Clinical investigator perspectives on patient outcomes in children with neuronopathic mucopolysaccharidosis II during intrathecal idursulfase-IT treatment

BACKGROUND

Mucopolysaccharidosis II (MPS II) is a rare lysosomal storage disease characterized by iduronate-2-sulfatase gene (IDS) deficiency and downstream glycosaminoglycan accumulation. Two-thirds of patients present with neuronopathic disease and evaluating cognitive function in these patients is challenging owing to limitations of currently available tests. During the clinical development of intrathecal idursulfase (idursulfase-IT), regulatory authorities requested qualitative data to further understand the neurocognitive changes observed by the investigators through the clinical trials.

RESULTS

This qualitative study consisted of semi-structured interviews with all nine of the principal investigators who participated in the idursulfase-IT phase 2/3 (NCT02055118) and extension (NCT02412787) trials. These investigators enrolled the 56 patients with neuronopathic MPS II who qualified for the extension phase of the trial. The investigators were asked to rate the disease status of their patients. Of the 56 patients, 49 (88%) were rated as having disease that was improved/improving, stabilized or slowing progression compared with the expected outcomes with no treatment. Three patients were rated as worsening, while the remaining four patients were considered to have slowing progression or worsening disease. Similar results were demonstrated for patients aged from 3 to under 6 years at baseline, with 33 of 39 patients (85%) rated as having disease that was improved/improving, stabilized or slowing progression. Of the seven patients rated with slowing progression/worsening or worsening disease, five of them had an IDS variant other than missense, while two had a missense class variant. All the assigned improved/improving ratings were in patients receiving idursulfase-IT from the start of the phase 2/3 trial. Moreover, patients under 3 years of age at baseline were all rated as either improved/improving or stabilized disease. In a blinded review of patient profiles, investigators were requested to assign a disease status rating to 18 patients with large IDS deletions; 67% of these patients were rated as improved/improving or stabilized disease.

CONCLUSIONS

This qualitative analysis provides a snapshot of clinicians' considerations when evaluating treatment in patients with neuronopathic MPS II, compared with the expected decline in cognitive function in the absence of treatment. The results highlight the importance of robust assessment tools in treatment evaluation.

Caregiver experiences and observations of intrathecal idursulfase-IT treatment in a phase 2/3 trial in pediatric patients with neuronopathic mucopolysaccharidosis II

BACKGROUND

Approximately two-thirds of patients with mucopolysaccharidosis II (MPS II) have a severe, neuronopathic phenotype, characterized by somatic, cognitive, and behavioral issues. Current standard of care for the treatment of MPS II is enzyme replacement therapy with intravenous recombinant human iduronate-2-sulfatase (idursulfase). To target cognitive manifestations of MPS II, idursulfase has been formulated for intrathecal administration into the cerebrospinal fluid (idursulfase-IT). In accordance with recommendations for patient-focused drug development, semi-structured interviews were conducted to assess caregiver experiences and observations in a 52-week phase 2/3 trial of idursulfase-IT, in addition to intravenous idursulfase in pediatric patients with neuronopathic MPS II, or a substudy which enrolled patients younger than 3 years old, all of whom received idursulfase-IT.

RESULTS

Overall, 46 caregivers providing care for 50 children (mean [range] age 7.9 [3-17] years at interview) took part in a single 60-min exit interview; six of these children had participated in the substudy. Qualitative and quantitative data were obtained demonstrating the burden of MPS II experienced by caregivers and their families. Following participation in the trials, 39 (78%) of the children were reported by their caregivers to have experienced improvements in the symptoms and impact of disease. Of those with improvements, 37 (95%) experienced cognitive improvements and 26 (67%) experienced emotional/behavioral improvements. Overall, 43 children (86%) were rated by caregivers as having moderate or severe symptoms before the trials; after the trials, 28 children (56%) were considered to have mild or no symptoms. For the six children who participated in the substudy, these proportions were 83% and 100%, respectively. Caregivers' qualitative descriptions of trial experiences suggested improvements in children's verbal and non-verbal functioning and spatial and motor skills, as well as a positive impact on family life.

CONCLUSIONS

This study revealed caregiver-reported improvements in children's MPS II symptoms and the impact of the disease on patients and their families. There was a trend for cognitive improvement and a reduction in severity of MPS II symptoms. After many years of extensive review and regulatory discussions of idursulfase-IT, the clinical trial data were found to be insufficient to meet the evidentiary standard to support regulatory filings.

Intracerebroventricular enzyme replacement therapy in patients with neuronopathic mucopolysaccharidosis type II: Final report of 5-year results from a Japanese open-label phase 1/2 study

Intravenous idursulfase is standard treatment for mucopolysaccharidosis II (MPS II) in Japan. In the interim analysis of this open-label, phase 1/2 study (Center for Clinical Trials, Japan Medical Association: JMA-IIA00350), intracerebroventricular (ICV) idursulfase beta was well tolerated, suppressed cerebrospinal fluid (CSF) heparan sulfate (HS) levels, and stabilized developmental decline over 100 weeks in Japanese children with MPS II. Here, we report the final study results, representing 5 years of ICV idursulfase beta treatment. Six male patients with MPS II and developmental delay were enrolled starting in June 2016 and followed until March 2021. Patients received up to 30 mg ICV idursulfase beta every 4 weeks. Outcomes included CSF HS levels, developmental age (DA) (assessed by the Kyoto Scale of Psychological Development), and safety (adverse events). Monitoring by laboratory biochemistry tests, urinary uronic tests, immunogenicity tests, and head computed tomography or magnetic resonance imaging were also conducted regularly. Following ICV idursulfase beta administration, mean CSF HS concentrations decreased from 7.75 μg/mL at baseline to 2.15 μg/mL at final injection (72.3% reduction). Mean DA increased from 23.2 months at screening to 36.0 months at final observation. In five patients with null mutations, mean DA at the final observation was higher than or did not regress compared with that of historical controls receiving intravenous idursulfase only, and the change in DA was greater in patients who started administration aged ≤3 years than in those aged >3 years (+28.7 vs -6.5 months). The difference in DA change versus historical controls in individual patients was +39.5, +40.8, +17.8, +10.5, +7.6 and - 4.5 (mean + 18.6). Common ICV idursulfase beta-related adverse events were vomiting, pyrexia, gastroenteritis, and upper respiratory tract infection (most mild/moderate). These results suggest that long-term ICV idursulfase beta treatment improved neurological symptoms in Japanese children with neuronopathic MPS II.

