Mirum Pharmaceuticals shares are lower today as traders focus on new insider-selling related disclosures. The company’s SEC filing calendar shows a Rule 144 notice dated April 15, 2026, followed by an insider Form 4 filed April 16, 2026, which can often trigger short-term selling pressure as markets anticipate incremental share supply. (marketbeat.com)

Mirum has had an active equity-supply backdrop in early 2026, including a registration statement/prospectus materials that register up to 8,960,998 shares of common stock for potential resale by selling stockholders. Even when a filing is for resale (not a new primary issuance by the company), the market can treat it as an overhang because it expands the pool of shares that may be sold into the open market. (d18rn0p25nwr6d.cloudfront.net)

Key near-term signals are whether trading volume expands, whether additional Form 144s or Form 4s appear, and whether investors see follow-through selling tied to the registered resale shares. Any company updates on commercialization performance or pipeline milestones could also quickly overwhelm the technical selling narrative and reverse the move.