July 2026 Research Update

This month added more reassurance that idursulfase beta (Hunterase), an enzyme replacement therapy, can be continued long term and can also be used after switching from idursulfase (Elaprase) without obvious new safety problems. In both longer follow-up and routine-care switching, urine markers of stored sugars (urinary GAG) stayed lower, and a walking test tended to stay stable or improve. This helps fill in a common real-life question for families: what happens when a person changes from one infused enzyme product to another. [1] [2]

In a 2-year open-label extension, people who continued idursulfase beta had sustained improvements in urinary GAG and in 6-minute walk distance compared with their baseline, and those who switched from idursulfase showed comparable patterns without new safety signals. The report also tracked immune responses to the drug, with anti-drug antibodies peaking early and then declining over time, while neutralizing antibodies were present in a minority of patients at different time points. For patients, this adds context for why lab monitoring may include both disease markers (like urinary GAG) and immune markers (antibodies) during longer-term treatment. [1]

A separate report from Belarus described 7 people who switched from idursulfase to idursulfase beta during a drug shortage and were followed in routine care. After the switch, urinary GAG levels continued to decrease, the 6-minute walk test stayed stable or improved during follow-up, and ultrasound measurements suggested further decreases in liver and spleen enlargement, without new safety concerns noted in that chart review. Because antibodies were not measured in this retrospective report, it cannot clarify how immune responses may have contributed to individual experiences. [2]

For families using enzyme infusions, these studies mainly add longer-term and real-world information about what has been observed when idursulfase beta is continued or when a switch from idursulfase happens for practical reasons. The evidence here is from an extension study and a small observational series, so it helps describe patterns seen in treated groups rather than proving exactly why changes happened. What remains uncertain is how well these results predict outcomes for every individual, especially for symptoms not captured well by urinary GAG or a walking test, and for people who may have different antibody responses over time. [1] [2]

This month included early evidence about a combined approach aiming to reach the brain in neuronopathic Hunter syndrome: delivering enzyme directly into the fluid around the brain and then performing umbilical cord blood transplantation. In three children, two identified through newborn screening and one an affected sibling, the transplant successfully took hold, and the brain-fluid storage marker (CSF heparan sulfate) moved in the expected direction with treatment timing, while development was reported as age-appropriate during the observation period. Taken together, this is an early signal that starting brain-directed treatment very early may be feasible and measurable, but it is not yet proof of long-term benefit. [3]

In this small case series, CSF heparan sulfate decreased within 3 months after starting intracerebroventricular idursulfase beta (given through an implanted access device), increased temporarily when enzyme treatment was paused for transplant, and decreased again after restarting. The study also reported increased enzyme activity in blood cells after transplant, supporting that the donor cells were producing the missing enzyme. For families, it helps clarify how CSF heparan sulfate may act as a short-term readout of how brain-targeted treatment is affecting storage levels. [3]

Safety-wise, there were no cases of chronic graft-versus-host disease or bacterial meningitis reported during the period described. One child developed sinusoidal obstruction syndrome but recovered after intensive care, and the same child later developed hypothyroidism. These details matter because they show the kind of close monitoring and hospital-based care that can come with combining brain-directed enzyme delivery and transplantation. [3]

A separate transplant report from Vietnam described outcomes of unrelated single-unit cord blood transplantation across 12 children with different immune and metabolic disorders, including Hunter syndrome as one of the diagnoses. It found cord blood transplantation was feasible in that center, with engraftment in most patients and an overall survival of 11 out of 12, alongside notable risks such as acute graft-versus-host disease and infections. This broader context helps patients understand that transplant outcomes are often discussed across mixed disease groups, and that risks and benefits may vary by condition and by individual situation. [4]

For families affected by neuronopathic Hunter syndrome, these studies mainly add early, real-world information about approaches that try to address brain involvement when started very early, and about how cord blood transplantation has played out in small groups. This evidence is exploratory and includes a 3-person series plus a mixed-diagnosis transplant cohort, so it is best viewed as a step in learning what is feasible and how to track effects (like CSF heparan sulfate), rather than a settled answer about long-term outcomes. What remains uncertain is how durable developmental results are over many years, and how often complications occur when these approaches are used more widely. [3] [4]

This month added to the catalog of genetic changes that can cause Hunter syndrome by reporting variants in the IDS gene in three unrelated boys from Tunisia. The key update was a newly described deep intronic deletion (a change in a non-coding region) linked to lower IDS RNA levels, alongside two missense variants expected to disrupt how the enzyme works. For families, this matters because it shows why genetic testing sometimes needs to look beyond the most obvious coding regions to fully explain a person's diagnosis. [5]

The study also used computer-based structural modeling to describe how the two missense variants might change the enzyme's shape near important working parts of the protein, which could make the enzyme less able to do its job. This kind of modeling does not measure symptoms directly, but it can help researchers connect a specific genetic change to a likely impact on enzyme function. In the longer run, more complete variant lists can improve molecular diagnosis and support future genotype-phenotype research. [5]

For patients and caregivers, this is mainly diagnosis-focused research rather than a treatment study. It may matter most for families going through genetic confirmation, variant interpretation, or family planning discussions, because it expands the range of IDS changes that laboratories may look for. What remains uncertain is how well these specific variants predict the exact course for an individual person, since the report focuses on genetics and predicted effects rather than long-term clinical outcomes. [5]