Neurocognition across the spectrum of mucopolysaccharidosis type I: Age, severity, and treatment

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.

[Inborn error of metabolism and allogenic hematopoietic cell transplantation: Guidelines from the SFGM-TC]

Inherited Metabolic Diseases (IMD) are rare genetic diseases, including both lysosomal and peroxisomal diseases. Lysosomal diseases are related to the deficiency of one or more lysosomal enzymes or transporter. Lysosomal diseases are progressive and involve several tissues with most often neurological damage. Among peroxisomal diseases, X-linked adrenoleukodystrophy (ALD) is a neurodegenerative disease combining neurological and adrenal damage. For these diseases, enzyme replacement therapy (ERT), allogeneic hematopoietic cell transplantation (allo-HCT) and gene therapy represent various possible treatment options, used alone or in combination. The purpose of this workshop is to describe the indications, modalities, and follow-up of allo-HCT as well as the use of ERT peri-transplant. All indications for transplant in these rare diseases are associated with comorbidities and are subject to criteria that must be discussed in a dedicated national multidisciplinary consultation meeting. There are some consensual indications in type I-H mucopolysaccharidosis (MPS-IH) and in the cerebral form of ALD. For other IMDs, no clear benefit from the transplant has been demonstrated. The ideal donor is a non-heterozygous HLA-identical sibling. The recommended conditioning is myeloablative combining fludarabine and busulfan. In MPS-IH, ERT has to be started at diagnosis and continued until complete chimerism and normal enzyme assay are achieved. The pre-transplant assessment and post-transplant follow-up are made according to the published recommendations (PNDS). Standard follow-up is carried out jointly by the transplant and referral teams.

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.

Mucopolysaccharidosis Type 1 among Children-Neuroradiological Perspective Based on Single Centre Experience and Literature Review

Mucopolysaccharidosis 1 (MPS 1) is a group of rare lysosomal genetic disorders resulting from the accumulation of undegraded glycosaminoglycans (GAGs) leading to multiorgan damage. Neurological symptoms vary from mild to severe. Neuroimaging-mainly magnetic resonance (MRI)-plays a crucial role in disease diagnosis and monitoring. Early diagnosis is of the utmost importance due to the necessity of an early therapy implementation. New imaging tools like MR spectroscopy (MRS), semiquantitative MRI analysis and applying scoring systems help substantially in MPS 1 surveillance. The presented analysis of neuroimaging manifestations is based on 5 children with MPS 1 and a literature review. The vigilance of the radiologist based on knowledge of neuroradiological patterns is highlighted.

Pathogenic Roles of Heparan Sulfate and Its Use as a Biomarker in Mucopolysaccharidoses

Heparan sulfate (HS) is an essential glycosaminoglycan (GAG) as a component of proteoglycans, which are present on the cell surface and in the extracellular matrix. HS-containing proteoglycans not only function as structural constituents of the basal lamina but also play versatile roles in various physiological processes, including cell signaling and organ development. Thus, inherited mutations of genes associated with the biosynthesis or degradation of HS can cause various diseases, particularly those involving the bones and central nervous system (CNS). Mucopolysaccharidoses (MPSs) are a group of lysosomal storage disorders involving GAG accumulation throughout the body caused by a deficiency of GAG-degrading enzymes. GAGs are stored differently in different types of MPSs. Particularly, HS deposition is observed in patients with MPS types I, II, III, and VII, all which involve progressive neuropathy with multiple CNS system symptoms. While therapies are available for certain symptoms in some types of MPSs, significant unmet medical needs remain, such as neurocognitive impairment. This review presents recent knowledge on the pathophysiological roles of HS focusing on the pathogenesis of MPSs. We also discuss the possible use and significance of HS as a biomarker for disease severity and therapeutic response in MPSs.

Mucopolysaccharidoses and the blood-brain barrier

Mucopolysaccharidoses comprise a set of genetic diseases marked by an enzymatic dysfunction in the degradation of glycosaminoglycans in lysosomes. There are eight clinically distinct types of mucopolysaccharidosis, some with various subtypes, based on which lysosomal enzyme is deficient and symptom severity. Patients with mucopolysaccharidosis can present with a variety of symptoms, including cognitive dysfunction, hepatosplenomegaly, skeletal abnormalities, and cardiopulmonary issues. Additionally, the onset and severity of symptoms can vary depending on the specific disorder, with symptoms typically arising during early childhood. While there is currently no cure for mucopolysaccharidosis, there are clinically approved therapies for the management of clinical symptoms, such as enzyme replacement therapy. Enzyme replacement therapy is typically administered intravenously, which allows for the systemic delivery of the deficient enzymes to peripheral organ sites. However, crossing the blood-brain barrier (BBB) to ameliorate the neurological symptoms of mucopolysaccharidosis continues to remain a challenge for these large macromolecules. In this review, we discuss the transport mechanisms for the delivery of lysosomal enzymes across the BBB. Additionally, we discuss the several therapeutic approaches, both preclinical and clinical, for the treatment of mucopolysaccharidoses.

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.

Quantitative brain MRI morphology in severe and attenuated forms of mucopolysaccharidosis type I

OBJECTIVE

To assess our hypothesis that brain macrostructure is different in individuals with mucopolysaccharidosis type I (MPS I) and healthy controls (HC), we conducted a comprehensive multicenter study using a uniform quantitative magnetic resonance imaging (qMRI) protocol, with analyses that account for the effects of disease phenotype, age, and cognition.

METHODS

Brain MRIs in 23 individuals with attenuated (MPS IA) and 38 with severe MPS I (MPS IH), aged 4-25 years, enrolled under the study protocol NCT01870375, were compared to 98 healthy controls.