Enhanced osteoblastic differentiation of parietal bone in a novel murine model of mucopolysaccharidosis type II

Mucopolysaccharidosis type II (MPS II, OMIM 309900) is an X-linked disorder caused by a deficiency of lysosomal enzyme iduronate-2-sulfatase (IDS). The clinical manifestations of MPS II involve cognitive decline, bone deformity, and visceral disorders. These manifestations are closely associated with IDS enzyme activity, which catalyzes the stepwise degradation of heparan sulfate and dermatan sulfate. In this study, we established a novel Ids-deficient mice and further assessed the enzyme's physiological role. Using DNA sequencing, we found a genomic modification of the Ids genome, which involved the deletion of a 138-bp fragment spanning from intron 2 to exon 3, along with the insertion of an adenine at the 5' end of exon 3 in the mutated allele. Consistent with previous data, our Ids-deficient mice showed an attenuated enzyme activity and an enhanced accumulation of glycosaminoglycans. Interestingly, we noticed a distinct enlargement of the calvarial bone in both neonatal and young adult mice. Our examination revealed that Ids deficiency led to an enhanced osteoblastogenesis in the parietal bone, a posterior part of the calvarial bone originating from the paraxial mesoderm and associated with an enhanced expression of osteoblastic makers, such as Col1a and Runx2. In sharp contrast, cell proliferation of the parietal bone in these mice appeared similar to that of wild-type controls. These results suggest that the deficiency of Ids could be involved in an augmented differentiation of calvarial bone, which is often noticed as an enlarged head circumference in MPS II-affected individuals.

Neurodevelopmental status and adaptive behavior of pediatric patients with mucopolysaccharidosis II: a longitudinal observational study

BACKGROUND

Mucopolysaccharidosis (MPS) II is a rare, X-linked lysosomal storage disease. Approximately two-thirds of patients have central nervous system involvement with some demonstrating progressive cognitive impairment (neuronopathic disease). The natural history of cognitive and adaptive function in patients with MPS II is not well-defined. This 2-year, prospective, observational study evaluated the neurodevelopmental trajectories of boys with MPS II aged ≥ 2 years and < 18 years.

RESULTS

Overall, 55 patients were enrolled. At baseline, mean (standard deviation [SD]) age was 5.60 (3.32) years; all patients were receiving intravenous idursulfase. Cognitive and adaptive function were assessed using the Differential Ability Scales, Second Edition (DAS-II) General Conceptual Ability (GCA) and the Vineland Adaptive Behavior Scales, Second Edition (VABS-II) Adaptive Behavior Composite (ABC) scores, respectively. Baseline mean (SD) DAS-II GCA and VABS-II ABC scores were 78.4 (19.11) and 83.7 (14.22), respectively, indicating low cognitive function and moderately low adaptive behavior. Over 24 months, modest deteriorations in mean (SD) scores were observed for DAS-II GCA (-3.8 [12.7]) and VABS-II ABC (-2.0 [8.07]). Changes in DAS-II GCA scores varied considerably, and data suggested the existence of four potential patient subgroups: (1) patients with marked early impairment and rapid subsequent decline, (2) patients with marked early impairment then stabilization, (3) patients with mild early impairment then stabilization, and (4) patients without impairment who remained stable. Subgroup analyses revealed numerically greater DAS-II GCA score reductions from baseline in patients aged < 7 years at baseline (vs. those aged ≥ 7 years) and in patients with DAS-II GCA scores ≤ 70 at baseline (vs. those with scores > 70); between-group differences were nonsignificant. No clear subgroups or patterns were identified for individual changes in VABS-II ABC scores. In total, 49 patients (89.1%) reported ≥ 1 adverse event (AE) and nine patients (16.4%) reported serious AEs.

CONCLUSIONS

Some patients with MPS II had rapid declines in cognitive ability, whereas others remained relatively stable after an initial decline. These insights provide a basis for more detailed analyses of different patient subgroups, which may enhance the definition and understanding of factors that influence cognitive and adaptive function in MPS II.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT01822184. Registered retrospectively: April 2, 2013.

A post hoc analysis of Projected Retained Ability Scores (PRAS) for the longitudinal assessment of cognitive functioning in patients with neuronopathic mucopolysaccharidosis II receiving intrathecal idursulfase-IT

BACKGROUND

Norm-based scores used to assess cognitive ability have clinical value when describing functioning of patients with neuronopathic disorders compared with unaffected, same-age peers. However, they have limitations when used to assess change in cognitive ability between two timepoints, especially in children with severe cognitive decline. Calculation of Projected Retained Ability Scores (PRAS) is a novel method developed to characterize absolute change in norm-based ability test scores. In this analysis, PRAS were calculated post hoc for children with mucopolysaccharidosis II (MPS II; Hunter syndrome) and early cognitive impairment in a 52-week phase 2/3 randomized controlled trial (RCT) and its extension study of intrathecal idursulfase (idursulfase-IT). Patients completing the first year of the extension after receiving idursulfase-IT in the RCT and extension (n = 32 of 34 enrolled) or the extension only (n = 15 of 15 enrolled) were categorized according to changes in Differential Ability Scales, Second Edition, General Conceptual Ability (DAS-II GCA) scores and PRAS at 1 and 2 years. Analyses were conducted in the overall population and a subpopulation aged < 6 years at baseline (idursulfase-IT in the RCT and extension [n = 27] and extension only [n = 12]).

RESULTS

PRAS methodology differentiated patients with decreases in DAS-II GCA scores into three separate categories reflecting below-average cognitive growth rates, plateauing cognitive development, and deteriorating cognitive functioning. After 1 year in the RCT, 72.4% of patients who initiated idursulfase-IT had above-average or average cognitive growth rates in DAS-II GCA scores compared with 53.3% of those who did not receive idursulfase-IT; 6.9% versus 20.0% experienced deteriorating cognitive functioning. Similar results were seen in children aged < 6 years: 76% (idursulfase-IT group) versus 50% (no idursulfase-IT) had above-average or average cognitive growth rates in DAS-II GCA scores; 4% versus 17% had deteriorating cognitive functioning. The difference in the distributions of cognitive categories at 1 year in children aged < 6 years was significant (p = 0.048). At 2 years, the proportions of patients in different cognitive categories were more similar between treatment groups.

CONCLUSIONS

PRAS methodology may help to differentiate changes in cognitive development in MPS II, and therefore may represent a valuable addition to existing approaches for interpreting changes in cognitive scores over time.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02055118 (registration date: 4 February 2014) and NCT02412787 (registration date: 9 April 2015).

