Ionis Pharmaceuticals has announced the completion of subject enrolment in the Phase I-III clinical trial evaluating Zilganersen (ION373) in individuals with Alexander disease (AxD).

An investigational RNA-targeted medicine, Zilganersen is designed to treat the rare neurological disorder affecting children and adults.

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The international, multicentre, randomised, double-blind, controlled, multiple-ascending dose trial enrolled participants aged two to 65 years across 13 sites in eight countries.

Patients were randomised into a 2:1 ratio to receive either Zilganersen or a control for a 60-week double-blind treatment period.

Following this phase, all participants will be treated with Zilganersen for a subsequent 180-week open-label treatment period, and then monitored for an additional 28 weeks post-treatment.

The percent variation from baseline in gait speed, measured by the 10-Meter Walk Test (10MWT) at the end of the double-blind treatment period is the trial’s primary endpoint.

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Secondary endpoints include changes from baseline in the Most Bothersome Symptom (MBS) Score, Patient Global Impression of Severity (PGIS) Score, Patient Global Impression of Change (PGIC) Score, and Clinician Global Impression of Change (CGIC) Score.

An open-label sub-study for eligible participants under two years of age with AxD will continue to accept enrolments until 2025.

Topline data from the trial are expected in the second half of 2025.

Ionis executive vice-president and chief clinical development officer Eugene Schneider said: “Current approaches to disease management for Alexander disease can mitigate some symptoms of AxD but do not address the underlying cause or slow disease progression. Our zilganersen study is the first trial to evaluate an investigational medicine designed to address the underlying cause of Alexander disease.

“We are grateful for the dedication and support from the patients, families and investigators in the Alexander disease community, whose partnership has made this milestone possible.”

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