Cognitive and adaptive measurement endpoints for clinical trials in mucopolysaccharidoses types I, II, and III: A review of the literature

[Formula: see text] Neuropsychological assessment in rare pediatric neurogenetic disorders: considerations for cross-cultural clinical research

Neuropsychological assessment in rare neurodevelopmental disorders has provided clinicians and researchers with a more comprehensive view of natural history as well as opportunities for additional endpoints in treatment trials. While challenges to protocol development have been addressed in the literature, cultural considerations have been overly broad resulting in limited utility when including mixed international samples. Using experiences over the past five years with the development of ten different protocols for neurogenetic rare diseases, this paper presents further considerations for protocol development that are culturally sensitive to international samples. Recommendations are offered across areas including participants from multiple countries; cognitive, sensory and motor impairments; psychometrics; and assessment logistics. A neuropsychological assessment selection checklist that guides researchers and clinicians through considerations and a standard operating procedure that provides guidance on thinking through the assessment process are offered.

Neuropsychology assessment and outcomes in adult mucopolysaccharidosis - A systematic review as the first step to service development in a large tertiary Lysosomal Storage Disorders centre

A systematic review of Randomised Controlled Trials in adult mucopolysaccharidoses (MPSs) was conducted to inform neuropsychology service development at a large tertiary Lysosomal Storage Diseases centre. Studies including psychological endpoints for cognition, mood, and quality of life were reviewed. Forty-eight studies met the inclusion criteria for full text review. Of the 48 studies, 44% (21/48) included adult participants, while psychological endpoints were used in 52% (25/48) for cognition, 11% (5/48) for mood, and 69% (33/48) for quality of life. Five studies included both adult participants and relevant psychological endpoints. Risk of bias ratings were 'high' for two studies, while two studies received a rating of 'some concerns', and the last study a 'low' risk of bias rating. The evidence base for psychological outcomes in adult MPS disorders is limited and insufficient for guiding neuropsychology service development. Data on the psychosocial effects of MPS across the lifespan will be crucial for planning service development and supporting the neuropsychological needs of adult patients and their families.

Sanfilippo syndrome: consensus guidelines for clinical care

Sanfilippo syndrome is a group of rare, complex, and progressive neurodegenerative lysosomal storage disorders that is characterized by childhood dementia. The clinical management of patients with progressive neurological decline and multisystem involvement requires a multidisciplinary team with experience in the management of neurodegenerative disorders. Best practice guidelines for the clinical management of patients with these types of rare disorders are critical to ensure prompt diagnosis and initiation of appropriate care. However, there are no published standard global clinical care guidelines for patients with Sanfilippo syndrome. To address this, a literature review was conducted to evaluate the current evidence base and to identify evidence gaps. The findings were reviewed by an international steering committee composed of clinical experts with extensive experience in managing patients with Sanfilippo syndrome. The goal was to create a consensus set of basic clinical guidelines that will be accessible to and informed by clinicians globally, as well as providing a practical resource for families to share with their local care team who may not have experience with this rare disease. This review distills 178 guideline statements into an easily digestible document that provides evidence-based, expert-led recommendations for how to approach common management challenges and appropriate monitoring schedules in the care of patients with Sanfilippo syndrome.

Quantifying medical manifestations in Hurler syndrome with the infant physical symptom score: associations with long-term physical and adaptive outcomes

BACKGROUND

A physical symptom score (PSS) for the mucopolysaccharidosis (MPS) disorders has been developed to quantitate the somatic burden of disease across multiple organ systems. Studies have demonstrated the sensitivity and its relationship to age, IQ and adaptive functioning of the PSS in older children. With the onset of newborn screening, there is an increased need to characterize the somatic symptoms in the earliest stages of life, especially for young children under 36 months of age. Consequently, a new scale, Infant Physical Symptom Score (IPSS), was developed to score physical symptoms in infants and toddlers.

