Nicola Longo MD, PhD, and Mark Roberts, MD

Drs. Longo and Roberts discuss the current status of gene therapies in rare neuromuscular disorders in this eight-part podcast series. This is derived from the symposium that was presented at WORLDSymposium 2025 in San Diego, California on February 4th-7th 2025 and is intended for healthcare professionals only.

This podcast includes information about investigational compounds that do not yet have a regulatory approval or authorization for a specific indication. The safety and efficacy of the agents under investigation have not been established and contents of this podcast shall not be used in any manner to directly or indirectly promote or sell the product for unapproved uses.

The views, thoughts, and opinions expressed in this presentation belong solely to the author and are subject to change without notice. The contents of this presentation do not constitute an endorsement of any product or indication by Astellas. In this part, Dr. Longo will discuss the current treatment landscape and limitations in lysosomal disorders.

Nicola Longo MD, PhD
What I want to do today, is just place gene replacement therapy within the current landscape of lysosomal storage disorder treatment therapy. Gene therapy obviously has the potential of treating lysosomal disorder to correct the root cause of lysosomal storage disorder. The gene is defective, and what happen is that you can potentially either fix the gene or bypass the lack of the genetic product. But there are already therapies that are existing and are functioning. Obviously, in many cases, the lysosomal disorder is caused by defective production of an enzyme, which is defective.

We can either replace the enzyme with enzyme replacement therapy, or provide chaperone for specific mutations that retain the synthesis of the enzyme, that however is not very functional. Another avenue that it is being reported is the utilization of substrate reduction therapy. A substrate accumulates, you prevent the synthesis of the substrate to reduce the accumulation of toxic material. What we know now is that this is not enough to produce many lysosomal disorders. In many cases, the lysosomal disorder result sometime in impairment of intracellular trafficking, and sometime in the function of other organelles.

At the end, it results in the activation of the macrophagic system and inflammation. Already we have some therapy acting at this level. The end result of lysosomal storage disorder, there will be cell suffering and cell death, leading to a progression of the disease, and morbidity and mortality. Now, what therapy do we have available already? Obviously, hematopoietic stem cell transplantation has been around for quite some time.

It has been the same thing that we do with gene therapy, except that instead of reintroducing the gene of the subject, we place gene of a subject who is not affected of the disease. This therapy has been proven effective in cases of MPS-1 and alpha-mannosidosis. But in many cases this has to be given way before symptoms start to be affected.

Enzyme replacement therapy has been around for quite some time, starting with Gaucher disease, and now that it is available for a list of diseases that are there, so it's like Fabry, Gaucher, Pompe, different types of mucopolysaccharidosis, alpha-mannosidosis, acid lipase deficiency, 1 neuronal ceroid lipofuscinosis, and Niemann-Pick type A and B.

Obviously the advantage of this therapy, they give back the enzyme that it is defective. But the disadvantage that many time they cannot enter specialized areas such as the brain. There is already the second generation of enzyme replacement therapy that it is available. With this second generation, some of the newer drugs are more effective in terms of cellular uptake, or in terms of having a prolonged half-life and prolonged activity.

Then there are pharmacological chaperone therapy, and the one which is FDA approved is migalastat for Fabry disease, under study is ambroxol for Gaucher disease. The disadvantage of this therapy that only a selected number of mutations respond to this therapy.

Substrate reduction therapy has been introduced for Gaucher disease many years ago with miglustat, and it was followed by eliglustat. Both of them are effective, and some of them more effective than other, simply because of the fewer side effects of eliglustat as compared to miglustat. But at the same time, eliglustat does not pass the blood brain barrier.
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Finally, the newer agents that are already administered, N-acetyl-L-leucine and arimoclomol, both approved for Niemann-Pick type C, they act more on the downstream effect of the lysosomal storage disorder, either by stabilizing neuronal cell activity or by reducing the inflammation that is present in the brain.

In the next part, Dr. Longo will discuss gene replacement therapy in lysosomal disorders.