RESULTS

Cortical and subcortical gray matter, white matter, corpus callosum, ventricular and choroid plexus volumes in MPS I significantly differed from HC. Thicker cortex, lower white matter and corpus callosum volumes were already present at the youngest MPS I participants aged 4-5 years. Age-related differences were observed in both MPS I groups, but most markedly in MPS IH, particularly in cortical gray matter metrics. IQ scores were inversely associated with ventricular volume in both MPS I groups and were positively associated with cortical thickness only in MPS IA.

CONCLUSIONS

Quantitatively-derived MRI measures distinguished MPS I participants from HC as well as severe from attenuated forms. Age-related neurodevelopmental trajectories in both MPS I forms differed from HC. The extent to which brain structure is altered by disease, potentially spared by treatment, and how it relates to neurocognitive dysfunction needs further exploration.

Evidence of Treatment Benefits in Patients with Mucopolysaccharidosis Type I-Hurler in Long-term Follow-up Using a New Magnetic Resonance Imaging Scoring System

We developed a brain and spine magnetic resonance scoring system based on a magnetic resonance assessment of 9 patients with mucopolysaccharidosis type I-Hurler who underwent hematopoietic stem-cell transplantation. The score is reliable and correlates with long-term clinical and cognitive outcome in patients with mucopolysaccharidosis type I-Hurler.

Chitotriosidase as a biomarker for gangliosidoses

Elevated serum chitotriosidase (CHITO) is an indication of macrophage activation, and its capacity have been explored as a marker of inflammation in a number of disease states. For over a decade, CHITO plasma levels have been used by clinicians as a biomarker of inflammation in the lysosomal disease, Gaucher disease, including monitoring response to therapies in patients with Gaucher disease type I. Although it is becoming increasingly recognized that inflammation is a prominent component of many lysosomal diseases, the relation of CHITO levels to disease burden has not been well-characterized in the large majority of lysosomal diseases. Moreover, the role of CHITO in lysosomal diseases that affect the central nervous system (CNS) has not been systematically studied. In this study, one hundred and thirty-four specimens of CSF and serum were collected from 34 patients with lysosomal diseases affecting the CNS. This study included patients with GM1-gangliosidosis, GM2-gangliosidosis, mucopolysaccharidoses (MPS), multiple sulfatase deficiency and Gaucher disease. CHITO levels in the CSF were significantly higher in patients with more rapidly progressing severe neurological impairment: GM1-gangliosidosis vs MPS (p < 0.0001); GM2-gangliosidosis vs MPS (p < 0.0001). CHITO levels were higher in patients with the more severe phenotypes compared to milder phenotypes in GM1-gangliosidosis and GM2-gangliosidosis (serum CHITO in GM1-gangliosidosis infantile vs juvenile p = 0.025; CSF CHITO in Tay-Sachs infantile vs Tay-Sachs late-onset p < 0.0001). Moreover, higher CHITO levels in the CSF were significantly associated with lower cognitive test scores in patients with GM1-gangliosidosis, GM2-gangliosidosis, and MPS (p = 1.12*10^-5, R² = 0.72). Patients with infantile GM1-gangliosidosis showed increasing CSF CHITO over time, suggesting that CSF CHITO reflects disease progression and a possible surrogate endpoint for future clinical trials with infantile GM1-gangliosidosis. In summary, these results support the use of CSF CHITO to diagnose between different disease phenotypes and as a valuable tool for monitoring disease progression in patients. These results necessitate the inclusion of CHITO as an exploratory biomarker for clinical trials.

Issues of COVID-19-related distance learning for children with neuronopathic mucopolysaccharidoses

The COVID-19 pandemic has impacted the education of children around the world, forcing a large proportion of teaching to be carried out remotely. The implications of this disruption have yet to be fully elucidated, but initial assessments suggest that COVID-19-related school closures and reliance on virtual learning may have a long-term negative impact on educational attainment and future earnings as well as life expectancy of children in the United States. Among children with neurodegenerative disorders, such as neuronopathic mucopolysaccharidoses (MPS disorders), the effects of the pandemic are likely to be even greater. We aim to shine a spotlight on the impact of COVID-19 on the education, treatment and general wellbeing of children and families affected by MPS disorders by highlighting the important role that educators and therapists play in supporting the neurocognitive function and quality of life of children with neuronopathic MPS disorders. This article will serve as a resource that caregivers, educators, clinicians and therapists can use when considering how best to advocate for children with neuronopathic MPS disorders in circumstances where in-school teaching or in-clinic treatment is compromised or not possible. Given that the current pandemic is likely to have a prolonged course and impact and that similar epidemics and pandemics are a near certainty in the future, it is essential that steps are taken to support the learning and care of children with neuronopathic MPS disorders. We must prioritize strategies to safely resume this fragile community's access to in-person education and supportive care, and to address gaps that have emerged during prolonged pauses in access, whenever possible.