OBJECTIVE

Part I. To create a measure to quantify somatic burden in patients with MPS disorders under 36 months of age. The IPSS assess outcomes and changes in somatic disease in individuals with MPS disorders diagnosed very early in life. Part II. To determine the relationship between IPSS and other measures to evaluate its validity and utility, a) we evaluated the relationship between the IPSS and PSS in the same patients with MPS I over time to determine if the two scales are measuring the same concepts, and b) we evaluated the association between IPSS and a functional adaptive measure over time with a focus on the age at first treatment (under 36 months) to determine if the IPSS has predictive value.

METHODS

Part I. The Infant Physical Symptom Score (IPSS) for the infant population in MPS disorders was established using data from 39 patients enrolled in the Lysosomal Disease Network longitudinal MPS I study (U54NS065768). All of these patients had Hurler syndrome (MPS IH) and underwent hematopoietic stem cell transplant (HSCT) at the University of Minnesota. Items for the IPSS were selected by reviewing CRFs prepared for the MPS I longitudinal study and examining medical records of these patients prior to HSCT based on the knowledge gained from the development of the PSS. Part II. Of those 39 patients, a subset of 19 were all seen 9 to 12 years post HSCT. Having retrospectively calculated their IPSS prior to HSCT, we categorized them by age at HSCT, and examined their most recent PSS along with Composite and Daily Living Skills scores on the Vineland Adaptive Behavior Scales - Second Edition (VABS-II).

RESULTS AND CONCLUSION

The total score on the IPSS collected prior to transplant differed by patient's age at transplant, as expected in this progressive condition. Those transplanted at ≤12 months of age had a mean score of 7.4, which was significantly lower, suggesting less somatic disease burden, compared to those transplanted at >12 to ≤24 months (mean 11.8) and > 24 to ≤36 months (mean 13.6). Higher IPSS reflects more evidence of somatic disease burden and lower IPSS reflects less evidence of disease burden. Nine to 12 years later, the severity level as measured by the PSS was comparable to severity on the IPSS suggesting that the two scales are measuring similar concepts. Retrospectively calculated pre-transplant IPSS were negatively associated with higher VABS-II Composite scores 9-12 years later (p value-0.015) and to a lesser extent Daily Living Skills scores (p value-0.081). We conclude that the IPSS appears to be a useful approach to quantifying the somatic disease burden of MPS IH patients under 36 months of age.

Use of the Vineland-3, a measure of adaptive functioning, in CLN3

Progressive vision loss and neurocognitive impairment are early and frequent presentations in CLN3 disease. This highlights neurodevelopmental functioning as critical to the disease, but limits the neuropsychological test repertoire. We evaluated the convergent validity of the Vineland Adaptive Behavior Scales as a potential outcome measure. In a prospective observational study of 22 individuals (female:male 11:11; 6-20 years-old) with a molecular diagnosis of CLN3, we used generalized linear models and Spearman correlations to quantify the relationship of the adaptive behavior composite (ABC) standard score with established outcomes of verbal IQ (VIQ) and disease severity (Unified Batten Disease Rating Scale, UBDRS) scores. We analyzed ABC changes in 1-year follow-up data in a subset of the same cohort (n = 17). The ABC and VIQ, both standard scores, exhibited a strong positive correlation in cross-sectional data (r = 0.81). ABC and UBDRS scores were strongly and positively correlated in cross-sectional data (r_range  = 0.87-0.93). Participants' ABC scores decreased slightly over the 1-year follow-up period (mean change, 95% CI: -5.23, -2.16). The convergent validity of the Vineland-3 for use in CLN3 is supported by its relationships with the established outcomes of VIQ and UBDRS. Future longitudinal research, including replication in other cohorts and evaluation of sensitivity to change, will be important to establish utility of the Vineland-3 for monitoring change in CLN3.

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.

