At the 44th Annual J.P. Morgan Healthcare Conference in San Francisco, Biohaven's leadership addressed the complete response letter for their spinocerebellar ataxia program. The discussion covered regulatory process, study design, and internal FDA dynamics. But underneath all of that, the conversation kept circling back to what matters most: the patients.
According to StatPearls (National Library of Medicine), there are more than 40 identified genetic subtypes of SCA, with SCA3 (also known as Machado-Joseph disease) being the most common, making up 25-50% of cases. The global prevalence is estimated at 1-5 per 100,000 individuals. For those affected, the disease touches every part of daily life. Walking becomes uncertain, then impossible. Speech becomes slurred, then silent. And because SCA is autosomal dominant, each child of an affected parent has a 50% chance of inheriting the same mutation.
Biohaven CEO Vlad Coric mentioned that their data showed roughly a 70% slowing of disease progression with troriluzole (branded as VYGLXIA). That is not a cure, but it can mean more time with coordination, more time with speech, and more time with independence. In conditions like this, time really matters.
Why the FDA Rejected Biohaven's SCA Treatment
What stood out was how Coric described the issue behind the complete response letter. It was not about safety or suddenly finding something wrong with the data. The CRL, issued on November 4, 2025, centered on the FDA's concerns about Biohaven's use of real-world evidence and externally controlled studies, citing potential bias, design flaws, and unmeasured confounding factors.
But as Coric pointed out, Biohaven ended up in a gray area of regulatory inconsistency. Different divisions within the FDA apply different standards for rare diseases. Some groups are willing to accept smaller or less traditional evidence packages when treatment options are limited, while others apply a bar that looks more like what you would expect for common diseases with large patient populations and straightforward trial designs.
This is harder to reconcile when Congress has been clear about encouraging maximum regulatory flexibility for rare and life-threatening conditions. The National Ataxia Foundation surveyed more than 3,000 members of the ataxia community after the CRL, and 97% said the FDA should apply regulatory flexibility and accept the application for full review.
8 Years of SCA Clinical Development
This program was not rushed. Biohaven worked with the FDA for roughly 8 years with ongoing feedback and oversight. The troriluzole clinical development program was the first in the industry to generate data showing therapeutic potential in SCA patients. It met its primary endpoint on the functional Scale for the Assessment and Rating of Ataxia (f-SARA) and showed statistically significant results across 9 consecutive, prespecified primary and secondary endpoints at the 3-year mark.
Over timelines like that, administrations change, review teams evolve, and internal priorities shift. Even when the science stays consistent, the measuring stick can move. That makes rare disease development even harder, especially when there are no alternative treatments and the disease keeps progressing.
The financial fallout was significant. Following the CRL, Biohaven announced it cut R&D spending by 60% and restructured around a leaner operating model. For a company that spent nearly a decade building this program, the regulatory setback carried real consequences beyond the science.
A Pattern Across Rare Disease FDA Decisions
This pattern is not unique to Biohaven. Similar challenges played out recently at Atara Biotherapeutics, where the FDA issued a second complete response letter for tabelecleucel (Ebvallo) in January 2026 for EBV-positive post-transplant lymphoproliferative disease. In that case, the FDA reversed course on a trial design it had previously confirmed as adequate to support the application. That condition affects roughly 500 patients per year in the U.S., and leaves them with weeks or months to live.
These decisions affect more than timelines or valuations. They shape whether patients ever gain access to therapies that may slow decline or extend life. These companies are not talking about common diseases or cosmetic treatments. For some patients, this is life or death.
“Days matter.”
Biohaven, on the urgency of SCA treatment
What Comes Next for Troriluzole and SCA Patients
To Biohaven's credit, the company has stayed forward-looking. They continue to advocate for SCA patients and have requested a Type A meeting with the FDA to clarify the path forward for troriluzole. The fight for approval is far from over.
Meanwhile, the rest of Biohaven's portfolio continues to advance. The early data from their degrader platform are genuinely exciting. At J.P. Morgan, the company shared early clinical results from their MoDE and TRAP degrader programs, including rapid and selective removal of disease-causing proteins with early clinical improvement in patients.
Their BHV-1300 MoDE degrader showed complete suppression of disease-causing antibodies in a Graves' disease patient within weeks. And BHV-1400 achieved selective lowering of the disease-causing protein in IgA nephropathy, with resolution of blood in the urine and improvement in kidney function. Both programs are moving toward pivotal studies in 2026.
It is encouraging to see real innovation continue to move forward, even when one path becomes uncertain.
Understanding [Spinocerebellar Ataxia](/trials/spinocerebellar-ataxia)
For patients and caregivers looking to learn more
SCA is a group of inherited neurodegenerative disorders caused by genetic mutations, most commonly CAG repeat expansions, that progressively damage the cerebellum. The cerebellum is the part of the brain responsible for coordinating movement, balance, and speech.
The most common subtypes include SCA3 (25-50% of cases), SCA2 (13-18%), SCA6 (13-15%), and SCA7. Symptoms typically begin in adulthood and worsen over time: progressive loss of balance and coordination (ataxia), slurred speech (dysarthria), difficulty swallowing (dysphagia), involuntary eye movements, and in many subtypes, cognitive and mood changes.
There are currently no FDA-approved disease-modifying treatments for any form of SCA. Management is limited to physical therapy, occupational therapy, speech therapy, and assistive devices. That is what makes the pursuit of treatments like troriluzole so critical for this community.