Differences in MPS I and MPS II Disease Manifestations

Mucopolysaccharidosis (MPS) type I and II are two closely related lysosomal storage diseases associated with disrupted glycosaminoglycan catabolism. In MPS II, the first step of degradation of heparan sulfate (HS) and dermatan sulfate (DS) is blocked by a deficiency in the lysosomal enzyme iduronate 2-sulfatase (IDS), while, in MPS I, blockage of the second step is caused by a deficiency in iduronidase (IDUA). The subsequent accumulation of HS and DS causes lysosomal hypertrophy and an increase in the number of lysosomes in cells, and impacts cellular functions, like cell adhesion, endocytosis, intracellular trafficking of different molecules, intracellular ionic balance, and inflammation. Characteristic phenotypical manifestations of both MPS I and II include skeletal disease, reflected in short stature, inguinal and umbilical hernias, hydrocephalus, hearing loss, coarse facial features, protruded abdomen with hepatosplenomegaly, and neurological involvement with varying functional concerns. However, a few manifestations are disease-specific, including corneal clouding in MPS I, epidermal manifestations in MPS II, and differences in the severity and nature of behavioral concerns. These phenotypic differences appear to be related to different ratios between DS and HS, and their sulfation levels. MPS I is characterized by higher DS/HS levels and lower sulfation levels, while HS levels dominate over DS levels in MPS II and sulfation levels are higher. The high presence of DS in the cornea and its involvement in the arrangement of collagen fibrils potentially causes corneal clouding to be prevalent in MPS I, but not in MPS II. The differences in neurological involvement may be due to the increased HS levels in MPS II, because of the involvement of HS in neuronal development. Current treatment options for patients with MPS II are often restricted to enzyme replacement therapy (ERT). While ERT has beneficial effects on respiratory and cardiopulmonary function and extends the lifespan of the patients, it does not significantly affect CNS manifestations, probably because the enzyme cannot pass the blood-brain barrier at sufficient levels. Many experimental therapies, therefore, aim at delivery of IDS to the CNS in an attempt to prevent neurocognitive decline in the patients.

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.

Long term disease burden post-transplantation: three decades of observations in 25 Hurler patients successfully treated with hematopoietic stem cell transplantation (HSCT)

BACKGROUND

Mucopolysaccharidosis type I-Hurler syndrome (MPSI-H) is a lysosomal storage disease characterized by severe physical symptoms and cognitive decline. Early treatment with hematopoietic cell transplant (HSCT) is critical to the survival of these patients. While survival rates and short-term outcomes are known to be improved by HSCT, the long-term cognitive, adaptive and psychosocial functional outcomes of children with (MPSI-H) post-HSCT are not well documented. This manuscript focuses on retrospective long-term follow-up (7-33 years) of 25 MPSI-H patients, transplanted between 1986 and 2011.

RESULTS

The median age at transplantation was 21 months (range 12-57 months). Except for one death, all successfully transplanted MPSI-H patients surviving at least 1 year after HSCT are alive to-date, with a median age of 21 years (range 8-36 years) at the last follow-up evaluation. A majority of HSCT grafts were bone marrow transplants (BMT), resulting in durable full chimerism in 18 (72%). Pre-HSCT, the onset of first symptoms occurred very early, at a median age of 3 months (range birth-16 months). The most prevalent symptoms before MPSI-H diagnosis involved progressive dysostosis multiplex; almost all patients suffered from hip dysplasia and thoracolumbar spine Kyphosis. Despite HSCT, considerable residual disease burden and ensuing corrective surgical interventions were observed in all, and at every decade of follow-up post HSCT. Late-onset psychiatric manifestations were significant (n = 17 patients; 68%), including depression in 13 patients at a median onset age of 18 years (range 13-31 years), hyperactivity and attention deficit disorder (n = 4), and multiple acute psychotic episodes (APE), independent of depression observed (n = 3) at a median onset age of 18 years (range 17-31 years). The adult Welscher Intelligence Scale results (n = 16) were heterogenous across the four scale dimensions; overall lower scores were observed on both working memory index (median WMI = 69.5) and processing speed index (median PSI = 65), whereas verbal comprehension index (median VCI = 79) and perceptual reasoning index (median PRI = 74) were higher.

CONCLUSION

With advanced treatment options, MPSI-H are living into 3rd and 4th decades of life, however not disease free and with poor adaptation. Residual disease (loss of mobility, limited gross and fine motor skills; low cognitive ability; suboptimal cardiopulmonary function, vision and hearing) negatively impacts the quality of life and psychosocial functioning of affected individuals.

Mucopolysaccharidosis Type I: Current Treatments, Limitations, and Prospects for Improvement

Mucopolysaccharidosis type I (MPS I) is a lysosomal disease, caused by a deficiency of the enzyme alpha-L-iduronidase (IDUA). IDUA catalyzes the degradation of the glycosaminoglycans dermatan and heparan sulfate (DS and HS, respectively). Lack of the enzyme leads to pathologic accumulation of undegraded HS and DS with subsequent disease manifestations in multiple organs. The disease can be divided into severe (Hurler syndrome) and attenuated (Hurler-Scheie, Scheie) forms. Currently approved treatments consist of enzyme replacement therapy (ERT) and/or hematopoietic stem cell transplantation (HSCT). Patients with attenuated disease are often treated with ERT alone, while the recommended therapy for patients with Hurler syndrome consists of HSCT. While these treatments significantly improve disease manifestations and prolong life, a considerable burden of disease remains. Notably, treatment can partially prevent, but not significantly improve, clinical manifestations, necessitating early diagnosis of disease and commencement of treatment. This review discusses these standard therapies and their impact on common disease manifestations in patients with MPS I. Where relevant, results of animal models of MPS I will be included. Finally, we highlight alternative and emerging treatments for the most common disease manifestations.