The natural history of neurocognition in MPS disorders: A review

MPS disorders are associated with a wide spectrum of neurocognitive effects, from mild problems with attention and executive functions to progressive and degenerative neuronopathic disease. Studies of the natural history of neurocognition are necessary to determine the profile of abnormality and the rates of change, which are crucial to select endpoints for clinical trials of brain treatments and to make clinical recommendations for interventions to improve patients' quality of life. The goal of this paper is to review neurocognitive natural history studies to determine the current state of knowledge and assist in directing future research in all MPS disorders. There are seven different types of MPS diseases, each resulting from a specific enzyme deficiency and each having a separate natural history. MPS IX, will not be discussed as there are only 4 cases reported in the literature without cognitive abnormality. For MPS IH, hematopoietic cell transplant (HCT) is standard of care and many studies have documented the relationship between age at treatment and neurocognitive outcome, and to a lesser extent, neurocognitive status at baseline. However, the mortality and morbidity associated with the transplant process and residual long-term problems after transplant, have led to renewed efforts to find better treatments. Rather than natural history, new trials will likely need to use the developmental trajectories of the patients with HCT as a comparators. The literature has extensive data regarding developmental trajectories post-HCT. For attenuated MPS I, significant neurocognitive deficits have been documented, but more longitudinal data are needed in order to support a treatment directed at their attention and executive function abnormalities. The neuronopathic form of MPS II has been a challenge due to the variability of the trajectory of the disease with differences in timing of slowing of development and decline. Finding predictors of the course of the disease has only been partially successful, using mutation type and family history. Because of lack of systematic data and clinical trials that precede a thorough understanding of the disease, there is need for a major effort to gather natural history data on the entire spectrum of MPS II. Even in the attenuated disease, attention and executive function abnormalities need documentation. Lengthy detailed longitudinal studies are needed to encompass the wide variability in MPS II. In MPS IIIA, the existence of three good natural history studies allowed a quasi-meta-analysis. In patients with a rapid form of the disease, neurocognitive development slowed up until 42 to 47 months, halted up to about 54 months, then declined rapidly thereafter, with a leveling off at an extremely low age equivalent score below 22 months starting at about chronological age of 6. Those with slower or attenuated forms have been more variable and difficult to characterize. Because of the plethora of studies in IIIA, it has been recommended that data be combined from natural history studies to minimize the burden on parents and patients. Sufficient data exists to understand the natural history of cognition in MPS IIIA. MPS IIIB is quite similar to IIIA, but more attenuated patients in that phenotype have been reported. MPS IIIC and D, because they are so rare, have little documentation of natural history despite the prospects of treatments. MPS IV and VI are the least well documented of the MPS disorders with respect to their neurocognitive natural history. Because, like attenuated MPS I and II, they do not show progression of neurocognitive abnormality and most patients function in the range of normality, their behavioral, attentional, and executive function abnormalities have been ignored to the detriment of their quality of life. A peripheral treatment for MPS VII, extremely rare even among MPS types, has recently been approved with a post-approval monitoring system to provide neurocognitive natural history data in the future. More natural history studies in the MPS forms with milder cognitive deficits (MPS I, II, IV, and VI) are recommended with the goal of improving these patients' quality of life with and without new brain treatments, beyond the benefits of available peripheral enzyme replacement therapy. Recommendations are offered at-a-glance with respect to what areas most urgently need attention to clarify neurocognitive function in all MPS types.

miR-143 Regulates Lysosomal Enzyme Transport across the Blood-Brain Barrier and Transforms CNS Treatment for Mucopolysaccharidosis Type I