Cognitive and adaptive behaviors associated with disease severity and genotype in patients with mucopolysaccharidosis II

BACKGROUND

Mucopolysaccharidosis II (MPS II) is a rare, X-linked lysosomal storage disease caused by pathogenic variants of the iduronate-2-sulfatase gene (IDS) and is characterized by a highly variable disease spectrum. MPS II severity is difficult to predict based on IDS variants alone; while some genotypes are associated with specific phenotypes, the disease course of most genotypes remains unknown. This study aims to refine the genotype-phenotype categorization by combining information from the scientific literature with data from two clinical studies in MPS II.

METHODS

Genotype, cognitive, and behavioral data from 88 patients in two clinical studies (NCT01822184, NCT02055118) in MPS II were analyzed post hoc in combination with published information on IDS variants from the biomedical literature through a semi-automated multi-stage review process. The Differential Ability Scales, second edition (DAS-II) and the Vineland Adaptive Behavior Scales™, second edition (VABS-II) were used to measure cognitive function and adaptive behavior.

RESULTS

The most common category of IDS variant was missense (47/88, 53.4% of total variants). The mean (standard deviation [SD]) baseline DAS-II General Conceptual Ability (GCA) and VABS-II Adaptive Behavior Composite (ABC) scores were 74.0 (16.4) and 82.6 (14.7), respectively. All identified IDS complete deletions/large rearrangements (n = 7) and large deletions (n = 1) were associated with a published 'severe' or 'predicted severe' progressive neuronopathic phenotype, characterized by central nervous system involvement. In categories comprising more than one participant, mean baseline DAS-II GCA scores (SD) were lowest among individuals with complete deletions/large rearrangements 64.0 (9.1, n = 4) and highest among those with splice site variants 83.8 (14.2, n = 4). Mean baseline VABS-II ABC scores (SD) were lowest among patients with unclassifiable variants 79.3 (4.9, n = 3) and highest among those with a splice site variant 87.2 (16.1, n = 5), in variant categories with more than one participant.

CONCLUSIONS

Most patients in the studies had an MPS II phenotype categorized as 'severe' or 'predicted severe' according to classifications, as reported in the literature. Patients with IDS complete deletion/large rearrangement variants had lower mean DAS-II GCA scores than those with other variants, as well as low VABS-II ABC, confirming an association with the early progressive 'severe' (neuronopathic) disease. These data provide a starting point to improve the classification of MPS II phenotypes and the characterization of the genotype-phenotype relationship.

Intrathecal idursulfase-IT in patients with neuronopathic mucopolysaccharidosis II: Results from a phase 2/3 randomized study

Two-thirds of patients with mucopolysaccharidosis II (MPS II; Hunter syndrome) have cognitive impairment. This phase 2/3, randomized, controlled, open-label, multicenter study (NCT02055118) investigated the effects of intrathecally administered idursulfase-IT on cognitive function in patients with MPS II. Children older than 3 years with MPS II and mild-to-moderate cognitive impairment (assessed by Differential Ability Scales-II [DAS-II], General Conceptual Ability [GCA] score) who had tolerated intravenous idursulfase for at least 4 months were randomly assigned (2:1) to monthly idursulfase-IT 10 mg (n = 34) via an intrathecal drug delivery device (IDDD; or by lumbar puncture) or no idursulfase-IT treatment (n = 15) for 52 weeks. All patients continued to receive weekly intravenous idursulfase 0.5 mg/kg as standard of care. Of 49 randomized patients, 47 completed the study (two patients receiving idursulfase-IT discontinued). The primary endpoint (change from baseline in DAS-II GCA score at week 52 in a linear mixed-effects model for repeated measures analysis) was not met: although there was a smaller decrease in DAS-II GCA scores with idursulfase-IT than with no idursulfase-IT at week 52, this was not significant (least-squares mean treatment difference [95% confidence interval], 3.0 [-7.3, 13.3]; p = 0.5669). Changes from baseline in Vineland Adaptive Behavioral Scales-II Adaptive Behavior Composite scores at week 52 (key secondary endpoint) were similar in the idursulfase-IT (n = 31) and no idursulfase-IT (n = 14) groups. There were trends towards a potential positive effect of idursulfase-IT across DAS-II composite, cluster, and subtest scores, notably in patients younger than 6 years at baseline. In a post hoc analysis, there was a significant (p = 0.0174), clinically meaningful difference in change from baseline in DAS-II GCA scores at week 52 with idursulfase-IT (n = 13) versus no idursulfase-IT (n = 6) among those younger than 6 years with missense iduronate-2-sulfatase gene variants. Overall, idursulfase-IT reduced cerebrospinal glycosaminoglycan levels from baseline by 72.0% at week 52. Idursulfase-IT was generally well tolerated. These data suggest potential benefits of idursulfase-IT in the treatment of cognitive impairment in some patients with neuronopathic MPS II. After many years of extensive review and regulatory discussions, the data were found to be insufficient to meet the evidentiary standard to support regulatory filings.

Efficacy of early haematopoietic stem cell transplantation versus enzyme replacement therapy on neurological progression in severe Hunter syndrome: Case report of siblings and literature review

Hunter syndrome is a neurodegenerative lysosomal storage disorder with limited treatment options to halt the progressive neurocognitive decline. Whilst Intravenous enzyme replacement therapy (ERT) does not cross the blood brain barrier; Intrathecal ERT, in clinical studies, did not demonstrate significant effect on cognition, despite having better CNS delivery. Hematopoietic stem cell transplantation (HSCT) has the potential to treat CNS disease. We reviewed the literature and outline our experience of treating two siblings with severe Hunter syndrome: ‘Sibling A' with intravenous and intrathecal ERT and ‘Sibling B' with Early HSCT. A literature review identified 8 articles reporting on the comparative efficacy of both treatments. Our clinical outcomes indicate that Sibling B performed better than Sibling A in relation to early developmental milestones as well as neurocognition, activities of daily living, quality of life and neurophysiological outcomes in mid childhood. Sibling A's developmental trajectory fell within the extremely low range and Sibling B's development trajectory fell within the low-average to average range. This suggests HSCT had a disease modifying effect and highlights the efficacy of early HSCT in moderating the CNS progression in Hunter syndrome. Long term follow up is needed to elucidate the efficacy of HSCT on neurological progression.