Case Report: Cerebral Revascularization in a Child With Mucopolysaccharidosis Type I

Mucopolysaccharidosis (MPS) type I is a rare lysosomal storage disorder caused by an accumulation of glycosaminoglycans (GAGs) resulting in multisystem disease. Neurological morbidity includes hydrocephalus, spinal cord compression, and cognitive decline. While many neurological symptoms have been described, stroke is not a widely-recognized manifestation of MPS I. Accordingly, patients with MPS I are not routinely evaluated for stroke, and there are no guidelines for managing stroke in patients with this disease. We report the case of a child diagnosed with MPS I who presented with overt stroke and repeated neurological symptoms with imaging findings for severe ventriculomegaly, infarction, and bilateral terminal carotid artery stenosis. Direct intracranial pressure evaluation proved negative for hydrocephalus. The patient was subsequently treated with cerebral revascularization and at a 3-year follow-up, the patient reported no further neurological events or new ischemia on cerebral imaging. Cerebral arteriopathy in patients with MPS I may be associated with GAG accumulation within the cerebrovascular system and may predispose patients to recurrent strokes. However, further studies are required to elucidate the etiology of cerebrovascular arteriopathy in the setting of MPS I. Although the natural history of steno-occlusive arteriopathy in patients with MPS I remains unclear, our findings suggest that cerebral revascularization is a safe treatment option that may mitigate the risk of future strokes and should be strongly considered within the overall management guidelines for patients with MPS I.

Induced Pluripotent Stem Cells to Understand Mucopolysaccharidosis. I: Demonstration of a Migration Defect in Neural Precursors

Background: Mucopolysaccharidosis type I-Hurler (MPS1-H) is a severe genetic lysosomal storage disorder due to loss-of-function mutations in the IDUA gene. The subsequent complete deficiency of alpha l-iduronidase enzyme is directly responsible of a progressive accumulation of glycosaminoglycans (GAG) in lysosomes which affects the functions of many tissues. Consequently, MPS1 is characterized by systemic symptoms (multiorgan dysfunction) including respiratory and cardiac dysfunctions, skeletal abnormalities and early fatal neurodegeneration. Methods: To understand mechanisms underlying MPS1 neuropathology, we generated induced pluripotent stem cells (iPSC) from a MPS1-H patient with loss-of-function mutations in both IDUA alleles. To avoid variability due to different genetic background of iPSC, we established an isogenic control iPSC line by rescuing IDUA expression by a lentivectoral approach. Results: Marked differences between MPS1-H and IDUA-corrected isogenic controls were observed upon neural differentiation. A scratch assay revealed a strong migration defect of MPS1-H cells. Also, there was a massive impact of IDUA deficiency on gene expression (340 genes with an FDR <0.05). Conclusions: Our results demonstrate a hitherto unknown connection between lysosomal degradation, gene expression and neural motility, which might account at least in part for the phenotype of MPS1-H patients.

Update on Clinical Ex Vivo Hematopoietic Stem Cell Gene Therapy for Inherited Monogenic Diseases

Gene transfer into autologous hematopoietic stem progenitor cells (HSPCs) has the potential to cure monogenic inherited disorders caused by an altered development and/or function of the blood system, such as immune deficiencies and red blood cell and platelet disorders. Gene-corrected HSPCs and their progeny can also be exploited as cell vehicles to deliver molecules into the circulation and tissues, including the central nervous system. In this review, we focus on the progress of clinical development of medicinal products based on HSPCs engineered and modified by integrating viral vectors for the treatment of monogenic blood disorders and metabolic diseases. Two products have reached the stage of market approval in the EU, and more are foreseen to be approved in the near future. Despite these achievements, several challenges remain for HSPC gene therapy (HSPC-GT) precluding a wider application of this type of gene therapy to a wider set of diseases while gene-editing approaches are entering the clinical arena.

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.

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.

Myelin and Lipid Composition of the Corpus Callosum in Mucopolysaccharidosis Type I Mice

Mucopolysaccharidosis type I (MPS I) is a lysosomal disease with progressive central nervous system involvement. This study examined the lipid, cholesterol, and myelin basic protein composition of white matter in the corpus callosum of MPS I mice. We studied 50 week-old, male MPS I mice and littermate, heterozygote controls (n = 12 per group). Male MPS I mice showed lower phosphatidylcholine and ether-linked phosphatidylcholine quantities than controls (p < 0.05). Twenty-two phospholipid or ceramide species showed significant differences in percent of total. Regarding specific lipid species, MPS I mice exhibited lower quantities of sphingomyelin 18:1, phosphatidylserine 38:3, and hexosylceramide d18:1(22:1) mH₂ O than controls. Principal components analyses of polar, ceramide, and hexosylceramide lipids, respectively, showed some separation of MPS I and control mice. We found no significant differences in myelin gene expression, myelin basic protein, or total cholesterol in the MPS I mice versus heterozygous controls. There was a trend toward lower proteolipid protein-1 levels in MPS I mice (p = 0.06). MPS I mice show subtle changes in white matter composition, with an unknown impact on pathogenesis in this model.

Mucopolysaccharidosis Type I

Mucopolysaccharidosis type I (MPS I) is caused by the deficiency of α-l-iduronidase, leading to the storage of dermatan and heparan sulfate. There is a broad phenotypical spectrum with the presence or absence of neurological impairment. The classical form is known as Hurler syndrome, the intermediate form as Hurler-Scheie, and the most attenuated form is known as Scheie syndrome. Phenotype seems to be largely influenced by genotype. Patients usually develop several somatic symptoms such as abdominal hernias, extensive dermal melanocytosis, thoracolumbar kyphosis odontoid dysplasia, arthropathy, coxa valga and genu valgum, coarse facial features, respiratory and cardiac impairment. The diagnosis is based on the quantification of α-l-iduronidase coupled with glycosaminoglycan analysis and gene sequencing. Guidelines for treatment recommend hematopoietic stem cell transplantation for young Hurler patients (usually at less than 30 months of age). Intravenous enzyme replacement is approved and is the standard of care for attenuated-Hurler-Scheie and Scheie-forms (without cognitive impairment) and for the late-diagnosed severe-Hurler-cases. Intrathecal enzyme replacement therapy is under evaluation, but it seems to be safe and effective. Other therapeutic approaches such as gene therapy, gene editing, stop codon read through, and therapy with small molecules are under development. Newborn screening is now allowing the early identification of MPS I patients, who can then be treated within their first days of life, potentially leading to a dramatic change in the disease's progression. Supportive care is very important to improve quality of life and might include several surgeries throughout the life course.