During brain maturation, cation-independent mannose-6-phosphate receptor (CI-MPR), a key transporter for lysosomal hydrolases, decreases significantly on the blood-brain barrier (BBB). Such a phenomenon leads to poor brain penetration of therapeutic enzymes and subsequent failure in reversing neurological complications in patients with neuropathic lysosomal storage diseases (nLSDs), such as Hurler syndrome (severe form of mucopolysaccharidosis type I [MPS I]). In this study, we discover that upregulation of microRNA-143 (miR-143) contributes to the decline of CI-MPR on the BBB during development. Gain- and loss-of-function studies showed that miR-143 inhibits CI-MPR expression and its transport function in human endothelial cells in vitro. Genetic removal of miR-143 in MPS I mice enhances CI-MPR expression and improves enzyme transport across the BBB, leading to brain metabolic correction, pathology normalization, and correction of neurological functional deficits 5 months after peripheral protein delivery at clinically relevant levels that derived from erythroid/megakaryocytic cells via hematopoietic stem cell-mediated gene therapy, when otherwise no improvement was observed in MPS I mice at a parallel setting. These studies not only uncover a novel role of miR-143 as an important modulator for the developmental decline of CI-MPR on the BBB, but they also demonstrate the functional significance of depleting miR-143 for "rescuing" BBB-anchored CI-MPR on advancing CNS treatment for nLSDs.

The Value of Case Reports in Systematic Reviews from Rare Diseases. The Example of Enzyme Replacement Therapy (ERT) in Patients with Mucopolysaccharidosis Type II (MPS-II)

BACKGROUND

Case reports are usually excluded from systematic reviews. Patients with rare diseases are more dependent on novel individualized strategies than patients with common diseases. We reviewed and summarized the novelties reported by case reports in mucopolysaccharidosis type II (MPS-II) patients treated with enzyme replacement therapy (ERT).

METHODS

We selected the case reports included in a previous meta-analysis of patients with MPS-II treated with ERT. Later clinical studies evaluating the same topic of those case reports were reported. Our primary aim was to summarize novelties reported in previous case reports. Secondary objectives analyzed the number of novelties evaluated in subsequent clinical studies and the time elapsed between the publication of the case report to the publication of the clinical study.

RESULTS

We identified 11 innovative proposals in case reports that had not been previously considered in clinical studies. Only two (18.2%) were analyzed in subsequent nonrandomized cohort studies. The other nine novelties (81.8%) were analyzed in later case reports (five) or were not included in ulterior studies (four) after more than five years from their first publication.

CONCLUSIONS

Case reports should be included in systematic reviews of rare disease to obtain a comprehensive summary of the state of research and offer valuable information for healthcare practitioners.

Therapy development for the mucopolysaccharidoses: Updated consensus recommendations for neuropsychological endpoints

Neurological dysfunction represents a significant clinical component of many of the mucopolysaccharidoses (also known as MPS disorders). The accurate and consistent assessment of neuropsychological function is essential to gain a greater understanding of the precise natural history of these conditions and to design effective clinical trials to evaluate the impact of therapies on the brain. In 2017, an International MPS Consensus Panel published recommendations for best practice in the design and conduct of clinical studies investigating the effects of therapies on cognitive function and adaptive behavior in patients with neuronopathic mucopolysaccharidoses. Based on an International MPS Consensus Conference held in February 2020, this article provides updated consensus recommendations and expands the objectives to include approaches for assessing behavioral and social-emotional state, caregiver burden and quality of life in patients with all mucopolysaccharidoses.

Natural history of cognitive development in neuronopathic mucopolysaccharidosis type II (Hunter syndrome): Contribution of genotype to cognitive developmental course

The natural history of cognitive growth in the neuronopathic form of Mucopolysaccharidosis type II (MPS II) is not well defined especially their patterns of development and decline. The ability to predict the developmental course of the neurologically impaired patient is necessary to assess treatment outcomes aimed at the brain. Thirteen intravenous enzyme replacement therapy-treated Japanese patients with neuronopathic MPSII who had mutation analysis were followed on one standard measure of cognitive development over time. Six children in Group MS had missense mutations and 7 children in Group NT had null type mutations such as deletions, recombination with the pseudogene, and nonsense mutations. The patients as a whole demonstrated cognitive growth until about 36-42 months of age, followed by a plateau in development. The mean age equivalent score at age 3 was similar to that at age 6. While the decline was slow for the entire group, the patients in Group NT showed a more rapid decline than those in Group MS. Two patients with deletions showed decline to a very low level by age 5. The long plateau in cognitive development in patents with MPS II was substantiated and was consistent with other studies. This is the first demonstration that different mutation types within the neuronopathic MPS II patients are associated with different rates of decline. We also were able to identify the chronological age before which a trial would need to start in order to maintain cognitive growth and a ceiling beyond which a relatively normal outcome would not be likely.

