Material Event (Form 8-K)

Item 8.01 Other Information

On October 6, 2025, Gain Therapeutics, Inc. (the "Company") presented preliminary data from the Company's ongoing Phase 1b clinical study of GT-02287 in people with Parkinson's disease ("PD") with or without a GBA1 mutation at the International Congress of Parkinson's Disease and Movement Disorders.

Preliminary Findings

After 90 days of dosing, GT-02287 has been safe and generally well tolerated, with no treatment-emergent serious adverse events observed. A transient increase in alkaline phosphatase and other liver enzymes has been observed in some participants and normalized despite ongoing dosing. Of the 21 study participants, two are treatment-naïve, two are on deep brain stimulation, and 18 are on levodopa and/or dopamine agonists or other PD drugs.

Mean MDS-UPDRS scores at baseline were 5.8, 7.4, and 24.7 for Parts I, II, and III, respectively. Several participants experienced an improvement in their UPDRS Part II and III scores after 90 days of dosing with GT-02287 while mean Part I scores remained unchanged. The mean improvement in Parts II and III by Day 90, which was not observed by Day 30, suggests that GT-02287 has a disease-slowing effect, consistent with the preclinical models in vivo and the proposed mechanism of action of GT-02287, supporting continued development. The plasma pharmacokinetics (PK) profile was consistent across all 14 participants sampled, was within the projected therapeutics range, and comparable to exposures observed in healthy volunteers in the Phase 1 study.

At two different meetings, the data monitoring committee has recommended continuation of the study and more recently, Australian health authorities have approved the Phase 1b study extension for patients who can now be treated for up to 12 months.