Neuren Pharmaceuticals (ASX: NEU) has begun dosing in the Koala Phase 3 trial of NNZ-2591 for Phelan-McDermid syndrome. The first child completed screening and started the 13-week, twice-daily regimen. It is the first Phase 3 study ever conducted in this rare genetic condition. No approved therapies currently exist for the disorder.
Koala is a randomized, double-blind, placebo-controlled study targeting about 160 children aged three to twelve. After a screening window of up to four weeks, participants receive NNZ-2591 or placebo for 13 weeks. Safety and efficacy endpoints will guide potential regulatory filings in the US.
Strong Early Demand From Families
Recruitment signals are encouraging. Twenty-five families have already been referred to the initial two trial sites. Another 37 families sit on waitlists for locations closer to home. Two additional sites are expected to activate this month. A further 20 US centers are progressing toward activation during the first half of the year.
Neuren is also sponsoring the 2026 Phelan-McDermid Syndrome Foundation Family Conference in Colorado. The event will take place in July and aims to support education and community engagement.
Chief executive Jon Pilcher said: “We are excited to have started the treatment phase of our Koala Phase 3 study and are very encouraged by the level of interest in the PMS community. We are proud to be the presenting sponsor of the PMSF Family Conference in July and we anticipate strong momentum for Koala as trial sites around the US progressively activate during the first half of this year.”
Why This Program Stands Out
NNZ-2591 carries three key FDA designations: Fast Track, Rare Pediatric Disease and Orphan Drug. Receiving all three for one program is uncommon in neurology and signals high unmet need. Fast Track allows more frequent engagement with regulators and a potential accelerated review. Orphan Drug status offers market exclusivity and fee reductions. Rare Pediatric Disease designation may deliver a priority review voucher if the drug is approved.
About Phelan-McDermid Syndrome
Phelan-McDermid syndrome, often called PMS or 22q13 deletion syndrome, results from disruption of the SHANK3 gene. The condition affects synaptic function in the brain. It is estimated to occur in roughly one in 8,000 to one in 15,000 people in the United States. Symptoms include intellectual impairment, absent speech, autism features and epilepsy. Families face lifelong care needs and few treatment options.
Commercial Context
Neuren already markets trofinetide for Rett syndrome through partner Acadia Pharmaceuticals. Success with NNZ-2591 would expand the company into a second rare pediatric franchise. The Koala trial builds on positive Phase 2 data across three disorders. Investors will watch enrollment pace and interim safety closely over 2026.
What Comes Next?
More participants are scheduled to begin dosing through February and March. Site activation remains the key variable for timelines. Data from Koala could position NNZ-2591 as the first approved therapy for PMS.