Analysis of cognitive ability and adaptive behavior assessment tools used in an observational study of patients with mucopolysaccharidosis II

Background

Mucopolysaccharidosis II (MPS II) is a rare lysosomal storage disease characterized by cognitive impairment in most patients. This post hoc analysis evaluated changes in cognitive function, adaptive behavior and functional outcomes in patients with neuronopathic MPS II over time. Fifty-five children with MPS II were enrolled in a 24-month observational study (NCT01822184). The Differential Ability Scales, second edition (DAS-II; early years battery for ages 2 years 6 months to 6 years 11 months, school age battery for ages 7 years to 17 years 11 months), Vineland Adaptive Behavior Scales, second edition (VABS-II) and the Hunter Syndrome-Functional Outcomes for Clinical Understanding Scale (HS-FOCUS) were performed at baseline and 3-month intervals over 2 years. A subgroup of 38 children with a DAS-II General Conceptual Ability (GCA) score of 55–85 (below average–very low abilities) at any time during the study were included in this analysis.

Results

Mean (standard deviation [SD]) early years DAS-II GCA score decreased from 73.4 (15.7, n = 22) at baseline to 62.7 (34.9, n = 6) at month 24. For the six patients with early years GCA assessments at baseline and month 24, mean (SD) GCA scores decreased from 72.3 (21.3) at baseline to 62.7 (34.9) at month 24. School age GCA scores were stable over 2 years: mean (SD) 72.4 (11.8, n = 10) at baseline; 74.3 (12.3, n = 8) at month 24. Mean (SD) VABS-II Adaptive Behavior Composite (ABC) scores were stable throughout the study (baseline, 81.8 [11.8, n = 36]; month 24, 81.0 [10.2, n = 13]). Some associations between items and domains of HS-FOCUS (p < 0.05) and DAS-II GCA and VABS-II ABC scores were shown, but there was no clear pattern of changes in HS-FOCUS over 2 years.

Conclusions

The DAS-II measured changes in cognitive function over 2 years in younger patients with MPS II, whereas cognitive function in older patients remained stable. Further research is required to confirm the content validity of the DAS-II in different patient populations with MPS II. The VABS-II and HS-FOCUS were not sensitive tools for measuring behavioral and functional changes over 2 years. These findings may inform selection of appropriate cognitive and behavioral assessment tools for future studies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-02118-3.

Evaluation of the long-term treatment effects of intravenous idursulfase in patients with mucopolysaccharidosis II (MPS II) using statistical modeling: data from the Hunter Outcome Survey (HOS)

BACKGROUND

Mucopolysaccharidosis II (MPS II; Hunter syndrome) is a rare, life-limiting lysosomal storage disease caused by deficient iduronate-2-sulfatase activity. Enzyme replacement therapy (ERT) with intravenous (IV) idursulfase can stabilize or improve many somatic manifestations, but there remains a need for further analysis of long-term treatment outcomes. Using data from patients with MPS II enrolled in the Hunter Outcome Survey (HOS), mixed modeling was performed to evaluate and predict the effects of IV idursulfase treatment on selected clinical parameters for up to 8 years following treatment start. The modeling population comprised male patients followed prospectively in HOS who had received IV idursulfase for at least 5 years and who had data available for two or more time points (at least one post-ERT). Age at ERT start and time since ERT start were included as covariates.

RESULTS

In total, 481 patients were eligible for inclusion in at least one model. At 8 years post-ERT start, improvement from baseline was predicted for each age group (< 18 months, 18 months to < 5 years and ≥ 5 years at treatment start) in the following parameters: mean urinary glycosaminoglycan levels (percentage changes of > -75% in each group), mean left ventricular mass index (decreases of ~ 1 g/m2) and mean palpable liver size (decreases of > 2 cm). Improvements in mean 6-min walk test distance (increase of > 50 m) and stabilization in percent predicted forced vital capacity and forced expiratory volume in 1 s (decreases of ~ 4 and ~ 9 percentage points, respectively) at 8 years post-ERT start were predicted for patients aged ≥ 5 years at ERT start (these assessments are unsuitable for patients aged < 5 years). Predicted changes over time were similar across the three age groups; however, overall outcomes were most favorable in children aged < 18 months at ERT start.

CONCLUSIONS

These findings suggest that the previously reported positive effects of IV idursulfase on the somatic manifestations of MPS II are predicted to be maintained for at least 8 years following ERT initiation and highlight the value of statistical modeling to predict long-term treatment outcomes in patients with rare diseases.

Natural progression of cardiac features and long-term effects of enzyme replacement therapy in Taiwanese patients with mucopolysaccharidosis II

Background

Cardiac abnormalities have been observed in patients with mucopolysaccharidosis type II (MPS II). The aim of this study was to investigate the cardiac features and natural progression of Taiwanese patients with MPS II, and evaluate the impact of enzyme replacement therapy (ERT) on cardiac structure and function.

Methods

The medical records and echocardiograms of 48 Taiwanese patients with MPS II (median age, 6.9 years; age range, 0.1–27.9 years) were reviewed. The relationships between age and each echocardiographic parameter were analyzed.

Results

The mean z-scores of left ventricular mass index (LVMI), interventricular septum diameter in diastole (IVSd), left ventricular posterior wall diameter in diastole (LVPWd), and aortic diameter were 1.10, 2.70, 0.95 and 1.91, respectively. Z scores > 2 were identified in 33%, 54%, 13%, and 46% for LVMI, IVSd, LVPWd, and aortic diameter, respectively. The most prevalent cardiac valve abnormality was mitral regurgitation (MR) (56%), followed by aortic regurgitation (AR) (33%). The severity of mitral stenosis (MS), MR, aortic stenosis (AS), AR, and the existence of valvular heart disease were all positively correlated with increasing age (p < 0.01). We also compared the echocardiographic parameters between two groups: (1) 12 patients who had up to 17 years of follow-up echocardiographic data without ERT, and (2) nine patients who had up to 12 years of follow-up data with ERT. The results showed that z-score changes of LVMI significantly improved in the patients who received ERT compared to those who did not receive ERT (0.05 versus 1.52, p < 0.05). However, the severity score changes of MS, MR, AS, and AR all showed gradual progression in both groups (p > 0.05).

Conclusions

High prevalence rates of valvular heart disease and cardiac hypertrophy were observed in the MPS II patients in this study. The existence and severity of cardiac hypertrophy and valvular heart disease in these patients worsened with increasing age, reinforcing the concept of the progressive nature of this disease. ERT for MPS II appeared to be effective in stabilizing or reducing the progression of cardiac hypertrophy, but it only had a limited effect on valvulopathy.

Enzyme replacement therapy for the treatment of Hunter disease: A systematic review with narrative synthesis and meta-analysis

BACKGROUND

In the last 10 years enzyme replacement therapy (ERT) has become an alternative for the treatment of patients with Hunter disease (HD). Nevertheless, the information regarding efficacy and safety is scarce and mainly based on the pivotal trials. This scarcity is especially evident for adults and severe forms of HD.

