Sionna Therapeutics has drawn investor investigations from Robbins Geller Rudman & Dowd LLP and Levi & Korsinsky after the clinical-stage biopharmaceutical company disclosed on Aug. 10, 2026 that its Phase 2a PreciSION CF trial of SION-719 failed to meet a key activity endpoint for sweat chloride reduction when added to standard of care. Levi & Korsinsky said the one-session selloff erased about 92% of Sionna's market value, while other materials described the stock as falling roughly 90% from the mid-$40s to about $4 a share after the company reported a placebo-adjusted sweat chloride change of -1.0 mmol/L with a p-value of 0.7 and said it would not advance SION-719 as an add-on therapy. The trading shock came despite Sionna reporting about $268.3 million in cash, cash equivalents and marketable securities as of June 30, 2026, a second-quarter net loss of $29.9 million and a stated cash runway into 2028. The firms are seeking information from investors who bought Sionna securities before the disclosure and suffered losses.