The problem with studying rare genetic epilepsies is that by the time you've figured out what's going wrong, you've usually discovered seventeen other things you didn't know the brain was doing in the first place. Case in point: SLC13A5 citrate transporter disorder, a condition so rare that roughly 120 people worldwide have been diagnosed with it, and yet it's teaching us something genuinely wild about how brains fuel themselves.

Your Brain Runs on Citrate (Who Knew?)

Here's something your biology textbook probably glossed over: citrate, that thing you vaguely remember from the Krebs cycle diagram you memorized and immediately forgot, is actually doing important work outside your cells too. In the brain, astrocytes (the support staff neurons rarely thank) pump citrate into the extracellular space, where neurons slurp it up through a transporter called NaCT, encoded by the SLC13A5 gene. This citrate helps regulate everything from energy production to how excitable your neurons get. It even chelates calcium and magnesium ions, which is a fancy way of saying it keeps your neurons from firing like an overcaffeinated intern on their first day.

When SLC13A5 is broken? Citrate piles up outside neurons with nowhere to go. The result: seizures starting in the first week of life, developmental delays, movement disorders, and even dental abnormalities, because apparently this transporter doesn't believe in doing just one job (Hardies et al., 2015; Bhutia et al., 2017).

Gene Therapy Enters the Chat

A team led by Rachel Bailey at the University of Texas Southwestern decided to ask the obvious (but technically very difficult) question: what if you just... gave these neurons a working copy of the gene?

Using an AAV9 viral vector carrying a functional human SLC13A5 gene, Bailey and colleagues delivered the therapy directly into the cerebrospinal fluid of knockout mice that model the human disorder. And the results were, frankly, the kind of thing that makes you do a double-take at your data before telling anyone (Bailey et al., 2026).

Treated mice showed decreased extracellular citrate levels. Their brain wave patterns normalized. Their messed-up sleep architecture (because of course this disorder also wrecks your sleep) straightened out. And when researchers tried to chemically induce seizures, the treated mice resisted them, while untreated knockouts did not. The therapy essentially told those neurons, "Here, take this gene, and go back to functioning like you're supposed to."

Timing Is (Mostly) Everything, Except When It Isn't

One of the more encouraging findings: the therapy worked whether delivered during early brain development or in young adult mice. For a disorder that hits in the first week of life, knowing you haven't necessarily missed the window by the time you get a diagnosis is a pretty big deal. Most rare diseases take years to diagnose, and a therapy with a narrow treatment window is about as useful as an umbrella you can only open indoors.

The team also compared two delivery routes in adult mice. Intra-cisterna magna injection (directly at the base of the skull) outperformed intrathecal lumbar puncture (lower back injection). More brain-targeted delivery meant better outcomes, which makes intuitive sense but is the kind of thing you still need to actually prove with data.

Why This Matters Beyond 120 Patients

SLC13A5 citrate transporter disorder currently has no disease-modifying treatment. Anti-seizure medications help some patients some of the time, but they're treating symptoms while the underlying metabolic chaos continues unchecked (Brown et al., 2024). Taysha Gene Therapies had been developing TSHA-105 for this condition and received both FDA orphan drug and rare pediatric disease designations, though the company has since deprioritized internal development and is seeking partners to advance the program.

This preclinical work from Bailey's lab provides the kind of robust, multi-endpoint evidence that could help push the therapy forward regardless of which company picks up the baton. It also adds to the growing body of evidence that AAV9-based gene therapies delivered to the CSF can meaningfully treat neurological disorders, following in the footsteps of Zolgensma for spinal muscular atrophy (Hoy, 2019).

For the families of kids seizing hundreds of times a day within their first week of life, "further development is supported" might be the most understated and hopeful sentence in the whole paper.

References:

1. Bailey LE, Adams RM, Schackmuth MK, et al. AAV-mediated gene therapy in a model of SLC13A5 citrate transporter disorder rescues epileptic and metabolic phenotypes. The Journal of Clinical Investigation. 2026. DOI: 10.1172/JCI197503. PMID: 41712282

2. Hardies K, de Kovel CGF, Weckhuysen S, et al. Recessive mutations in SLC13A5 result in a loss of citrate transport and cause neonatal epilepsy, developmental delay, and teeth hypoplasia. Brain. 2015;138(Pt 11):3238-3250. DOI: 10.1093/brain/awv263. PMID: 26384929

3. Bhutia YD, Kopel JJ, Lawrence JJ, Neugebauer V, Ganapathy V. Plasma membrane Na+-coupled citrate transporter (SLC13A5) and neonatal epileptic encephalopathy. Molecules. 2017;22(3):378. DOI: 10.1016/j.bbadis.2016.08.014. PMID: 27594413

4. Brown TL, Bainbridge MN, Zahn G, Nye KL, Porter BE. The growing research toolbox for SLC13A5 citrate transporter disorder. Therapeutic Advances in Rare Disease. 2024;5. DOI: 10.1177/26330040241263972. PMID: 39091529

5. Hoy SM. Onasemnogene abeparvovec: first global approval. Drugs. 2019;79(11):1255-1262. DOI: 10.1007/s40265-019-01217-1. PMID: 31270752

Disclaimer: The image accompanying this article is for illustrative purposes only and does not depict actual experimental results, data, or biological mechanisms.