METHODS

A systematic review of publications in the electronic databases PUBMED, EMBASE and Cochrane Central was undertaken. Clinical trials and observational studies were included. The data about efficacy and security were retrieved and analysed with Review Manager version 5.3.

RESULTS

677 records were found, 559 remaining after the removal of duplicates. By title and abstract review, 427 were excluded. Full reading of the rest was made (122 publications) and 42 were finally included. It was not possible to perform meta-analysis of all the endpoints due to high heterogeneity in the reporting and measuring of variables in each publication. Eight clinical trials were included, 6 with high risk of bias. The quality of the other studies was low in 12%, average in 68% and good in 21%. Main findings were: a reduction in the elimination of glycosaminoglycans (GAG) in urine in all the studies (26/26), decrease in liver and spleen size (18/18), increase of 52.59 m (95% CI, 36, 42-68.76, p < .001) in the 6-min walk test (TM6M), increase in forced vital capacity (FVC) of 9.59% (95% CI 4.77-14.51, p < .001), reduction of the left ventricular mass index of 3.57% (95% CI 1.2-5.93) and reduction in mortality (OR) of 0.44 (0.27-0.71).

DISCUSSION

The data suggests a clear and consistent effect of ERT in HD reducing the accumulation of GAGs in the body, demonstrated by the reduction of its urinary excretion, as well as by the reduction of its deposits (spleen, liver and heart). Likewise, there is an improvement in physical and respiratory function. In addition, a reduction in mortality has been observed. Lack of studies, small size of the samples, and methodological deficiencies are the main limitations to establish definite conclusions.

CONCLUSIONS

The data suggests that ERT is effective and safe in the treatment of HD. There is a need to evaluate patient-centred outcomes and the impact on quality of life.

Enzyme Replacement Therapy Decreases Left Ventricular Mass Index in Patients with Hunter Syndrome?

Although enzyme replacement therapy (ERT) has shown benefit in improving cardiac systolic function in a murine model of cardiomyopathy associated with Hunter syndrome, few studies have analyzed its effect in humans. We evaluated the effect of ERT on patients with Hunter syndrome-related cardiomyopathy. We performed a retrospective analysis of serial transthoracic echocardiograms performed before and over the first 5 years after treatment initiation, in 14 patients with Hunter syndrome. An important cardiac remodeling occurred in all patients in this study. There was a significant reduction in left ventricular mass index from 70.88 to 26.75 g/m^2.7 (p = 0.003), with a trend towards a decrease in relative wall thickness from 0.515 at baseline to 0.370 after 5 years of enzyme therapy (p = 0.140). No differences were observed in aortic root diameter, left atrial diameter, left ventricular diastolic and systolic diameters, left ventricular ejection fraction, or myocardial performance index. Our findings demonstrate that ERT contributes to reducing left ventricular mass index in patients with Hunter syndrome.

Ten years of enzyme replacement therapy in paediatric onset mucopolysaccharidosis II in England

The outcome of 110 patients with paediatric onset mucopolysaccharidosis II (MPS II) since the commercial introduction of enzyme replacement therapy (ERT) in England in 2007 is reported. Median length of follow up was 10 years 3 months (range = 1 y 2 m to 18 years 6 month). 78 patients were treated with ERT, 18 had no ERT or disease modifying treatment 7 had haematopoietic stem cell transplant, 4 experimental intrathecal therapy and 3 were lost to follow up. There is clear evidence of improved survival (median age of death of ERT treated (n = 16) = 15.13 years (range = 9.53 to 20.58 y), and untreated (n = 17) = 11.43 y (0.5 to 19.13 y) p = .0005). Early introduction of ERT improved respiratory outcome at 16 years, the median FVC (% predicted) of those in whom ERT initiated <8 years = 69% (range = 34-86%) and 48% (25-108) (p = .045) in those started >8 years. However, ERT appears to have minimal impact on hearing, carpal tunnel syndrome or progression of cardiac valvular disease. Cardiac valvular disease occurred in 18/46 (40%), with progression occurring most frequently in the aortic valve 13/46 (28%). The lack of requirement for neurosurgical intervention in the first 8 years of life suggests that targeted imaging based on clinical symptomology would be safe in this age group after baseline assessments. There is also emerging evidence that the neurological phenotype is more nuanced than the previously recognized dichotomy of severe and attenuated phenotypes in patients presenting in early childhood.

The nature and impact of neurobehavioral symptoms in neuronopathic Hunter syndrome

In neuronopathic Hunter syndrome, neurobehavioral symptoms are known to be serious but have been incompletely described. While families face significant stress stemming from this complex and far-reaching array of symptoms, neither caregiver burden nor the neurobehavioral symptoms have been measured comprehensively. We delineated these neurobehavioral characteristics and their impact on the caregiver using multiple approaches. Methods: As part of the initial phase of developing a Hunter-specific behavioral assessment tool, we used multiple methods to obtain data on patient behaviors and caregiver burden, with the intention of drafting item sets for the tool. We utilized 1) caregiver descriptions from focus groups and individual interviews, 2) observations from video-recorded play of affected children, 3) descriptions from historic chart review, 4) consultation with patient advocacy groups and international experts, 5) reports from a caregiver advisory board, and 6) literature review. Results: Neurobehavioral symptoms were diverse and categorized as focus/attention, impulsivity/heightened activity, sensation seeking, emotional/behavioral function, social interaction, and sleep. A significant reported challenge was susceptibility to misinterpretation of some behaviors as defiant or aggressive, particularly if physical. Caregiver burden involved social isolation, exhaustion, stress, and financial and vocational strain. These new descriptions will aid in developing quantitative measures of change in neurobehavioral symptoms and family burden. These descriptions will be the foundation of a neurobehavioral rating scale, which is very much needed to aid in patient management and assess interventions for individuals with neuronopathic Hunter syndrome.

Cochlear Implantation via the Transmeatal Approach in an Adolescent with Hunter Syndrome-Type II Mucopolysaccharidosis

Type II mucopolysaccharidosis (MPS II) commonly known as Hunter syndrome, is a rare X-linked lysosomal storage disorder caused by iduronate-2-sulfatase deficiency, which in turn causes otorhinolaryngological manifestations, including sensorineural hearing loss (SNHL). Previously, the median survival age of patients with MPS was approximately 13.4 years. However, in the era of enzyme replacement therapy and other multidisciplinary care modalities, the life expectancy has increased. Herein, we report a rare case of an adolescent with MPS II who underwent SNHL treatment with cochlear implantation (CI). Based on unexpected findings of mastoid emissary veins and overgrowth of the vessels around the temporal bone, CI was performed using the transmeatal approach instead of the conventional transmastoid method, to avoid damage to the vessels. The average hearing threshold after CI was 35 dB and no surgical complications were encountered. Adolescent MPS II may present vessel abnormalities, which can reduce the success rate of surgery. In patients with MPS II with SNHL, CI should be performed under careful monitoring of vessel overgrowth. Moreover, with regard to feasibility of CI in adolescent patients with MPS II with SNHL, surgical techniques such as the transmeatal approach should be selected based on adequate assessment of the case.