Cognitive Abilities of Dogs with Mucopolysaccharidosis I: Learning and Memory

Mucopolysaccharidosis I (MPS I) results from a deficiency of a lysosomal enzyme, alpha-L-iduronidase (IDUA). IDUA deficiency leads to glycosaminoglycan (GAG) accumulation resulting in cellular degeneration and multi-organ dysfunction. The primary aims of this pilot study were to determine the feasibility of cognitive testing MPS I affected dogs and to determine their non-social cognitive abilities with and without gene therapy. Fourteen dogs were tested: 5 MPS I untreated, 5 MPS I treated, and 4 clinically normal. The treated group received intrathecal gene therapy as neonates to replace the IDUA gene. Cognitive tests included delayed non-match to position (DNMP), two-object visual discrimination (VD), reversal learning (RL), attention oddity (AO), and two-scent discrimination (SD). Responses were recorded as correct, incorrect, or no response, and analyzed using mixed effect logistic regression analysis. Significant differences were not observed among the three groups for DNMP, VD, RL, or AO. The MPS I untreated dogs were excluded from AO testing due to failing to pass acquisition of the task, potentially representing a learning or executive function deficit. The MPS I affected group (treated and untreated) was significantly more likely to discriminate between scents than the normal group, which may be due to an age effect. The normal group was comprised of the oldest dogs, and a mixed effect logistic model indicated that older dogs were more likely to respond incorrectly on scent discrimination. Overall, this study found that cognition testing of MPS I affected dogs to be feasible. This work provides a framework to refine future cognition studies of dogs affected with diseases, including MPS I, in order to assess therapies in a more comprehensive manner.

Evaluation of non-reducing end pathologic glycosaminoglycan detection method for monitoring therapeutic response to enzyme replacement therapy in human mucopolysaccharidosis I

Therapeutic development and monitoring require demonstration of effects on disease phenotype. However, due to the complexity of measuring clinically-relevant effects in rare multisystem diseases, robust biomarkers are essential. For the mucopolysaccharidoses (MPS), the measurement of glycosaminoglycan levels is relevant as glycosaminoglycan accumulation is the primary event that occurs due to reduced lysosomal enzyme activity. Traditional dye-based assays that measure total glycosaminoglycan levels have a high background, due to a normal, baseline glycosaminoglycan content in unaffected individuals. An assay that selectively detects the disease-specific non-reducing ends of heparan sulfate glycosaminoglycans that remain undegraded due to deficiency of a specific enzyme in the catabolic pathway avoids the normal background, increasing sensitivity and specificity. We evaluated glycosaminoglycan content by dye-based and non-reducing end methods using urine, serum, and cerebrospinal fluid from MPS I human samples before and after treatment with intravenous recombinant human alpha-l-iduronidase. We found that both urine total glycosaminoglycans and serum heparan sulfate derived non-reducing end levels were markedly decreased compared to baseline after 26 weeks and 52 weeks of therapy, with a significantly greater percentage reduction in serum non-reducing end (89.8% at 26 weeks and 81.3% at 52 weeks) compared to urine total glycosaminoglycans (68.3% at 26 weeks and 62.4% at 52 weeks, p < 0.001). Unexpectedly, we also observed a decrease in non-reducing end levels in cerebrospinal fluid in all five subjects for whom samples were collected (mean 41.8% reduction, p = 0.01). The non-reducing ends in cerebrospinal fluid showed a positive correlation with serum non-reducing end levels in the subjects (r² = 0.65, p = 0.005). Results suggest utility of the non-reducing end assay in evaluating a therapeutic response in MPS I.

Intrathecal enzyme replacement for cognitive decline in mucopolysaccharidosis type I, a randomized, open-label, controlled pilot study

Central nervous system manifestations of mucopolysaccharidosis type I (MPS I) such as cognitive impairment, hydrocephalus, and spinal cord compression are inadequately treated by intravenously-administered enzyme replacement therapy with laronidase (recombinant human alpha-L-iduronidase). While hematopoietic stem cell transplantation treats neurological symptoms, this therapy is not generally offered to attenuated MPS I patients. This study is a randomized, open-label, controlled pilot study of intrathecal laronidase in eight attenuated MPS I patients with cognitive impairment. Subjects ranged between 12 years and 50 years old with a median age of 18 years. All subjects had received intravenous laronidase prior to the study over a range of 4 to 10 years, with a mean of 7.75 years. Weekly intravenous laronidase was continued throughout the duration of the study. The randomization period was one year, during which control subjects attended all study visits and assessments, but did not receive any intrathecal laronidase. After the first year, all eight subjects received treatment for one additional year. There was no significant difference in neuropsychological assessment scores between control or treatment groups, either over the one-year randomized period or at 18 or 24 months. However, there was no significant decline in scores in the control group either. Adverse events included pain (injection site, back, groin), headache, neck spasm, and transient blurry vision. There were seven serious adverse events, one judged as possibly related (headache requiring hospitalization). There was no significant effect of intrathecal laronidase on cognitive impairment in older, attenuated MPS I patients over a two-year treatment period. A five-year open-label extension study is underway.

