 3 program and expects to provide an update in 2025.

Forward-Looking Statements

Statements contained in this Current Report on Form 8-Kregarding matters that are not historical facts are "forward-looking statements" within the meaning of the Private Securities Litigation Reform Act of 1995, as amended. Because such statements are subject to risks and uncertainties, actual results may differ materially from those expressed or implied by such forward-looking statements. Such statements include, but are not limited to, Amylyx' expectations regarding: the potential clinical benefit for AMX0035 to help people living with Wolfram syndrome; and interactions with regulatory authorities. Any forward-looking statements in this Current Report on Form 8-Kare based on management's current expectations of future events and are subject to a number of risks and uncertainties that could cause actual results to differ materially and adversely from those set forth in or implied by such forward-looking statements. Risks that contribute to the uncertain nature of the forward-looking statements include the risks and uncertainties set forth in Amylyx' United States Securities and Exchange Commission (SEC) filings, including Amylyx' Quarterly Report on Form 10-Qfor the quarter ended June 30, 2024, and subsequent filings with the SEC. All forward-looking statements contained in this Current Report on Form 8-Kspeak only as of the date on which they were made. Amylyx undertakes no obligation to update such statements to reflect events that occur or circumstances that exist after the date on which they were made.