UCB presents positive results for fenfluramine in CDKL5 deficiency disorder
Esme Needham | December 8, 2025 | News story | Research and Development | Neurology, UCB, epilepsy
UCB has announced positive results from its phase 3 GEMZ study, showing that fenfluramine can significantly reduce the frequency of countable motor seizures in CDKL5 deficiency disorder (CDD).
CDD is a rare developmental and epileptic encephalopathy (DEE) characterised by severe global neurodevelopmental delays, multiple types of drug-resistant seizures, and impairments in sleep, gastrointestinal and intellectual function. It is caused by pathogenic variants in the cyclin dependent kinase-like 5 (CDKL5) gene, and affects around one in every 40,000-60,000 live births.
The GEMZ study found significant reduction in seizure frequency among patients treated with fenfluramine. Patients receiving the drug achieved a median reduction in countable motor seizure frequency (CMSF) of 47.6% from baseline, with 45.2% of treated patients achieving at least a 50% reduction by week 14 of the study. Caregivers of treated patients, as well as the study’s researchers, reported significant improvements.
Fenfluramine was found to be generally well tolerated, with no new safety signals being identified. Fenfluramine is already approved in the European Union, US and Japan for the treatment of Dravet syndrome and Lennox-Gastaut syndrome, and in CDD it demonstrated a safety profile consistent with its indications in these conditions.
Fiona du Monceau, executive vice president of patient evidence at UCB, said: “Families affected by this ultra-rare condition face immense daily challenges with frequent, treatment-resistant seizures that are profoundly disruptive to daily life. These trial results emphasise the impact that seizure control can have on the lives of patients and their families.” Du Monceau also noted UCB’s plans to work with health authorities in order for fenfluramine to be approved as a treatment for CDD.
UCB focuses on the discovery and development of new medicines across a range of therapeutic areas.
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