A longitudinal study of neurocognition and behavior in patients with Hurler-Scheie syndrome heterozygous for the L238Q mutation

Previous research has demonstrated the mutation, c.712T>A (p.L238Q) of the gene for α-L- iduronidase (IDUA) in patients with Hurler-Scheie syndrome is relatively severe when paired with a nonsense or deletion or splice-site mutation. This mutation was also found to be associated with psychiatric symptoms. This research presents longitudinal data and protein analysis to further investigate the severity and natural history of these unique patients.

Methods

Six patients heterozygous for L238Q were compared to six patients with Hurler-Scheie without the L238Q mutations. Somatic burden of disease, IQ, memory, attention, adaptive functioning and behavioral measures were given yearly over 2 to 4 years from 2009 to 2014. The impact of L238Q on the IDUA enzyme was examined using 7 bioinformatics tools and a 3D structural analysis.

Results

Similar to the cross sectional study, the L238Q patients had more severe abnormalities in IQ, attention, adaptive functioning, and behavioral functioning than the comparison group. There were no major differences between the two groups in change over time; IQ for both groups was stable with some behavioral areas showing improvement. Over time, both groups declined in visual spatial memory and, attention/visual processing. They also showed increased anxiety. Structural and bioinformatics analysis of the L238Q suggest that this mutation causes a significant reduction in the IDUA enzyme's potential catalytic activity, and this mutation may be more severe than other mutations contributing to the Hurler-Scheie syndrome phenotype, presumably causing the psychiatric disease.

Conclusion

L238Q patients demonstrate severe neurocognitive and neurobehavioral deficits but are relatively stable. Like the comparison group, decreasing visual spatial memory and attention and increasing anxiety suggest more intervention in life skills and emotional social supports are needed.

Biochemical and clinical response after umbilical cord blood transplant in a boy with early childhood-onset beta-mannosidosis

BACKGROUND

Deficiency in the enzyme β-mannosidase was described over three decades ago. Although rare in occurrence, the presentation of childhood-onset β-mannosidase deficiency consists of hypotonia in the newborn period followed by global development delay, behavior problems, and intellectual disability. No effective pharmacologic treatments have been available.

METHODS

We report 2-year outcomes following the first umbilical cord blood transplant in a 4-year-old boy with early childhood-onset disease.

RESULTS

We show restoration of leukocyte β-mannosidase activity which remained normal at 2 years posttransplant, and a simultaneous increase in plasma β-mannosidase activity and dramatic decrease in urine-free oligosaccharides were also observed. MRI of the brain remained stable. Neurocognitive evaluation revealed test point gains, although the magnitude of improvement was less than expected for age, causing lower IQ scores that represent a wider developmental gap between the patient and unaffected peers.

CONCLUSION

Our findings suggest that hematopoietic cell transplant can correct the biochemical defect in β-mannosidosis, although preservation of the neurocognitive trajectory may be a challenge.

Intrathecal enzyme replacement for Hurler syndrome: biomarker association with neurocognitive outcomes

PURPOSE

Abnormalities in cerebrospinal fluid (CSF) have been reported in Hurler syndrome, a fatal neurodegenerative lysosomal disorder. While no biomarker has predicted neurocognitive response to treatment, one of these abnormalities, glycosaminoglycan nonreducing ends (NREs), holds promise to monitor therapeutic efficacy. A trial of intrathecal enzyme replacement therapy (ERT) added to standard treatment enabled tracking of CSF abnormalities, including NREs. We evaluated safety, biomarker response, and neurocognitive correlates of change.

METHODS

In addition to intravenous ERT and hematopoietic cell transplantation, patients (N = 24) received intrathecal ERT at four peritransplant time points; CSF was evaluated at each point. Neurocognitive functioning was quantified at baseline, 1 year, and 2 years posttransplant. Changes in CSF biomarkers and neurocognitive function were evaluated for an association.

RESULTS

Over treatment, there were significant decreases in CSF opening pressure, biomarkers of disease activity, and markers of inflammation. Percent decrease in NRE from pretreatment to final intrathecal dose posttransplant was positively associated with percent change in neurocognitive score from pretreatment to 2 years posttransplant.

CONCLUSION

Intrathecal ERT was safe and, in combination with standard treatment, was associated with reductions in CSF abnormalities. Critically, we report evidence of a link between a biomarker treatment response and neurocognitive outcome in Hurler syndrome.

Attention and corpus callosum volumes in individuals with mucopolysaccharidosis type I

OBJECTIVE

Previous research suggests attention and white matter (WM) abnormalities in individuals with mucopolysaccharidosis type I (MPS I); this cross-sectional comparison is one of the first to examine the relationship of WM structural abnormalities as measured by corpus callosum (CC) volumes with attention scores to evaluate this relationship in a larger sample of patients with MPS I.

METHODS

Volumetric MRI data and performance on a computerized measure of sustained attention were compared for 18 participants with the severe form of MPS I (MPS IH), 18 participants with the attenuated form of MPS I (MPS I_ATT), and 60 typically developing age-matched controls.

RESULTS

The MPS I groups showed below-average mean attention scores (p < 0.001) and smaller CC volumes (p < 0.001) than controls. No significant associations were found between attention performance and CC volume for controls. Attention was associated with posterior CC volumes in the participants with MPS IH (p = 0.053) and total (p = 0.007) and anterior (p < 0.001) CC volumes in participants with MPS I_ATT.

