Metachromatic Leukodystrophy (MLD) is a rare genetic disease caused by a mutation in the ARSA gene. This mutation leads to the accumulation of sulfatides in the central and peripheral nervous systems, resulting in progressive dysmyelination, neuroinflammation, and neurodegeneration. The disease causes the loss of motor and cognitive functions, ultimately leading to death. MLD has three variants based on the age of symptom onset: late infantile, early juvenile, and late juvenile. The earlier the onset of symptoms or the presence of motor symptoms, the more severe and rapid the disease progression.
The FDA recently approved atidarsagene autotemcel, also known as arsa-cel or Lenmeldy, as the first gene therapy to treat children with MLD. The therapy involves a one-time single-dose infusion made from the patient’s hematopoietic stem cells that have been modified to include functional copies of the ARSA gene. Clinical trials and an expanded access program in Milan demonstrated the safety and effectiveness of arsa-cel in treating MLD. Patients who received the gene therapy showed a significant reduction in the risk of severe motor impairment or death compared to those who did not receive treatment.
Children with pre-symptomatic late infantile MLD who received arsa-cel were all alive at 6 years, a stark comparison to the natural history group where only 58% of children survived. Additionally, treated children showed improvements in walking ability, language skills, and performance IQ scores. Those with pre-symptomatic early juvenile and early symptomatic early juvenile MLD also exhibited slowing of motor or cognitive decline. The one-time treatment with arsa-cel has the potential to restore enzymatic function, which can stop or slow disease progression over a significant period.
Potential Risks and Adverse Events
While arsa-cel has shown promising results, there are potential risks and adverse events associated with the treatment. Common side effects include fever, low white blood cell counts, mouth sores, respiratory infections, rash, and infections. Patients may also experience complications such as blood clots, encephalitis, and an increased risk of blood cancer, although no cases have been reported. The FDA recommends lifelong monitoring for hematologic malignancies and regular blood count checks for at least 15 years after treatment.
The approval of arsa-cel gene therapy marks a significant milestone in the treatment of MLD, offering hope to children affected by this devastating disease. While the therapy has shown positive outcomes in clinical trials, it is essential to weigh the potential risks and adverse events associated with treatment. Regular monitoring and long-term follow-up are critical to ensuring the safety and efficacy of gene therapy for children with MLD.