February 2026 Research Update

In a small early study in very young boys with the neuronopathic form of Hunter syndrome, thinking and learning scores generally stayed stable over several years while a spinal fluid storage marker dropped and stayed low. [1] This combination points to a possible signal that delivering idursulfase directly into the spinal fluid may affect brain-related disease measures, but the results are still uncertain because there was no comparison group. [1] The study also showed that the practical side of long-term spinal delivery matters, because many reported issues were related to the delivery device rather than the drug itself. [1]

All participants received intrathecal idursulfase-IT (idursulfase given into the spinal fluid) in addition to weekly standard IV idursulfase, and they were followed for at least 3 years. [1] Cognitive test results did not show a clear pattern of steady improvement, but many scores did not decline quickly over time, which is why the authors described the overall pattern as stability. [1] In the spinal fluid, total glycosaminoglycans (a storage signal) fell markedly early and stayed low, while heparan sulfate dropped at first but tended to move back toward baseline later. [1]

Safety reports were described as generally tolerable, with no deaths or treatment discontinuations, but some serious problems occurred that were linked to the implanted delivery device, including infection. [1] The report also noted that many children had neutralizing antibodies in the blood and continued to have them, which adds context for how the body may react to enzyme therapy over time. [1]

This month adds an early, long-followed look at whether putting idursulfase into the spinal fluid might help slow worsening of brain-related symptoms in very young children, and it gives a clearer picture of what researchers are measuring to judge that. [1] The evidence is still early because only 9 children were included and there was no untreated or standard-care comparison, so the results cannot show for sure what would have happened without this approach. [1] Even so, the report helps clarify that long-term stability in cognitive testing plus changes in spinal fluid storage markers are being used as signals to watch, and it also highlights that device-related complications are an important part of the real-world burden being studied. [1]

A small case series suggests that hand and wrist nerve problems can continue to progress over years in MPS, even in children who have received disease-specific therapies. [2] The pattern described was more damage in the median nerve (often linked with carpal tunnel-type problems) than in the ulnar nerve, with sensory nerve signals affected more than motor signals. [2] Because this report includes only 3 patients across MPS types I and II, it is best read as a detailed look at what progression can look like rather than a prediction for everyone. [2]

Over 5 years of nerve testing in both arms, the median nerves showed signs consistent with worsening nerve injury, including features suggesting both loss of nerve fibers and damage to the nerve insulation. [2] Sensory signals in the median nerve tended to be more affected than motor signals, and ulnar nerves showed similar changes but with milder progression. [2] In the Hunter syndrome patient who started therapy later, the report described more severe median nerve involvement, including absent sensory signals in both wrists. [2]

This report adds detail to a concern many families already face: numbness, tingling, or hand weakness may reflect nerve damage that can build slowly over time. [2] The evidence here is exploratory and based on only 3 individuals, so it does not define how common or how fast these changes occur in Hunter syndrome. [2] Still, it helps clarify that long-term nerve testing can show progression in the median nerve and that sensory changes may be especially important to watch for in research and monitoring discussions. [2]