Ultragenyx: Short Sellers Dug In After GTX-102 Collapse

RARE heads into the post-earnings stretch carrying one of the highest short positions in its peer group, a wrecked pipeline narrative, and an analyst community that cannot agree on how low is low enough.

Short interest at 20.8% of the free float is the dominant feature of the positioning picture. That is up roughly 20% over the past month, a sharp acceleration that began around October 9 when shorts jumped from about 16.8 million shares to north of 20 million in a single session, a step-change that has since held almost perfectly flat. The borrow market remains strikingly benign given that volume of short interest: cost to borrow is running below 0.5% and availability is at approximately 1,296% of shares already borrowed, meaning lenders are sitting on roughly 91 million shares available against 20 million currently shorted. The lending pool is not under any pressure, and there is no mechanical squeeze dynamic in place. Options sentiment also leans bullish rather than defensive: the put/call ratio of 0.29 is near its 52-week low and fractionally below its 20-day average, suggesting options traders are not paying up for downside protection. The positioning picture, then, is an unusually clean one: a large short base, an easy borrow, and an options market that looks sanguine rather than alarmed.

The Street reflects the company's bifurcated reality. The bear case is blunt: the ASPIRE Phase 3 failure for GTX-102 eliminated what analysts had treated as the core long-term growth driver, wiping out $1.7 billion in projected peak revenue and forcing a reset of the breakeven timeline toward FY30. Goldman Sachs cut its target to $17 from $19 this week, landing just above the current price of $16.63. The bull case leans on the existing commercial base across Crysvita, Dojolvi, Mepsevii, and other franchises, plus a potential priority review voucher sale that could contribute roughly $400 million in non-dilutive capital. Most of the post-earnings analyst reaction on November 4 split that way: TD Cowen lifted its Buy target to $19, Morgan Stanley and Wells Fargo raised Equal-Weight targets to $22 and $19 respectively, while Wedbush cut to $22 on a Neutral and Goldman moved in the opposite direction. The mean consensus target of $26.35 looks stretched relative to a $16.63 price, reflecting targets set before or shortly after the GTX-102 failure that have not all been reset downward. The forward EPS percentile rank of 96 captures improving analyst estimates, but the negative PE and EV/EBITDA multiples confirm the company remains loss-making, and the earnings yield factor ranks in only the 25th percentile.

One ownership development worth flagging is the arrival of Madison Avenue International LP, which filed a fresh Schedule 13G on October 20 disclosing a 6.4% stake. The filing is passive, not activist, but at 6.3 million shares it makes Madison Avenue one of the five largest disclosed holders. BlackRock has also been building, filing a 13G/A in July showing 8.3% against 5.1% previously, and Vanguard Portfolio Management's most recent amendment in October shows 8.6%, up from 6.95%. There is no 13D activist on the register, and all of these moves are passive in character. As a caveat, 13D/G disclosures are event-driven around the 5% threshold, so the full current picture may differ from what is on file.

Retail attention has spiked sharply: ORTEX's Wikipedia and ORTEX page-view signal registered a z-score of 4.1 as of October 19, well above the stock's own 90-day baseline. That reading captures attention rather than any operational indicator, but it does suggest the GTX-102 failure and subsequent analyst coverage wave drove a meaningful wave of retail interest. Medicaid reimbursements for Ultragenyx drugs came in down 10% year on year in Q1 2026 based on CMS data, a number to hold alongside any discussion of the base business trajectory.

What to watch from here: the next earnings event is not until February 12, 2027, giving a 100-day window in which the debate will centre on whether the existing commercial franchises can grow fast enough to narrow losses and whether a PRV sale materialises, two data points that the current short base of 20.8% clearly doubts.