Modelling the neuropathology of lysosomal storage disorders through disease-specific human induced pluripotent stem cells

Mucopolysaccharidosis II (MPS II) is a lysosomal storage disorder (LSD), caused by iduronate 2-sulphatase (IDS) enzyme dysfunction. The neuropathology of the disease is not well understood, although the neural symptoms are currently incurable. MPS II-patient derived iPSC lines were established and differentiated to neuronal lineage. The disease phenotype was confirmed by IDS enzyme and glycosaminoglycan assay. MPS II neuronal precursor cells (NPCs) showed significantly decreased self-renewal capacity, while their cortical neuronal differentiation potential was not affected. Major structural alterations in the ER and Golgi complex, accumulation of storage vacuoles, and increased apoptosis were observed both at protein expression and ultrastructural level in the MPS II neuronal cells, which was more pronounced in GFAP + astrocytes, with increased LAMP2 expression but unchanged in their RAB7 compartment. Based on these finding we hypothesize that lysosomal membrane protein (LMP) carrier vesicles have an initiating role in the formation of storage vacuoles leading to impaired lysosomal function. In conclusion, a novel human MPS II disease model was established for the first time which recapitulates the in vitro neuropathology of the disorder, providing novel information on the disease mechanism which allows better understanding of further lysosomal storage disorders and facilitates drug testing and gene therapy approaches.

Aversive and non-aversive memory impairment in the mucopolysaccharidosis II mouse model

Hunter syndrome (MPS II, OMIM 309900) is a lysosomal storage disorder due to deficient iduronate sulphatase activity. Patients present multiple cognitive alterations, and the aim of this work was to verify if MPS II mice also present some progressive cognitive alterations. For that, MPS II mice from 2 to 6 months of age were submitted to repeated open field and inhibitory avoidance tests to evaluate memory parameters. MPS II mice presented impaired memory at 6 months evaluated by open field test. They also performed poorly in the inhibitory avoidance test from 4 months. We conclude that MPS II mice develop cognitive alterations as the disease progresses. These tests can be used in the future to study the efficacy of therapeutic approaches in the central nervous system.

Correlation between urinary GAG and anti-idursulfase ERT neutralizing antibodies during treatment with NICIT immune tolerance regimen: A case report

INTRODUCTION

Antibodies to intravenous idursulfase enzyme replacement therapy (ERT) for patients with Hunter syndrome (mucopolysaccharidosis type II, MPS II) can have a harmful clinical impact, including both increasing risk of infusion reactions and inhibiting therapeutic activity. Thus, failure to monitor anti-idursulfase antibodies and neutralizing antibodies, and delays in reporting results, may postpone critical clinical decisions.

HYPOTHESIS

Urinary glycosaminoglycan (GAG) levels may be used as a biomarker for anti-idursulfase antibodies and neutralizing antibodies to improve timeliness in monitoring and managing ERT.

METHODS

This is a case report describing a patient with MPS II with high levels of neutralizing antibodies and worsened clinical status who was treated for five years with a non-immunosuppressive and non-cytotoxic immune tolerance (NICIT) regimen, consisting of intravenous immune globulin and frequent infusions of idursulfase. Neutralizing antibodies and total anti-idursulfase antibodies were measured by two different methods, the direct 1,9-dimethylmethylene blue (DMB) assay and cetylpyridinium chloride carbazole-borate (CPC) assay.

RESULTS

Neutralizing antibodies, measured as percent inhibition of enzyme activity and also by total neutralizing antibody titer, were correlated with quantitative urinary GAG measured by DMB assay (p=0.026, p=0.0067), and quantitative urinary GAG by CPC assay with percent inhibition of enzyme activity by neutralizing antibodies (p=0.0475). The NICIT regimen showed a sustained immune tolerance after five years and was well-tolerated.

CONCLUSIONS

Urinary GAG, measured by DMB assay, may be a biomarker for anti-idursulfase neutralizing antibodies and is useful for managing immune tolerance regimens for patients with MPS II who have high levels of anti-idursulfase neutralizing antibodies. This study highlights the importance of regular and frequent monitoring of urinary GAG in patients with MPS II who are receiving ERT. The NICIT regimen, with less drug toxicities, may be preferred in patients with MPS who have a high risk of infections and whose disease progresses less rapidly than some other lysosomal storage diseases, such as infantile Pompe disease.

Synchrotron X-ray diffraction to understand crystallographic texture of enamel affected by Hunter syndrome

OBJECTIVE

To determine whether Hunter syndrome (MPS II) affects the crystallographic texture (preferred orientation) of enamel.

DESIGN

Synchrotron X-ray diffraction, being a state of the art technique, has been used to determine the enamel crystallite orientation in enamel affected by Hunter syndrome (MPS II). The incisal, lingual and cervical regions of the MPS II affected tooth were observed and compared to healthy tooth.

RESULTS

It was observed that there is a loss of organization of crystallites in deciduous incisal enamel affected by Hunter syndrome (MPS II) as compared to healthy deciduous enamel tissue. Generally it was observed that, in contrast to the healthy enamel, the enamel affected by MPS II possessed a lower crystallographic preferred orientation, with a more uniform spatial distribution; however, the enamel at the incisal tip was relatively unaffected.

CONCLUSION

Hunter syndrome affects the enamel texture in the lingual and cervical regions of the tooth.