Mucopolysaccharidosis Type I: A Review of the Natural History and Molecular Pathology

Mucopolysaccharidosis type I (MPS I) is a rare autosomal recessive inherited disease, caused by deficiency of the enzyme α-L-iduronidase, resulting in accumulation of the glycosaminoglycans (GAGs) dermatan and heparan sulfate in organs and tissues. If untreated, patients with the severe phenotype die within the first decade of life. Early diagnosis is crucial to prevent the development of fatal disease manifestations, prominently cardiac and respiratory disease, as well as cognitive impairment. However, the initial symptoms are nonspecific and impede early diagnosis. This review discusses common phenotypic manifestations in the order in which they develop. Similarities and differences in the three animal models for MPS I are highlighted. Earliest symptoms, which present during the first 6 months of life, include hernias, coarse facial features, recurrent rhinitis and/or upper airway obstructions in the absence of infection, and thoracolumbar kyphosis. During the next 6 months, loss of hearing, corneal clouding, and further musculoskeletal dysplasias develop. Finally, late manifestations including lower airway obstructions and cognitive decline emerge. Cardiac symptoms are common in MPS I and can develop in infancy. The underlying pathogenesis is in the intra- and extracellular accumulation of partially degraded GAGs and infiltration of cells with enlarged lysosomes causing tissue expansion and bone deformities. These interfere with the proper arrangement of collagen fibrils, disrupt nerve fibers, and cause devastating secondary pathophysiological cascades including inflammation, oxidative stress, and other disruptions to intracellular and extracellular homeostasis. A greater understanding of the natural history of MPS I will allow early diagnosis and timely management of the disease facilitating better treatment outcomes.

A case study of three patients with mucopolysaccharidoses in Hue Central Hospital

Mucopolysaccharidosis is a group of rare metabolic disorders characterized by a deficiency of enzymes in the degradation of glycosaminoglycans. The incomplete degradation process leads to the accumulation of glycosaminoglycans in lysosomes of various tissues, which interferes with cell function. We report three cases that were classified as Hurler-Mucopolysaccharidosis I, Morquio-Mucopolysaccharidosis IV A, and Maroteaux-Lamy-Mucopolysaccharidosis VI. Clinical presentations of these cases vary, depending on each type of enzyme defect. All the patients appeared healthy at birth, and symptoms appear at around 1 or 2 years. Clinical features, radiological findings, and especially enzyme assays have allowed us to establish a definitive diagnosis in these cases. These cases highlight that abnormal clinical symptoms, such as growth failure, coarse facial features, and joint problems, are key points for further investigation relating to mucopolysaccharidosis disease. However, in low- and middle-income countries, it is difficult to have a definitive diagnosis of one of the mucopolysaccharidoses due to lacking enzyme assays.

The long-term safety and efficacy of vestronidase alfa, rhGUS enzyme replacement therapy, in subjects with mucopolysaccharidosis VII

