On microdystrophin, the FDA is doing what the accelerated-approval standard has always required: asking that a biomarker be shown to predict real benefit before it is trusted.
Much of the commentary around REGENXBIO’s RGX-202 has framed the FDA’s stance as regulatory inconsistency, arguing that the agency is holding one sponsor to a standard it waived for another. But the question before the FDA is simpler: whether microdystrophin expression is actually strong enough to predict clinical benefit.
The charge of inconsistency does not survive contact with the record. And it is worth noticing that its loudest version comes from a sponsor whose commercial position gives it every reason to want the bar set lower.
Nor is REGENXBIO alone in having a commercial interest in how low that bar is set. Solid Biosciences is pursuing the same accelerated-approval opening for SGT-003 while emphasizing high microdystrophin expression and other biomarker results from its early-stage trial. Solid is still gathering the controlled functional evidence that can show whether those laboratory findings actually translate into meaningful improvement for boys with Duchenne. That is precisely why the FDA cannot allow impressive protein numbers themselves to become the standard of proof.
The problem is larger than any one company. If microdystrophin expression can secure accelerated approval without convincing evidence that it predicts how patients actually function, every sponsor developing a similar therapy has an incentive to race toward the biomarker rather than wait for the harder clinical answer.