Hematopoietic Stem Cell Transplantation for Patients with Mucopolysaccharidosis II

There is limited information regarding the long-term outcomes of hematopoietic stem cell transplantation (HSCT) for mucopolysaccharidosis II (MPS II). In this study, clinical, biochemical, and radiologic findings were assessed in patients who underwent HSCT and/or enzyme replacement therapy (ERT). Demographic data for 146 HSCT patients were collected from 27 new cases and 119 published cases and were compared with 51 ERT and 15 untreated cases. Glycosaminoglycan (GAG) levels were analyzed by liquid chromatography tandem mass spectrometry in blood samples from HSCT, ERT, and untreated patients as well as age-matched controls. Long-term magnetic resonance imaging (MRI) findings were investigated in 13 treated patients (6 ERT and 7 HSCT). Mean age at HSCT was 5.5 years (range, 2 to 21.4 years) in new patients and 5.5 years (range, 10 months to 19.8 years) in published cases. None of the 27 new patients died as a direct result of the HSCT procedure. Graft-versus-host disease occurred in 8 (9%) out of 85 published cases, and 9 (8%) patients died from transplantation-associated complications. Most HSCT patients showed greater improvement in somatic features, joint movements, and activity of daily living than the ERT patients. GAG levels in blood were significantly reduced by ERT and levels were even lower after HSCT. HSCT patients showed either improvement or no progression of abnormal findings in brain MRI while abnormal findings became more extensive after ERT. HSCT seems to be more effective than ERT for MPS II in a wide range of disease manifestations and could be considered as a treatment option for this condition.

Multi-criteria decision analysis (MCDA): testing a proposed MCDA framework for orphan drugs

Background

Since the introduction of the orphan drugs legislation in Europe, it has been suggested that the general method of assessing drugs for reimbursement is not necessarily suitable for orphan drugs. The National Institute for Health and Clinical Excellence indicated that several criteria other than cost and efficacy could be considered in reimbursement decisions for orphan drugs. This study sought to explore the multi-criteria decision analysis (MCDA) framework proposed by (Orphanet J Rare Dis 7:74, 2012) to a range of orphan drugs, with a view to comparing the aggregate scores to the average annual cost per patient for each product, and thus establishing the merit of MCDA as a tool for assessing the value of orphan drugs in relation to their pricings.

Methods

An MCDA framework was developed using the nine criteria proposed by (Orphanet J Rare Dis 7:74, 2012) for the evaluation of orphan drugs, using the suggested numerical scoring system on a scale of 1 to 3 for each criterion. Correlations between the average annual cost of the drugs and aggregate MCDA scores were tested and plotted graphically. Different weightings for each of the attributes were also tested. A further analysis was conducted to test the impact of including the drug cost as an attribute in the aggregate index scores.

Results

In the drugs studied, the R², that statistically measures how close the data are to the fitted regression line was 0.79 suggesting a strong correlation between the drug scores and the average annual cost per patient.

Conclusion

Despite several limitations of the proposed model, this quantitative study provided insight into using MCDA and its relationship to the average annual costs of the products.

Causes of death and clinical characteristics of 34 patients with Mucopolysaccharidosis II in Taiwan from 1995-2012

BACKGROUND

Mucopolysaccharidosis type II (MPS II) is an X-linked recessive, multisystemic lysosomal storage disorder caused by a deficiency of iduronate-2-sulfatase. MPS II has a variable age of onset and variable rate of progression. In Asian countries, there is a relatively higher incidence of MPS II compared to other types of MPS.

METHODS

A retrospective analysis was carried out of 34 Taiwanese MPS II patients who died between 1995 and 2012. The clinical characteristics, medical records, age at death, and cause of death were evaluated to better understand the natural progression of this disease.

RESULTS

The mean age at death of 31 of the patients with a severe form of the disease with significant cognitive impairment was 13.2 ± 3.2 years, compared with 22.6 ± 4.3 years in the three patients with a mild form of the disease without cognitive involvement (n = 2) or the intermediate form (n = 1) (p < 0.001). The mean ages at onset of symptoms and confirmed diagnosis were 2.5 ± 2.1 and 4.8 ± 3.1 years, respectively (n = 32). Respiratory failure was the leading cause of death (56 %), followed by cardiac failure (18 %), post-traumatic organ failure (3 %), and infection (sepsis) (3 %) (n = 27). Age at onset of symptoms was positively correlated with life expectancy (p < 0.01). Longevity gradually increased over time from 1995 to 2012 (p < 0.05).

CONCLUSIONS

Respiratory failure and cardiac failure were the two major causes of death in these patients. The life expectancy of Taiwanese MPS II patients has improved in recent decade.

Levels of glycosaminoglycans in the cerebrospinal fluid of healthy young adults, surrogate-normal children, and Hunter syndrome patients with and without cognitive impairment

In mucopolysaccharidoses (MPS), glycosaminoglycans (GAG) accumulate in tissues. In MPS II, approximately two-thirds of patients are cognitively impaired. We investigated levels of GAG in cerebrospinal fluid (CSF) in different populations from four clinical studies (including NCT00920647 and NCT01449240). Data indicate that MPS II patients with cognitive impairment have elevated levels of CSF GAG, whereas those with the attenuated phenotype typically have levels falling between those of the cognitively affected patients and healthy controls.

Safety and efficacy of enzyme replacement therapy with idursulfase beta in children aged younger than 6 years with Hunter syndrome

Idursulfase beta (Hunterase®) has been used for enzyme replacement therapy (ERT) of patients with mucopolysaccharidosis II (MPS II, Hunter syndrome) aged 6 years or older since 2012 in Korea. The objective of this study was to evaluate the safety and efficacy of ERT with idursulfase beta in Hunter syndrome children younger than 6 years. This study was a 52-week, single center, single arm, open-label clinical trial (NCT01645189). Idursulfase beta (0.5mg/kg/week) was administered intravenously for 52 weeks. The primary endpoint was safety assessed by adverse events (AEs). Secondary endpoints included vital signs, physical examination, ECG, laboratory tests, anti-idursulfase antibodies, and efficacy represented by changes in urinary glycosaminoglycan (GAG) at week 53 from baseline. In addition, growth indices and developmental milestones (Denver II test) were evaluated as exploratory variables. All six patients experienced at least one AE. A total of 109 AEs were reported. One patient experienced a serious AE (hospitalization due to gastroenteritis) that was considered not to be treatment related. One patient (16.7%) experienced infusion-related adverse drug reactions (ADRs), developing urticaria six times and a cough five times. There were no serious ADRs and no clinically significant changes in vital signs, physical exam, laboratory parameters, or ECG. Of the six patients, four (66.7%) showed anti-idursulfase antibodies and neutralizing antibodies on at least one occasion during the study. At week 53, urinary GAG was significantly reduced by -35.1±30.6mgGAG/g creatine from baseline (P=0.038). This study indicates that the safety and efficacy of idursulfase beta are similar to those reported in Hunter syndrome patients aged 6 years or older.

Brazilian reference values for MPS II screening in dried blood spots--a fluorimetric assay

OBJECTIVES

Mucopolysaccharidosis II (MPS II), or Hunter Syndrome, is a lysosomal storage disorder that is caused by the deficiency or absence of iduronate-2-sulfatase (IDS) enzyme; in this disease, early diagnosis is essential to provide higher life expectancy for patients. This study validates a fluorimetric assay that is used to assess IDS enzyme activity using dried blood spot (DBS) samples and presents the reference interval for the Brazilian population.

