FDA Approves First Drug for Rare Neurodevelopmental Disorder Rett Syndrome

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Treatment with trofinetide (DAYBUE) demonstrated statistically significant improvement in the phase 3 LAVENDER study evaluating the drug's safety and efficacy.

The US Food and Drug Administration (FDA) approved trofinetide (DAYBUE) for the treatment of Rett syndrome in both adult and pediatric patients aged 2 years and older. This decision marks the first and only FDA approval of a drug for the rare neurodevelopmental disorder.

Individuals with Rett syndrome have a specific genetic mutation which causes developmental regression, including the loss of communication skills and purposeful hand use, as well as hand stereotypies and gait abnormalities. The number of Rett syndrome diagnoses is estimated to be around 4500 patients in the US, but the amount of patients impacted by the disorder is thought to be between 6000 to 9000.

“Rett syndrome is a profoundly debilitating and complex, rare, neurodevelopmental disorder that presents differently across patients and can lead to an array of unpredictable symptoms throughout the course of a patient’s life,” Jeffrey L. Neul, MD, PhD, LAVENDER study investigator and director of Vanderbilt Kennedy Center, Professor of Pediatrics, Division of Neurology, Pharmacology, and Special Education, Vanderbilt University Medical Center said in a statement.

The efficacy and safety of trofinetide were evaluated in the pivotal phase 3 LAVENDER study, which involved 187 female patients aged 5-20 years. The study demonstrated that treatment with trofinetide showed statistically significant improvement when compared with placebo.

These results fulfilled both co-primary efficacy endpoints, as measured by the change in Rett Syndrome Behaviour Questionnaire (RSBQ) total score and the Clinical Global Impression-Improvement (CGI-I) scale score at week 12.

The most common side effects of trofinetide were diarrhea and vomiting, according to the study.

According to developing company Acadia Pharmaceuticals, trofinetide is expected to be available to patients in the US by the end of April 2023. In 2018, Acadia had entered into an exclusive license agreement with Neuren Pharmaceuticals Limited (ASX: NEU) to develop and commercialize trofinetide for the treatment of Rett syndrome and other potential indications in North America.

As a result of the FDA's approval of trofinetide, Acadia has received a Rare Pediatric Disease Priority Review Voucher, which can be utilized to obtain priority review for a subsequent application.

“Now, for the first time after decades of clinical research, healthcare providers finally have a treatment option to address a range of core behavioral, communication and physical symptoms for their patients living with Rett syndrome,” Neul stated.


  1. Acadia Pharmaceuticals Announces U.S. FDA Approval of DAYBUE™ (trofinetide) for the Treatment of Rett Syndrome in Adult and Pediatric Patients Two Years of Age and Older. Acadia Pharmaceuticals. Published March 10, 2023. Accessed March 13, 2023.