Vestronidase alfa (recombinant human beta-glucuronidase) is an enzyme replacement therapy (ERT) for Mucopolysaccharidosis (MPS) VII, a highly heterogeneous, ultra-rare disease. Twelve subjects, ages 8-25 years, completed a Phase 3, randomized, placebo-controlled, blind-start, single crossover study (UX003-CL301; NCT02377921), receiving 24-48 weeks of vestronidase alfa 4 mg/kg IV. All 12 subjects completed the blind-start study, which showed significantly reduced urinary glycosaminoglycans (GAG) and clinical improvement in a multi-domain responder index, and enrolled in a long-term, open-label, extension study (UX003-CL202; NCT02432144). Here, we report the final results of the extension study, up to an additional 144 weeks after completion of the blind-start study. Three subjects (25%) completed all 144 weeks of study, eight subjects (67%) ended study participation before Week 144 to switch to commercially available vestronidase alfa, and one subject discontinued due to non-compliance after receiving one infusion of vestronidase alfa in the extension study. The safety profile of vestronidase alfa in the extension study was consistent with observations in the preceding blind-start study, with most adverse events mild to moderate in severity. There were no treatment or study discontinuations due to AEs and no noteworthy changes in a standard safety chemistry panel. Out of the eleven subjects who tested positive for anti-drug antibodies at any time during the blind-start or extension study, including the baseline assessment in the blind-start study, seven subjects tested positive for neutralizing antibodies and all seven continued to demonstrate a reduction in urinary GAG levels. There was no association between antibody formation and infusion associated reactions. Subjects receiving continuous vestronidase alfa treatment showed a sustained urinary GAG reduction and clinical response evaluated using a multi-domain responder index that includes assessments in pulmonary function, motor function, range of motion, mobility, and visual acuity. Reduction in fatigue was also maintained in the overall population. As ERT is not expected to cross the blood brain barrier, limiting the impact on neurological signs of disease, and not all subjects presented with neurological symptoms, outcomes related to central nervous system pathology are not focused on in this report. Results from this study show the long-term safety and durability of clinical efficacy in subjects with MPS VII with long-term vestronidase alfa treatment.

Projected Retained Ability Score (PRAS): A New Methodology for Quantifying Absolute Change in Norm-Based Psychological Test Scores Over Time

A limitation of norm-based ability test scores is that they can only be used to evaluate relative change (compared with change in the norm sample), as opposed to absolute (raw) change in performance from Time 1 to Time 2. To address this limitation, a novel method (Projected Retained Ability Score [PRAS]) was developed to characterize absolute change in norm-based ability test scores. The PRAS method was applied to Differential Ability Scales®–Second Edition (DAS-II) General Conceptual Ability (GCA) scores in three cases of children with the neurodegenerative condition mucopolysaccharidosis type II (MPS II) who were assessed at two visits, 16 to 23 months apart. Although all three cases showed declines in norm-based GCA scores, the PRAS method revealed differences in absolute change in performance. The PRAS method allows for differentiation of slower-than-average improvement or stabilization versus deterioration of cognitive ability when norm-based scores decline from Time 1 to Time 2.

Neurobehavioral phenotypes of neuronopathic mucopolysaccharidoses

Mucopolysaccharidoses (MPS) are a group of lysosomal multisystemic, chronic, and progressive diseases characterized by the storage of glycosaminoglycans (GAGs) that may affect the central nervous system. Neuronopathic MPS such as MPS IH, MPS II, MPS IIIA–D, and MPS VII are characterized by neurocognitive regression. In severe MPS I (MPS IH, or Hurler syndrome) initial developmental trajectory is usually unremarkable but cognitive development shows a plateau by 2 to 4 years of age and then progressively regresses with aging. Patients with neuronopathic MPS II have a plateau of cognitive and adaptive development on average by 4 to 4.5 years of age, although there is significant variability, followed by progressive neurocognitive decline. In patients with classic MPS III, developmental trajectory reaches a plateau around 3 years of age, followed by regression. Sleep disturbances and behavioral problems occur early in MPS II and III with features of externalizing disorders. Acquired autism-like behavior is often observed in children with MPS III after 4–6 years of age. Impaired social and communication abilities do occur, but MPS III children do not have restricted and repetitive interests such as in autism spectrum disorder. MPS type VII is an ultra-rare neuronopathic MPS with a wide clinical spectrum from very severe with early mortality to milder phenotypes with longer survival into adolescence and adulthood. Most patients with MPS VII have intellectual disability and severely delayed speech development, usually associated with hearing impairment. Cognitive regression in neuronopathic MPS runs parallel to a significant decrease in brain tissue volume. Assessment of the developmental profile is challenging because of low cognitive abilities, physical impairment, and behavioral disturbances. Early diagnosis is crucial as different promising treatment approaches have been extensively studied in animal MPS models and are currently being applied in clinical trials.