CONCLUSIONS

We found that attention and CC volumes were reduced in participants with MPS I compared to typically developing controls. Smaller CC volumes in participants with MPS I were associated with decreased attention; such an association was not seen in controls. While hematopoietic cell transplantation used to treat MPS IH may compound these effects, attention difficulties were also seen in the MPS I_ATT group, suggesting that disease effects contribute substantially to the clinical attentional difficulties seen in this population.

An online survey on burden of illness among families with post-stem cell transplant mucopolysaccharidosis type I children in the United States

Background

Severe mucopolysaccharidosis type I (also known as Hurler syndrome) is a rare devasting recessive genetic disease caused by the deficiency of an enzyme. Hematopoietic stem cell transplant is the standard of care in the United States, usually conducted before the child is 3 years of age, but little is known about the continued medical and educational needs of the child after transplant. A greater understanding of the burden of illness on the primary caregiver is also needed. Therefore, this online survey sought to gather information on the burden of severe MPS I in the United States at least 1 year after transplant.

Results

Thirty-two respondents reported that children with severe MPS I have significant medical and educational needs after transplant. Healthcare resource use was frequent, especially in the outpatient setting specifically for bone, cardiac, and vision complications that were not relieved by HSCT. Twenty-five percent of the children had been hospitalized at least once in the last year and two had been hospitalized twice. The most common reasons for overnight hospitalizations included orthopedic surgeries and respiratory infections. Among children ages 5 and older, only 3 of 28 (11%) were able to attend school with no special support. While caregivers were generally satisfied with the healthcare services their child receives, 69% of working caregivers reported negative impact on their ability to conduct work tasks, and 54% of caregivers did not work so that they could care for the child.

Conclusions

Results suggest that severe MPS I children continue to  require medical care and special support for education. Future research on the burden of illness on families affected by severe MPS I is needed to better understand total cost of care, and to identify therapies and interventions that reduce burden of illness. Future studies that compare cost of and access to health care in different countries may provide a more global view of the burden of MPS I.

Lysosomal storage disease overview

The lysosomal storage diseases (LSDs) are a group of inherited metabolic disorders that are caused for the most part by enzyme deficiencies within the lysosome resulting in accumulation of undegraded substrate. This storage process leads to a broad spectrum of clinical manifestations depending on the specific substrate and site of accumulation. Examples of LSDs include the mucopolysaccharidoses, mucolipidoses, oligosaccharidoses, Pompe disease, Gaucher disease, Fabry disease, the Niemann-Pick disorders, and neuronal ceroid lipofuscinoses. This review summarizes the main clinical features, diagnosis, and management of LSDs with an emphasis on those for which treatment is available.

Late Mortality after Allogeneic Blood or Marrow Transplantation for Inborn Errors of Metabolism: A Report from the Blood or Marrow Transplant Survivor Study-2 (BMTSS-2)

Allogeneic blood or marrow transplantation (BMT) is currently considered the standard of care for patients with specific inborn errors of metabolism (IEM). However, there is a paucity of studies describing long-term survival and cause-specific late mortality after BMT in these patients with individual types of IEM. We studied 273 patients who had survived ≥2 years after allogeneic BMT for IEM performed between 1974 and 2014. The most prevalent IEM in our cohort were X-linked adrenoleukodystrophy (ALD; 37.3%), Hurler syndrome (35.1%), and metachromatic leukodystrophy (MLD; 10.2%). Conditional on surviving ≥2 years after BMT, the overall survival for the entire cohort was 85.5 ± 2.4% at 10 years and 73.5 ± 3.7% at 20 years. The cohort had a 29-fold increased risk of late death compared with an age- and sex-matched cohort from the general US population (95% CI, 22- to 38-fold). The increased relative mortality was highest in the 2- to 5-year period after BMT (standardized mortality ratio [SMR], 207; 95% confidence interval [CI], 130 to 308) and declined with increasing time from BMT, but remained elevated for ≥21 years after BMT (SMR, 9; 95% CI, 4 to 18). Sequelae from the progression of primary disease were the most common causes of late mortality in this cohort (76%). The use of T cell-depleted grafts in patients with ALD and Hurler syndrome was a risk factor for late mortality. Younger age at BMT and use of busulfan and cyclosporine were protective in patients with Hurler syndrome. Our findings demonstrate relatively favorable overall survival in ≥2-year survivors of allogeneic BMT for IEM, although primary disease progression continues to be responsible for the majority of late deaths.

Treatment of thoracolumbar kyphosis in patients with mucopolysaccharidosis type I: results of an international consensus procedure

Background

In all patients with mucopolysaccharidosis type I (MPS I), skeletal disease (dysostosis multiplex) is a prominent, debilitating, condition related complication that may impact strongly on activities of daily living. Unfortunately, it is not alleviated by treatment with hematopoietic cell transplantation (HCT) or enzyme replacement therapy (ERT). Although early kyphosis is one of the key features of dysostosis multiplex, there is no international consensus on the optimal management. Therefore, an international consensus procedure was organized with the aim to develop the first clinical practice guideline for the management of thoracolumbar kyphosis in MPS I patients.

Methods

A literature review was conducted to identify all available information about kyphosis and related surgery in MPS I patients. Subsequently, a modified Delphi procedure was used to develop consensus statements. The expert panel included 10 spinal orthopedic surgeons, 6 pediatricians and 3 physiotherapists, all experienced in MPS I. The procedure consisted of 2 written rounds, a face-to-face meeting and a final written round. The first 2 rounds contained case histories, general questions and draft statements. During the face-to-face meeting consensus statements were developed. In the final round, the panel had the opportunity to anonymously express their opinion about the proposed statements.

