New Data Presented on Gene Therapy for Hunter Syndrome

According to BioSpace, Homology Medicines has released the first round of data from the clinical trials of HMI-203, a gene therapy being developed for the treatment of Hunter syndrome, also known as mucopolysaccharidosis type II (MPS II). Initial data is positive, demonstrating that this therapy can cross the blood-brain barrier. Results will be presented at the 17th Annual WORLDSymposium™ Meeting.

About Hunter Syndrome

Hunter syndrome, also known as mucopolysaccharidosis II (MPS II), is an extremely rare, genetic disorder caused by a lack of the enzyme iduronate 2-sulfatase. This enzyme is responsible for breaking down complex molecules, and without it these molecules build up and damage the body. This damage gets progressively worse as time passes, and it eventually causes permanent damage that affects appearance, mental development, organ function, and physical abilities. This disorder is inherited through a chromosome from the mother and is far more common in males than females.

Due to the buildup of harmful molecules, symptoms do not begin to present until age two to four. They can be mild to severe depending on the person who has it. Symptoms include an enlarged head, thicker lips, a broad nose with flared nostrils, a protruding tongue, a deep or hoarse voice, abnormalities in the skeletal system, an distended abdomen due to enlarged internal organs, chronic diarrhea, white skin growths, joint stiffness, aggressive behavior, stunted growth, and delayed development. Along with these symptoms, Hunter syndrome can bring other complications depending on its severity. Respiratory, cardiac, brain, nervous system, skeletal, and connective tissue complications are all possible when one has this syndrome. There are currently no cures for this disorder, and treatment is symptomatic.

Data on HMI-203

Through the use of their AAVHSC vectors, Homology is able to target the peripheral and central nervous systems, as well as the peripheral organs. This advancement not only expands the company’s CNS platform, but it was able to successfully treat Hunter syndrome in preclinical models. Further results show that a single dose of HMI-203:

  • Caused biodistribution and the sustained expression of human I2S enzymes, which resulted in
    • The reduction of biomarkers that are key to Hunter syndrome in the liver, spleen, kidneys, heart, lungs, and brain
    • A significant reduction of heparan sulfate GAGs in samples of cerebrospinal fluid
  • Increased hI2S, which could potentially mean that HMI-203 has potential for cell cross-correction
  • In mouse models of Hunter syndrome, the mice who were treated with the gene therapy saw improvements in their paw deformities

Researchers are excited by these results, as they even support plans to move onto a Phase 1/2 trial later in 2021. Hopefully this treatment continues to demonstrate positive results and reach FDA approval, as Hunter syndrome patients currently face an unmet medical need.

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