Material Event (Form 8-K)

Item 8.01. Other Events.

On December 18, 2025, Gain Therapeutics, Inc. (the "Company") issued a press release announcing results in exploratory endpoint from its Phase 1b clinical study of GT-02287 in people with Parkinson's Disease ("PD"). All individuals with elevated levels of glucosylsphingosine ("GluSph") in the cerebrospinal fluid ("CSF") displayed large decreases back towards levels observed in healthy individuals after 90 days of treatment with GT-02287. The change observed in GluSph in CSF was a prespecified exploratory endpoint of this Phase 1b study. Part 1 (90 days of dosing) of the ongoing Phase 1b study has concluded. The Phase 1b study enrolled 21 participants, 19 completed the 90-day dosing period, and 15 (79%) chose to continue in the nine-month extension (Part 2) portion of the study that is anticipated to conclude in September 2026.

Consistent with the initial Phase 1b data presented at the International Congress of Parkinson's Disease and Movement Disorders in October 2025, GT-02287 continues to be generally well-tolerated over 90 days of dosing at plasma exposures within the projected therapeutic range. The data monitoring committee has recommended that the Phase 1b study continue with no changes.

Results from a Phase 1 study of GT-02287 in healthy volunteers demonstrated favorable safety and tolerability, plasma and central nervous system exposures in the projected therapeutic range, and target engagement with an increase in glucocerebrosidase ("GCase") activity among those receiving GT-02287 at clinically relevant doses.

GT-02287 is currently being evaluated in a Phase 1b clinical trial for the treatment of Parkinson's disease with or without a GBA1 mutation. The primary endpoint of the trial, which enrolled participants across seven sites in Australia, is to evaluate the safety and tolerability of GT-02287 after three months of dosing in people with PD. The Phase 1b study extension allows participants to continue to be treated with GT-02287 for up to a total of 12 months.

The Company also announced that it has a capital position to fund operations through the end of the Phase 1b extension and year-end 2026.