FDA Approves Zanvastro for Alexander Disease After Trial Shows Stable Walking Speed Versus 33% Decline in Controls

Ionis Pharmaceuticals received FDA approval for Zanvastro in children and adults with Alexander disease, a rare leukodystrophy caused by GFAP mutations that previously lacked any targeted therapy. The decision rested on a randomized trial measuring 10-meter walk speed as the primary endpoint, with secondary signals of motor gains in younger patients and fewer serious adverse events in the treatment arm than controls.

The trial design mirrors antisense oligonucleotide successes in spinal muscular atrophy, where early intervention altered trajectories. Absolute stability versus a one-third functional loss provides clinically meaningful differentiation, though the study size remains modest given the disease's rarity and long-term durability data are still maturing.

Post-approval requirements will likely include a registry tracking real-world motor and cognitive outcomes across age groups. Expanded access for presymptomatic infants identified through newborn screening represents the next logical step if safety holds in the youngest cohorts.

Future studies need to link walking speed preservation to survival and quality-of-life metrics over five years while monitoring for off-target CNS effects.