What Are the New Treatments for GSD IV and APBD?

Currently, there is no definitive cure for Adult Polyglucosan Body Disease (APBD) or Glycogen Storage Disease Type IV (GSD IV). While liver transplantation is sometimes used for classic, early-onset GSD IV patients with severe liver failure, it is not a treatment for APBD, which is primarily an adult-onset neurological condition ^[1]. Furthermore, a liver transplant does not halt or reverse the progression of the disease in the brain, nerves, or muscles ^[1].

However, the landscape of future therapies is rapidly evolving. Researchers are actively developing new experimental treatments aimed at the root cause of both conditions: the accumulation of abnormal, poorly branched glycogen known as polyglucosan bodies ^[2]. Most of these therapies are currently in the preclinical stage (tested in laboratories and animal models—a process that often takes several years before human testing begins) or early clinical trials for related conditions. The main avenues of research include substrate reduction therapy, polyglucosan-degrading agents, and gene therapies.

Substrate Reduction Therapy (SRT)

Rather than trying to fix the defective branching enzyme, Substrate Reduction Therapy (SRT) aims to slow down the body’s production of glycogen in the first place ^[3]. If the body makes less normal glycogen, there is less raw material available to be misfolded into toxic polyglucosan bodies ^[4].

Scientists are targeting an enzyme called Glycogen Synthase 1 (GYS1), which is responsible for building glycogen.

• Genetic Knockdown (ASOs): Antisense oligonucleotides (ASOs) like UX053 are synthetic genetic molecules designed to block the production of GYS1 ^[5]. While UX053 and similar ASOs have primarily been researched for other glycogen storage diseases (like Pompe disease and GSD III), the mechanism of targeted glycogen reduction is highly applicable to GSD IV and APBD ^[3][6].
• Oral GYS1 Inhibitors: Small-molecule drugs (such as MZE001 and MZ-101) are being developed as oral medications to inhibit GYS1 ^[6][7]. In a recent early-stage human clinical trial (Phase 1) in healthy subjects, MZE001 was shown to be well-tolerated and successfully reduced muscle glycogen stores ^[8]. These findings provide strong proof-of-concept that oral SRT could eventually be tested in patients with APBD and GSD IV.

Clearing Existing Damage: 144DG11

While SRT stops the buildup of new polyglucosan bodies, other experimental drugs aim to clear out the toxic deposits that have already formed. 144DG11 is a novel, experimental compound designed to target the lysosome, the cell’s natural “recycling center” ^[9].

By interacting with a specific protein on the lysosome (LAMP1), 144DG11 enhances the cell’s ability to break down and clear away accumulated polyglucosan ^[9]. In mouse models of APBD, treatment with 144DG11 significantly reduced glycogen deposits in the brain, liver, heart, and peripheral nerves ^[9]. Furthermore, the treated mice showed improved survival rates and motor function ^[9]. 144DG11 is currently a preclinical candidate, meaning it must undergo further safety testing before it can advance to human clinical trials.

Gene Therapy and Genetic Repair

A critical challenge in treating the neurological symptoms of APBD is the blood-brain barrier—a protective cellular shield that keeps many traditional drugs from reaching the brain. Researchers are using gene therapy and targeted molecules to bypass this barrier and correct the underlying genetic defect in the GBE1 gene.

• AAV Gene Therapy: Researchers use modified, harmless viruses known as Adeno-Associated Viruses (AAV) as delivery vehicles ^[10]. The goal is to deliver a functional copy of the GBE1 gene directly into the patient’s cells ^[11], or to deliver RNA interference (RNAi) that reduces GYS1 directly in the brain, thereby lowering polyglucosan bodies ^[12]. While AAV therapy is highly promising, scientists must carefully navigate challenges such as immune system reactions ^[13][14].
• Targeting Mis-splicing: For APBD patients with specific genetic mutations, scientists are developing specialized ASOs designed to correct the “mis-splicing” (incorrect reading) of the GBE1 gene, allowing the body to produce a functional enzyme ^[15].
• Small Molecule Chaperones: Researchers are screening for chemical “chaperones” that can attach to the defective branching enzyme, stabilizing its structure so it can function properly ^[15][16].

The Importance of Natural History Studies

While you cannot currently access these experimental therapies outside of a research setting, enrolling in a natural history study is a proactive step you can take today ^[17]. Natural history studies track how the disease progresses over time without experimental treatment. These studies provide the crucial baseline data that future clinical trials will use to prove whether a new drug like 144DG11 or an AAV gene therapy is actually working ^[17].

How to find a study:
You can actively search for enrolling studies on ClinicalTrials.gov by typing in “Adult Polyglucosan Body Disease” or “Glycogen Storage Disease Type IV”. Additionally, connecting with patient advocacy organizations, such as the APBD Research Foundation or the Association for Glycogen Storage Disease (AGSD), can help you stay informed about upcoming trial opportunities.