What is being worked on, described by how it is intended to act rather than by how promising anyone says it is.
How this got here
Worth seeing laid out, because it shows how recent all of it is. The first SCA gene was only found in the 1990s, and the first industry trial programme in this condition is younger than most of the people reading this.
1863
The first description
Nikolaus Friedreich describes an inherited, progressive ataxia. For more than a century afterwards, these conditions can be observed and named but not explained.
1993
The first SCA gene is found
The gene behind SCA1 is identified, and with it the repeat expansion mechanism. For the first time the cause is a specific, countable thing rather than a family pattern.
1990s–2000s
The types are sorted out
One gene after another: SCA2, SCA3, SCA6, SCA7 and more. "Hereditary ataxia" becomes dozens of separately named conditions, each with a genetic test.
2023
SCA27B is described
A repeat expansion in FGF14 turns out to explain a substantial share of late-onset ataxia that had gone unexplained for decades. People who had been told there was no answer suddenly have one.
Listed alphabetically. The order carries no judgement, and we make no comparisons between them. This covers programmes we could document from a registry record, a regulatory announcement or a company filing; the live trials page will show studies not listed here.
Status unclearSmall molecule
SLX-100
Solaxa, with Alvogen under a global licensing agreement
How it is intended to work
An investigational therapy directed specifically at SCA27B, the FGF14-related form of the condition.
Aimed at one specific genetic type rather than the ataxias as a group — an example of treatments being designed around a single gene.
Where it stands
Announced; stage not independently confirmed
The National Ataxia Foundation has reported a licensing agreement to advance this programme. We have not found a registered trial record we can point you to, so treat the development stage as unconfirmed and check the foundation’s pharma news page for updates.
Trehalose, a sugar that has been studied for its effects on the cellular pathways that clear away damaged or misfolded proteins.
The idea being tested was whether helping cells dispose of protein waste more efficiently changes the course of the disease.
Where it stands
Phase 2b/3 study completed in November 2023
The STRIDES study was a randomised, double-blind, placebo-controlled trial in adults with SCA. The registry record lists an actual completion date of 24 November 2023. Completion of a study means the study finished, not that the treatment worked or that it is available. Check the registry record and the sponsor for reported results.
A third-generation prodrug of riluzole that modulates glutamate, an excitatory chemical messenger. It is intended to increase glutamate uptake out of the synapse by acting on transporters on glial cells.
Glutamate is a signal that nerve cells use to excite one another. Too much of it lingering in the wrong place is thought to stress neurons. This drug was designed to help clear it away faster.
Where it stands
Complete Response Letter issued 4 November 2025
This programme went furthest of any in SCA. The FDA accepted the application in February 2025 and granted Priority Review, with a decision date of 15 August 2025. That date was extended by three months, and on 4 November 2025 the company announced the FDA had issued a Complete Response Letter — a decision not to approve the application in its current form. Reported reasons centred on the evidence itself: the pivotal study compared treated patients against separate natural-history cohorts rather than a group randomised alongside them, and the agency indicated a larger treatment effect would be needed to be confident that design was not producing a misleading result. A Complete Response Letter is not necessarily the end of a programme; companies can respond and resubmit. Check the company’s filings for the current position.
Many candidate drugs enter testing. Only a few reach approval. That is the base rate, not pessimism — worth holding in mind when reading hopeful news.
Why the troriluzole decision is worth understanding properly
It is the closest this condition has come to having an approved treatment, and the reason it did not get there is genuinely informative rather than just disappointing.
The central issue was the comparison. In a conventional trial, participants are assigned by chance to receive the drug or a placebo, and both groups are followed at the same time under the same conditions. That randomisation is what allows a difference between them to be attributed to the drug rather than to something about the people.
The pivotal evidence here instead compared treated patients against data from separate natural-history cohorts — people whose disease course had been documented elsewhere. This is called an externally controlled design, and in very rare diseases it is sometimes the only practical option. Its weakness is that the two groups can differ in ways nobody accounted for: who gets enrolled in a drug study, how they are assessed, and how carefully they are followed can all differ from a natural-history cohort, and any of those can produce an apparent benefit that is not the drug.
The reported reasoning was along these lines: given that risk, a larger effect would be needed before the agency could be confident the difference was real.
Two things follow, and both matter. A Complete Response Letter is a decision about an evidence package, not a verdict that a drug does not work — companies can address the issues and resubmit. And it is reasonable to hold two thoughts at once here: that people with a condition that has no treatment are poorly served by a slow bar, and that a bar that lets through treatments which do not work serves them worse. How the approval process works.
Broader directions being explored
Categories of approach rather than named programmes, because early-stage work changes fast and the live registry is a better guide to it than anything written here.
Turning down the faulty gene
If a repeat expansion causes the problem by making a harmful protein, one approach is to reduce how much of that protein gets made at all. Techniques that silence or edit a specific gene are being explored across the repeat-expansion diseases, and SCA3 has been a particular focus because its genetics are well characterised.
Protecting the cells under stress
Rather than targeting the gene, this approach tries to keep affected neurons — especially the Purkinje cells of the cerebellum — functioning for longer, by addressing things like protein clearance, mitochondrial function or excess glutamate signalling.
Measuring the disease better
A quieter but essential strand of work. Trials need a way to detect change over a year or two in a condition that progresses over decades. Work on rating scales, imaging and blood markers is what makes future trials able to give a clear answer at all — and, as the troriluzole decision showed, how a trial measures and compares can decide the outcome as much as the drug does.
Finding the causes still unnamed
Many people with inherited ataxia never receive a specific genetic answer. SCA27B, described only recently, turned out to explain a meaningful share of late-onset ataxia that had previously gone unlabelled. Gene discovery work continues to move people out of the unexplained category.