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Breakthrough Gene Therapy for Maple Syrup Urine Disease Shows Promise in Animal Models

  • UMass Chan researchers have developed a gene therapy that successfully prevented death and normalized growth in animals with maple syrup urine disease, offering hope for patients with limited treatment options.

  • The therapy uses an adeno-associated viral vector to deliver functional gene copies of BCKDHA and BCKDHB, effectively restoring the body's ability to break down certain amino acids that cause toxic buildup.

  • A treated calf with MSUD grew normally over two years and transitioned to a normal high-protein diet, demonstrating the therapy's potential for human application where current treatments are limited to strict diets or liver transplants.

Researchers at the University of Massachusetts Chan Medical School have developed a promising gene therapy for maple syrup urine disease (MSUD), a rare genetic disorder that can cause life-threatening neurological damage. The therapy successfully prevented symptoms in mice and enabled a calf born with the disease to grow normally over two years, according to findings published in Science Translational Medicine.
MSUD is characterized by the body's inability to properly break down certain amino acids, leading to a toxic buildup that can cause severe neurological symptoms and brain damage. Currently, patients must either follow an extremely restrictive low-protein diet or undergo liver transplantation to manage the condition.

Novel Gene Therapy Approach

The research team, led by Dr. Jiaming Wang and colleagues, developed a gene replacement therapy that uses an adeno-associated viral vector (AAV9) to deliver functional copies of the BCKDHA and BCKDHB genes. These genes encode essential protein subunits of the branched chain alpha-keto acid dehydrogenase complex (BCKDH), which is dysfunctional in patients with MSUD.
"Simply put, we believe the gene therapy demonstrated in both animal species, especially in the cow, very well showcases the therapeutic potential for MSUD, in part because the diseased cow, without treatment, has a very similar metabolic profile as the patients," explained Dan Wang, PhD, assistant professor of genetic & cellular medicine at UMass Chan.
The therapy was designed to target the liver, muscle, heart, and brain – key tissues affected by the disease. In laboratory tests, the treatment worked as intended in knockout cells and proved safe in wild-type mice.

Remarkable Results in Animal Models

The most compelling evidence came from a calf born with classic MSUD. After receiving a single dose of the gene therapy modified to carry bovine genes, the calf not only survived but thrived. Over a two-year observation period, the animal grew normally and eventually transitioned to a standard high-protein bovine diet – something that would be impossible without effective treatment.
Similarly, the therapy prevented death after birth in mice deficient in either BCKDHA or BCKDHB genes, further validating its potential efficacy.

Disease Background and Prevalence

MSUD occurs in approximately one in 197,714 live births globally, but is significantly more common in certain populations. Among Mennonite communities in Lancaster County, Pennsylvania, the incidence rises to one in 400 births. The condition is also more prevalent in regions of Brazil, Portugal, Turkey, and the Philippines, as well as among people of Ashkenazi descent.
The disease results when a child inherits mutated forms of the BCKDHA, BCKDHB, or DBT gene from both parents. Without the proper functioning of these genes, the body cannot break down certain amino acids, leading to the characteristic sweet-smelling urine that gives the disease its name, along with potentially fatal neurological complications.

Collaborative Research Effort

The study represents a collaborative effort between researchers at UMass Chan Medical School and the Clinic for Special Children in Gordonville, Pennsylvania. Key investigators included Heather Gray-Edwards, DVM, PhD; Guangping Gao, PhD; and Kevin Strauss, MD.
"We believed gene therapy could be a breakthrough for patients with MSUD and, in August 2018, met on a cattle farm in Iowa to pursue that vision: to develop and test gene therapy in a unique animal model, a newborn calf with MSUD," said Dr. Strauss. "For people worldwide living with MSUD, this signifies major progress on the path to a brighter future."

Path to Clinical Application

The research team is now exploring the next steps with the U.S. Food and Drug Administration to translate this gene therapy into clinical use through a Phase I/II study. The therapy holds promise as a therapeutic alternative to the current limited options of prescription diet and liver transplant for treatment of MSUD types 1A and 1B, the two most common forms of the disease.
Before moving to human trials, the scientists plan to further characterize the long-term impact of the gene therapy on BCKDH levels in the brain and determine the treatment's benefits on cognition and behavior over extended study periods.
The study was partially funded through an agreement with ASC Therapeutics, a privately held biopharmaceutical company developing in-vivo gene replacement, gene editing, and allogeneic cell therapies.
For patients and families affected by this rare metabolic disorder, this breakthrough represents a significant step toward a potential one-time treatment that could eliminate the need for lifelong dietary restrictions or major surgery.
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