DESIGN AND METHODS

Venous blood sample was collected in heparin tubes for leukocyte extraction and DBS preparation. IDS activity in the leukocytes was analyzed, and the results were considered the gold standard reference for the categorization of volunteers as positive or negative controls (PC and NC, respectively). IDS activity in the DBS was analyzed using an adapted version of the leukocyte assay. Statistical analyses were performed using a ROC curve to determine cutoff values and using a parametric Student's t test to compare values between genders. To verify that the assay yielded consistent results, a Bland-Altman plot was prepared.

RESULTS

Leukocyte IDS activity values ranged between 2.71 and 17.36 nmol/mg protein/h in the NC group and between 0 and 0.11 nmol/mg protein/h in the PC group. Based on the DBS assay, activities ranged between 1.83 and 16.86 μmol/L blood/h in the NC group and between 0.58 and 4.32 μmol/L blood/h in the PC group.

CONCLUSIONS

Reference values of IDS activity were determined in DBS with acceptable sensitivity and specificity. Therefore, the DBS assay described in this work may be a useful tool to screen MPS II patients in the Brazilian population.

Increased incidence of neonatal respiratory distress in infants with mucopolysaccharidosis type II (MPS II, Hunter syndrome)

Records were reviewed on all patients with mucopolysaccharidosis type II (Hunter syndrome) seen at a single institution from 1999 to 2013 to identify those with a history of neonatal intensive care. Eleven of 34 patients were in a neonatal intensive care unit and all had respiratory distress with 8 diagnoses of respiratory distress syndrome and 3 of transient tachypnea of the newborn. None of the infants were premature; four were delivered by cesarean section. These findings suggest that respiratory distress is more commonly observed in neonates with MPS II than in the general population. This may reflect airway disease already present in this disorder at the time of birth.

Impact of enzyme replacement therapy on linear growth in Korean patients with mucopolysaccharidosis type II (Hunter syndrome)

Hunter syndrome (or mucopolysaccharidosis type II [MPS II]) arises because of a deficiency in the lysosomal enzyme iduronate-2-sulfatase. Short stature is a prominent and consistent feature in MPS II. Enzyme replacement therapy (ERT) with idursulfase (Elaprase®) or idursulfase beta (Hunterase®) have been developed for these patients. The effect of ERT on the growth of Korean patients with Hunter syndrome was evaluated at a single center. This study comprised 32 patients, who had received ERT for at least 2 yr; they were divided into three groups according to their ages at the start of ERT: group 1 (<6 yr, n=14), group 2 (6-10 yr, n=11), and group 3 (10-20 yr, n=7). The patients showed marked growth retardation as they got older. ERT may have less effect on the growth of patients with the severe form of Hunter syndrome. The height z-scores in groups 2 and 3 revealed a significant change (the estimated slopes before and after the treatment were -0.047 and -0.007, respectively: difference in the slope, 0.04; P<0.001). Growth in response to ERT could be an important treatment outcome or an endpoint for future studies.

The relationship between anti-idursulfase antibody status and safety and efficacy outcomes in attenuated mucopolysaccharidosis II patients aged 5 years and older treated with intravenous idursulfase

In the pivotal phase II/III trial of idursulfase administered intravenously to treat mucopolysaccharidosis II, approximately half of the patients developed antibodies to idursulfase. This post-hoc analysis of data from the phase II/III trial and extension study examined the relationship between antibody status and outcomes. A total of 63 treatment-naïve patients received 0.5 mg/kg of intravenous idursulfase weekly for two years. Thirty-two patients (51%) were positive for anti-idursulfase IgG antibodies, 23 of whom (37%) became persistently positive. All patients who developed an antibody response did so by their scheduled Week 27 study visit. Positive antibody status appeared to have no statistically significant effect upon changes in six-minute walk test distance, percent predicted forced vital capacity, or liver and spleen volume. All patients showed significant decreases in urinary GAG levels, although the antibody positive group maintained somewhat higher urinary GAG levels than their antibody-negative counterparts at the end of study (138.7 vs. 94.7 μg/mg creatinine, p = 0.001). Antibody positivity was not associated with a higher event rate for serious adverse events. Among patients who had no prior infusion-related reactions, antibody positive patients were 2.3 times more likely to have a first infusion-related reaction than those who would remain negative (p = 0.017); the risk increased to 2.5 times more likely for those who were persistently positive (p = 0.009). These differences in risk disappeared among patients with a previous infusion-related reaction, likely because of preventive measures. A genotype analysis for the 36 patients with available data found that patients with nonsense or frameshift mutations may be more likely to develop antibodies, to experience infusion-related reactions, and to have a reduced uGAG response than those with missense mutations, suggesting the possibility that antibodies are not a driver of clinical outcomes but rather a marker for genotype.

A study of the relationship between clinical phenotypes and plasma iduronate-2-sulfatase enzyme activities in Hunter syndrome patients

Purpose

Mucopolysaccharidosis type II (MPS II or Hunter syndrome) is a rare lysosomal storage disorder caused by iduronate-2-sulfatase (IDS) deficiency. MPS II causes a wide phenotypic spectrum of symptoms ranging from mild to severe. IDS activity, which is measured in leukocyte pellets or fibroblasts, was reported to be related to clinical phenotype by Sukegawa-Hayasaka et al. Measurement of residual plasma IDS activity using a fluorometric assay is simpler than conventional measurements using skin fibroblasts or peripheral blood mononuclear cells. This is the first study to describe the relationship between plasma IDS activity and clinical phenotype of MPS II.

Methods

We hypothesized that residual plasma IDS activity is related to clinical phenotype. We classified 43 Hunter syndrome patients as having attenuated or severe disease types based on clinical characteristics, especially intellectual and cognitive status. There were 27 patients with the severe type and 16 with the attenuated type. Plasma IDS activity was measured by a fluorometric enzyme assay using 4-methylumbelliferyl-α-iduronate 2-sulphate.

Results

Plasma IDS activity in patients with the severe type was significantly lower than that in patients with the attenuated type (P=0.006). The optimal cut-off value of plasma IDS activity for distinguishing the severe type from the attenuated type was 0.63 nmol·4 hr^-1·mL^-1. This value had 88.2% sensitivity, 65.4% specificity, and an area under receiver-operator characteristics (ROC) curve of 0.768 (ROC curve analysis; P=0.003).

Conclusion

These results show that the mild phenotype may be related to residual lysosomal enzyme activity.