On November 14, Boston-based Eventide Asset Management disclosed in a U.S. Securities and Exchange Commission filing that it sold 114,922 shares of Mirum (MIRM 1.85%). Nevertheless, the net position value actually increased by approximately $50.70 million.

What Happened

According to an SEC filing dated November 14, Eventide Asset Management, LLC reduced its stake in Mirum (MIRM 1.85%) by selling 114,922 shares since the previous quarter. The move brought the fund’s position to 2.52 million shares, or $184.92 million, as of September 30.

What Else to Know

Eventide sold shares, bringing Mirum to 3.04% of AUM and making it the fund’s second-largest equity holding. The position was previously about 2.4% of the fund's AUM as of the prior quarter.

Top holdings after the filing: 

• NASDAQ:GH: $207.51 million (3.4% of AUM)
• NASDAQ:MIRM: $184.92 million (3.0% of AUM)
• NASDAQ:XMTR: $169.87 million (2.8% of AUM)
• NYSE:TT: $168.00 million (2.8% of AUM)
• NASDAQ:INSM: $144.74 million (2.4% of AUM)

As of Friday, shares of Mirum were priced at $79.26, up a staggering 89% over the past year and well outperforming the S&P 500, which is instead up about 15%.

Company Overview

Company Snapshot

• Mirum's key products include LIVMARLI, an investigational oral therapy for rare liver diseases, and Volixibat, targeting additional rare hepatic conditions.
• The company generates revenue primarily through the development and commercialization of novel therapies for rare and orphan diseases, focusing on proprietary pharmaceutical products.
• Primary customers are healthcare providers and institutions treating patients with rare cholestatic liver diseases, including those with Alagille syndrome and progressive familial intrahepatic cholestasis.

Mirum is a biopharmaceutical company specializing in therapies for debilitating rare and orphan diseases, with a focus on liver disorders. The company leverages its expertise in drug development to address significant unmet medical needs, driving growth through proprietary product commercialization. Its strategic emphasis on rare disease markets provides a competitive edge by targeting high-value, underserved patient populations.

Foolish Take

For long-term investors, the most interesting signal here isn’t the share sale. It’s the willingness to let a position grow into one of the largest holdings in the portfolio while the stock is already up sharply. That tells you this isn’t about trading around short-term volatility. It’s about underwriting a business that is finally moving from promise to scale.

Mirum posted third-quarter revenue of $133 million (up 47%) and raised full-year guidance to $500 million to $510 million, driven by continued strength in LIVMARLI sales and expanding bile acid medicine revenue. Cash and investments climbed to $378 million by quarter end, giving the balance sheet room to fund multiple pipeline readouts without near-term dilution pressure. With this in mind, the share trim looks more like portfolio management than a loss of conviction, especially since the position’s value grew meaningfully thanks to price appreciation. Within the broader portfolio, this holding sits alongside other growth-oriented healthcare bets, reinforcing the idea that the manager is leaning into companies with clear commercial traction rather than binary clinical outcomes.

Glossary

Assets Under Management (AUM): The total market value of investments managed on behalf of clients by a fund or firm.
13F Reportable Assets: Securities that institutional investment managers must disclose quarterly to the SEC, as required by Form 13F filings.
Quarter-end: The last day of a fiscal quarter, often used as a reporting date for financial data.
Equity Position: Ownership in a company represented by shares held in an investment portfolio.
Orphan Disease: A rare medical condition affecting a small percentage of the population, often underserved by available treatments.
Proprietary Product: A product developed and owned exclusively by a company, often protected by patents or trade secrets.
Cholestatic Liver Disease: A condition where bile flow from the liver is reduced or blocked, leading to liver damage.
Unmet Medical Need: A health condition for which no adequate treatment exists, representing an opportunity for new therapies.
Quarterly Report: A financial statement released every three months detailing a company’s performance and position.
TTM: The 12-month period ending with the most recent quarterly report.
Biopharmaceutical Company: A firm that develops drugs using biological and chemical processes, often focusing on innovative therapies.
Commercialization: The process of bringing a new product or service to market and generating revenue from it.