TSHA-102 in Rett syndrome heads toward BLA on a 100% response rate; the 6-month interim analysis will determine whether that signal is registrational

Bull

All 17 REVEAL patients demonstrate clinically meaningful and durable functional gains at the 6-month interim cut, and FDA confirms the interim dataset is sufficient to support a BLA submission — consistent with breakthrough therapy designation and prior Type B meeting alignment. This would allow Taysha to file the BLA materially earlier than the full 12-month timeline, compressing the path to potential approval and first commercial revenue, and cementing TSHA-102 as the leading gene therapy candidate in Rett syndrome on the strength of a clean safety record (zero treatment-related SAEs or DLTs across N=29) and broad patient coverage.

Bear

The most likely failure modes are FDA declining to accept the 6-month interim as sufficient for a complete BLA, requiring the full 12-month dataset and pushing out the filing timeline significantly, or the interim data showing that early functional gains are not sustained or are heterogeneous enough to raise questions about the primary endpoint's magnitude and durability. A MECP2-related adverse event — the class-level safety concern tied to MECP2 overexpression in gene therapy — emerging in any patient between the June 2026 data cut and the interim analysis would be a severe setback given the program's otherwise clean safety profile.