Clinical presentation and diagnosis of mucopolysaccharidoses

Mucopolysaccharidoses (MPS) are estimated to affect1 in 25,000 live births although specific rates vary between the ethnic origin and country. MPS are a group of lysosomal storage disorders, which cause the buildup of GAG(s) due to insufficient or absent GAG-degrading enzymes. With seven types of MPS disorders and eleven subtypes, the MPS family presents unique challenges for early clinical diagnosis due to the molecular and clinical heterogeneity between groups and patients. Novel methods of early identification, particularly newborn screening through mass spectrometry, can change the flow of diagnosis, allowing enzyme and GAG quantification before the presentation of clinical symptoms improving outcomes. Genetic testing of patients and their families can also be conducted preemptively. This testing enables families to make informed decisions about family planning, leading to prenatal diagnosis. In this review, we discuss the clinical symptoms of each MPS type as they initially appear in patients, biochemical and molecular diagnostic methods, and the future of newborn screening for this group of disorders.

Beneath the floor: re-analysis of neurodevelopmental outcomes in untreated Hurler syndrome

Background

Hurler syndrome (MPS IH), the severe, neurodegenerative form of type one mucopolysaccharidosis, is associated with rapid neurocognitive decline during toddlerhood and multi-system dysfunction. It is now standardly treated with hematopoietic cell transplantation (HCT), which halts accumulating disease pathology and prevents early death. While norm-based data on developmental functioning in untreated children have previously demonstrated neurocognitive decline, advances in methodology for understanding the cognitive functioning of children with neurodegenerative diseases have highlighted that the previous choice of scores to report results was not ideal. Specifically, the lowest possible norm-based score is 50, which obscures the complete range of cognitive functioning at more advanced stages of neurodeterioration. To a set of cognitive data collected on a sample of untreated children, we applied a modern method of score analysis, calculating a developmental quotient based on age equivalent scores, to reveal the full range of cognitive functioning beneath this cutoff of 50, uncovering new information about the rapidity of decline and the profound impairment in these children.

Results

Among 39 observations for 32 patients with untreated Hurler syndrome, the full array of cognitive functioning below 50 includes many children in the severely to profoundly impaired range. The loss of skills per time unit was 14 points between age 1 and 2. There was a very large range of developmental quotients corresponding to the norm-based cutoff of 50.

Conclusions

This report enables clarification of functioning at levels that extend beneath the floor of 50 in previous work. At the dawn of newborn screening and amidst a proliferation of new therapies for MPS I, these data can provide crucial benchmark information for developing treatments, particularly for areas of the world where transplant may not be available.

Cognitive endpoints for therapy development for neuronopathic mucopolysaccharidoses: Results of a consensus procedure

The design and conduct of clinical studies to evaluate the effects of novel therapies on central nervous system manifestations in children with neuronopathic mucopolysaccharidoses is challenging. Owing to the rarity of these disorders, multinational studies are often needed to recruit enough patients to provide meaningful data and statistical power. This can make the consistent collection of reliable data across study sites difficult. To address these challenges, an International MPS Consensus Conference for Cognitive Endpoints was convened to discuss approaches for evaluating cognitive and adaptive function in patients with mucopolysaccharidoses. The goal was to develop a consensus on best practice for the design and conduct of clinical studies investigating novel therapies for these conditions, with particular focus on the most appropriate outcome measures for cognitive function and adaptive behavior. The outcomes from the consensus panel discussion are reported here.