Rare-Disease Biotech PTC Is Surging — And One Fund Just Raised Its Bet. Should You?

San Diego-based Tang Capital Management reported a $38.3 million increase in its stake in PTC Therapeutics (NASDAQ:PTCT) as of September 30, according to its latest SEC filing.

What Happened

Tang Capital disclosed in its November 14 Form 13-F filing that it increased its position in PTC Therapeutics(NASDAQ:PTCT) by 400,000 shares over the prior quarter. The fund’s holding rose to 1.5 million shares with a reported value of $92.1 million as of September 30. The quarter’s net position change in PTCT was $38.3 million.

What Else to Know

The buy helped raise PTCT to 3.5% of Tang's nearly $2.6 billion in reportable U.S. equity AUM, making it the fund’s fourth-largest holding.

Top holdings after the filing:

• NASDAQ: TARS: $145.9 million (5.6% of AUM)
• NASDAQ: GLPG: $143.8 million (5.5% of AUM)
• NASDAQ: AUPH: $125.2 million (4.8% of AUM)
• NASDAQ: PTCT: $92.1 million (3.5% of AUM)
• NASDAQ: MIRM: $90.6 million (3.5% of AUM)

As of Tuesday, shares of PTC Therapeutics were priced at $78.50, up 51% over the prior year and well outperforming the S&P 500, which is up 13% in the same period.

Company Overview

Company Snapshot

• PTC Therapeutics commercializes rare disease therapies, including Translarna, Emflaza, Tegsedi, Waylivra, and Evrysdi, with a pipeline spanning clinical to pre-clinical stages focused on neuromuscular and genetic disorders.
• The company generates revenue primarily through the sale and licensing of proprietary pharmaceutical products and strategic collaborations with industry partners.
• It serves patients with rare and orphan diseases, targeting healthcare providers, specialty pharmacies, and government agencies across North America, Europe, Latin America, and select international markets.

PTC Therapeutics, Inc. is a mid-cap biopharmaceutical company specializing in the development and commercialization of innovative therapies for rare genetic disorders. The company leverages a diversified portfolio of approved products and a robust pipeline to address unmet medical needs in the rare disease space. Its strategic collaborations and global reach position it as a key player in the biotechnology sector focused on rare diseases.

Foolish Take

This latest move into PTC Therapeutics comes at a moment when the company is showing real commercial momentum—not just pipeline promise. The launch of Sephience is off to a strong start, and PTC has swung into profitability, giving investors fresh visibility into a business that has historically been volatile. For a stock sitting near all-time highs after major swings over the last decade, that combination of sustained growth and improving fundamentals is meaningful.

According to a November 14 SEC filing, Tang Capital Management raised its position in PTC Therapeutics by 400,000 shares in the third quarter, boosting the value of its stake by $38.3 million. The fund now owns 1.5 million shares valued at $92.1 million, representing 3.5% of its nearly $2.6 billion reportable U.S. equity portfolio. That increase aligns with PTC’s accelerating fundamentals: Revenue climbed to $211 million in the third quarter, driven by $19.6 million in Sephience launch revenue and a surge in royalty income tied to Evrysdi. The company also swung to a quarterly net profit of $15.9 million, compared with a $106.7 million loss a year earlier.

The takeaway here is that PTC’s growth is broadening, not relying solely on one franchise. Still, the stock’s extreme volatility—and a pipeline with regulatory risk—means any position should be sized with care.

Glossary

Stake: The ownership interest or investment a fund or individual holds in a company.
Form 13-F: A quarterly SEC filing by institutional investment managers disclosing their equity holdings.
AUM (Assets Under Management): The total market value of investments managed by a fund or investment firm.
Reportable U.S. equity AUM: The portion of a fund’s assets invested in U.S. stocks that must be disclosed to regulators.
Quarter over quarter: A comparison of financial or investment data from one fiscal quarter to the next.
Holding: The amount of a particular security owned by an investor or fund.
Outperforming: Achieving a higher return or better performance than a benchmark or index.
Mid-cap: Refers to companies with a medium-sized market capitalization, typically between $2 billion and $10 billion.
Rare disease therapies: Treatments developed for diseases affecting a small percentage of the population, often called orphan diseases.
Pipeline: The set of drug candidates a pharmaceutical company is developing, from pre-clinical to clinical stages.
Strategic collaborations: Partnerships between companies to jointly develop, market, or distribute products or technologies.
TTM: The 12-month period ending with the most recent quarterly report.

Jonathan Ponciano has no position in any of the stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.