Hurler syndrome: 2026 so far

CSF biomarkers linked ERT timing and HCT effects.

In the months covered, one cohort report linked treatment timing to storage markers measured in cerebrospinal fluid (CSF, the fluid around the brain and spinal cord). IV enzyme replacement therapy (ERT) before hematopoietic cell transplantation (HCT, a stem cell transplant) was linked to lower CSF markers than being ERT-naive. The lowest CSF levels were reported around one year after HCT. In the same cohort, long-term IV ERT after HCT did not lower CSF markers further than HCT alone. This was reported even though urine GAG levels differed between the short- vs long-term post-HCT ERT groups. The report also said blood enzyme activity did not strongly match CSF marker levels in this dataset. This helps show how researchers are trying to measure brain-related storage effects, but this report did not establish how these CSF marker changes relate to day-to-day neurologic outcomes.

Research covered in: May 2026

Single-case gene therapy reports added both feasibility and risk signals.

In the months covered, several early-stage approaches aimed to improve IDUA delivery or expression, but human evidence was limited to single cases. One first-in-human report of intracisternal RGX-111 (delivered into fluid spaces around the brain) in a child with severe Hurler syndrome described mild side effects and normal brain imaging over more than five years. The child continued weekly IDUA infusions and did not receive HSCT. Separately, a different single case described a neuroepithelial tumor (a tumor from nervous-system lining cells) four years after intracisternal magna AAV9 gene therapy, with tumor testing suggesting clonal integration of rearranged vector elements into PLAG1. With only individual-case reports available, these findings highlight why long-term follow-up is a central part of gene-therapy research when both feasibility and serious risks can appear at the single-patient level.

Research covered in: April 2026, May 2026

Reports emphasized recurring hand issues and workable leg-alignment surgery.

In the months covered, reports highlighted that musculoskeletal and hand problems can remain active even when disease-specific systemic treatments are used. Single-center pediatric reviews described carpal tunnel syndrome (pressure on a wrist nerve causing numbness or pain) starting early in childhood, with recurrence after surgical release. They also reported trigger digits (fingers that catch or lock when bending) in 39% of children, with recurrence in some cases. Both reports noted storage-type cells in local tissues even after successful HSCT. Separately, a small hospital study suggested guided-growth tension-band plates corrected knock-knee-type alignment in children with Hurler (and Morquio) at rates not statistically different from idiopathic valgus cases. Together, these reports point to a need for ongoing monitoring and sometimes repeat procedures for hand and orthopedic function, while also suggesting some standard orthopedic techniques may still work in MPS-affected bone.

Research covered in: March 2026, April 2026, June 2026

More emphasis on confirmatory testing and consistent variant interpretation.

From January 2026 to September 2026, reports repeatedly showed that the diagnosis can depend on confirmatory testing and on how genetic variants are interpreted. Newborn screening program summaries suggested second-tier dried-blood-spot GAG testing (a follow-up test measuring stored sugars) was associated with a higher share of confirmed cases labeled severe and slightly fewer pseudodeficiency outcomes, while also leaving more cases temporarily "undetermined." A separate 10-year Tuscany program reported many initial positives but no confirmed MPS I cases after follow-up testing. Case-based diagnostic reports showed that broader genetic testing (for example, genome sequencing after exome sequencing) plus enzyme/urine testing can clarify attenuated MPS I when earlier testing misses key changes or when more than one genetic finding contributes to symptoms. One case also described MPS I recognition after a blood-smear clue in a child with another genetic diagnosis. In practice, these reports reinforce that an abnormal screen or partial genetic result often needs step-by-step follow-up (enzyme, urine, and broader genetics) before the diagnosis is considered settled.

Research covered in: January 2026, March 2026, April 2026, May 2026, September 2026

Small studies suggested progression signals needing longer-term monitoring.

New in the months covered, small reports suggested that some complications may keep changing over time and may not reliably stabilize with treatment. A very small mixed MPS I/MPS II follow-up (three patients) reported worsening upper-extremity nerve testing over five years despite ERT and after HSCT. The median nerve changed more than the ulnar nerve, and one patient later had no recordable median sensory signals on either side. In a Hurler mouse model, lung imaging and mechanics suggested uneven ventilation and combined airway and lung-tissue changes. Separately, a single post-HSCT death report identified pulmonary air emboli (air bubbles blocking lung blood vessels) linked to extensive bowel-wall gas at autopsy. These reports support why longer-term monitoring of neuropathy and respiratory status remains part of research and care planning, while the frequency and predictability of these issues were not established here.

Research covered in: February 2026, July 2026