Gene therapy takes steps forward in the fight against rare diseases. Eight children suffering from severe Hurler syndrome, a disease associated with reduced life expectancy, benefited from this therapy. The little ones are doing well, growing and have regained or maintained motor skills, skills that are severely compromised by the disease. The treatment, developed by the San Raffaele Telethon Institute for Gene Therapy in Milan (SR-Tiget), therefore shows a first favorable outcome. The results, still preliminary, are reported in an interim analysis (not yet the conclusive one, which contains the final data) published in the New England Journal of Medicine. With due caution, in short, today the first good news arrives.
Hurler’s syndrome – the most severe form of mucopolysaccharidosis type 1 – is a rare disease involving motor difficulties associated with skeletal defects, cognitive deficits, heart and breathing disorders, a pathological enlargement of the liver and spleen, along with a characteristic alteration of the facial expression. So much so that the disease can unfortunately lead to death as early as adolescence. Early diagnosis is essential as prompt treatment alleviates some symptoms and can slow the progression of the disease. Among the therapies already available, the first choice, for patients less than 2 and a half years old, concerns the transplantation of hematopoietic stem cells. This one-time surgery can preserve neurocognitive functions, improve some somatic features and extend life expectancy. Then, there is enzyme replacement therapy with laronidase (the disease is characterized by a lack of this enzyme), to be taken for life, which relieves some non-neurological symptoms.
Gene therapy, tested for the first time
But advanced therapies are currently being studied, including gene therapy, studied by the SR-Tiget group under the guidance of Alessandro Aiuti. For the first time, therefore, in Hurler’s syndrome, gene therapy has been tested in humans, for now in a small sample of children. We already knew that the safety profile, one of the central elements taken into consideration in the trials, turns out to be very good. Today, this is joined by new favorable results on efficacy, which indicate that the treatment is working. The researchers involved 8 families of children with Hurler’s syndrome, with an average age of nearly two years. Treatment involved autologous (by the patient himself) transplantation of hematopoietic stem cells and progenitor cells – cells that work together and serve as a tissue repair system – along with gene editing. In practice, a harmless viral vector is inserted that carries the gene modification to repair the damage underlying the disease, or to produce the missing enzyme, laronidase.
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The results: from cognitive to motor skills
In all of the young patients, the new cells with gene correction took root well within one month of transplantation and the result is being maintained in subsequent monitoring. The activity of the enzyme has been detected and is associated with the local elimination of large molecules called mucopolysaccharides, the accumulation of which is the basis of various symptoms of the disease. The brain and movement also benefited. In the preliminary analysis, in fact, the patients showed a stable cognitive performance, while the motor development proceeded and the ability to move did not decrease. The images of the brain and spine obtained with MRI also show consistent results and in some cases even improvements, along with a reduction in joint stiffness. The growth, then, is in line with the normal one according to the parameters indicated by the World Health Organization. In short, these first results, still initial, but promising, seem to indicate – and the hope is that in the future there will be confirmation, with lasting results – that the correction of the gene defect has been acquired and is effective.
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