April 2026 Research Update

Studies this month suggest that newborn screening for Hunter syndrome can find affected babies early, but it also turns up many babies who look positive on the first test yet do not have the condition. Adding a second step that measures glycosaminoglycan (GAG) markers, and using more detailed urine testing when results are unclear, appeared to help separate true Hunter syndrome from look-alike results. The picture that emerges is that screening works best as a multi-step process, not a single yes/no test. [1] [2]

In a North Carolina pilot that screened about 220,000 newborns, 33 babies screened positive based on low iduronate-2-sulfatase (I2S) activity, but only 2 were confirmed with Hunter syndrome and 31 were labeled pseudodeficiency (a low enzyme result without the disease). A second-tier blood marker (an endogenous non-reducing end, or NRE, GAG ratio) was elevated only in the confirmed Hunter syndrome cases and lined up with confirmatory urine GAG results, pointing to a way to reduce false alarms from the first-tier enzyme test. This matters because fewer false positives can mean fewer families going through prolonged uncertainty and repeat testing. [1]

A separate report describing four unrelated families found after positive newborn screening focused on what to do when early follow-up testing does not give a clear answer. It highlighted that fractionated urine GAG testing (a more detailed look at the types of GAGs in urine) can help confirm or clarify Hunter syndrome when enzyme testing, total urine GAGs, or IDS gene sequencing are inconclusive. Taken together with the pilot screening work, this reinforces that follow-up testing choices can strongly affect how quickly a family gets a clear diagnosis. [2]

For families going through newborn screening, these studies add a clearer message: an initial screen can be a starting point, but it may not be the final answer. This may matter now in places using newborn screening, because adding specific GAG marker testing could reduce the number of families told there is a possible problem when there is not. What remains uncertain is how these approaches will perform across different programs and populations, since this month includes one state pilot and a small set of families with uncertain results. [1] [2]

Case reports this month broaden what Hunter syndrome can look like and add new genetic variants that may cause it. One report described Hunter syndrome showing up mainly as progressive eye problems in adulthood, which is not how many families picture the condition. Another report used computer modeling to explain how a newly found IDS gene change could disrupt the enzyme and the GAG breakdown pathway. Together, these reports mainly add to recognition and understanding rather than proving how common these situations are. [3] [4]

In one 44-year-old man, the main symptoms were progressive night blindness and distinctive retina changes on eye imaging, with testing showing reduced IDS enzyme activity and elevated urine GAGs (including increased heparan sulfate). The authors described this as an attenuated Hunter syndrome presentation linked to a novel IDS variant (c.707A>G, p.Lys236Arg). The practical meaning is that, in rare situations, eye findings may be a major clue that leads to testing for Hunter syndrome. [3]

In a male infant with Hunter syndrome, a different novel IDS change (a frameshift mutation, c.1133delA) was analyzed with structural and metabolic computer models. The modeling suggested the change would remove an important part of the enzyme and disrupt its binding pocket, with predicted buildup of GAG-related breakdown products while leaving broader metabolism mostly unaffected. This helps explain why this specific variant is likely disease-causing, but it does not by itself show how the child will do over time. [4]

For patients and caregivers, these reports mainly matter as awareness and diagnosis information rather than something that changes treatment right now. They highlight that Hunter syndrome can sometimes present in unexpected ways, including an eye-dominant picture in an adult, and that new IDS gene variants keep being identified. What remains uncertain is how often these presentations occur, because each report describes a single person and may not apply to most families. [3] [4]