Results

Eighteen case series and case reports were retrieved from literature reporting on different surgical approaches and timing of thoracolumbar kyphosis surgery in MPS I. During the face-to-face meeting 16 statements were discussed and revised. Consensus was reached on all statements.

Conclusion

This international consensus procedure resulted in the first clinical practice guideline for the management of thoracolumbar kyphosis in MPS I patients, focusing on the goals and timing of surgery, as well as the optimal surgical approach, the utility of bracing and required additional assessments (e.g. radiographs). Most importantly, it was concluded that the decision for surgery depends not only on the kyphotic angle, but also on additional factors such as the progression of the deformity and its flexibility, the presence of symptoms, growth potential and comorbidities. The eventual goal of treatment is the maintenance or improvement of quality of life. Further international collaborative research related to long-term outcome of kyphosis surgery in MPS I is essential as prognostic information is lacking.

Electronic supplementary material

The online version of this article (10.1186/s13023-019-0997-5) contains supplementary material, which is available to authorized users.

Lysosomal storage disease overview

The lysosomal storage diseases (LSDs) are a group of inherited metabolic disorders that are caused for the most part by enzyme deficiencies within the lysosome resulting in accumulation of undegraded substrate. This storage process leads to a broad spectrum of clinical manifestations depending on the specific substrate and site of accumulation. Examples of LSDs include the mucopolysaccharidoses, mucolipidoses, oligosaccharidoses, Pompe disease, Gaucher disease, Fabry disease, the Niemann-Pick disorders, and neuronal ceroid lipofuscinoses. This review summarizes the main clinical features, diagnosis, and management of LSDs with an emphasis on those for which treatment is available.

Anatomical changes and pathophysiology of the brain in mucopolysaccharidosis disorders

Mucopolysaccharidosis (MPS) disorders are caused by deficiencies in lysosomal enzymes, leading to impaired glycosaminoglycan (GAG) degradation. The resulting GAG accumulation in cells and connective tissues ultimately results in widespread tissue and organ dysfunction. The seven MPS types currently described are heterogeneous and progressive disorders, with somatic and neurological manifestations depending on the type of accumulating GAG. Heparan sulfate (HS) is one of the GAGs stored in patients with MPS I, II, and VII and the main GAG stored in patients with MPS III. These disorders are associated with significant central nervous system (CNS) abnormalities that can manifest as impaired cognition, hyperactive and/or aggressive behavior, epilepsy, hydrocephalus, and sleeping problems. This review discusses the anatomical and pathophysiological CNS changes accompanying HS accumulation as well as the mechanisms believed to cause CNS abnormalities in MPS patients. The content of this review is based on presentations and discussions on these topics during a meeting on the brain in MPS attended by an international group of MPS experts.

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.

Long-term outcomes of systemic therapies for Hurler syndrome: an international multicenter comparison

PURPOSE

Early treatment is critical for mucopolysaccharidosis type I (MPS I), justifying its incorporation into newborn screening. Enzyme replacement therapy (ERT) treats MPS I, yet presumptions that ERT cannot penetrate the blood-brain barrier (BBB) support recommendations that hematopoietic cell transplantation (HCT) treat the severe, neurodegenerative form (Hurler syndrome). Ethics precludes randomized comparison of ERT with HCT, but insight into this comparison is presented with an international cohort of patients with Hurler syndrome who received long-term ERT from a young age.

METHODS

Long-term survival and neurologic outcomes were compared among three groups of patients with Hurler syndrome: 18 treated with ERT monotherapy (ERT group), 54 who underwent HCT (HCT group), and 23 who received no therapy (Untreated). All were followed starting before age 5 years. A sensitivity analysis restricted age of treatment below 3 years.

RESULTS

Survival was worse when comparing ERT versus HCT, and Untreated versus ERT. The cumulative incidences of hydrocephalus and cervical spinal cord compression were greater in ERT versus HCT. Findings persisted in the sensitivity analysis.

CONCLUSION

As newborn screening widens treatment opportunity for Hurler syndrome, this examination of early treatment quantifies some ERT benefit, supports presumptions about BBB impenetrability, and aligns with current guidelines to treat with HCT.

Neurocognitive and somatic stabilization in pediatric patients with severe Mucopolysaccharidosis Type I after 52 weeks of intravenous brain-penetrating insulin receptor antibody-iduronidase fusion protein (valanafusp alpha): an open label phase 1-2 trial

BACKGROUND

Mucopolysaccharidosis (MPS) Type I (MPSI) is caused by mutations in the gene encoding the lysosomal enzyme, α-L-iduronidase (IDUA), and a majority of patients present with severe neurodegeneration and cognitive impairment. Recombinant IDUA does not cross the blood-brain barrier (BBB). To enable BBB transport, IDUA was re-engineered as an IgG-IDUA fusion protein, valanafusp alpha, where the IgG domain targets the BBB human insulin receptor to enable transport of the enzyme into the brain. We report the results of a 52-week clinical trial on the safety and efficacy of valanafusp alpha in pediatric MPSI patients with cognitive impairment. In the phase I trial, 6 adults with attenuated MPSI were administered 0.3, 1, and 3 mg/kg doses of valanafusp alpha by intravenous (IV) infusion. In the phase II trial, 11 pediatric subjects, 2-15 years of age, were treated for 52 weeks with weekly IV infusions of valanafusp alpha at 1, 3, or 6 mg/kg. Assessments of adverse events, cognitive stabilization, and somatic stabilization were made. Outcomes at 52 weeks were compared to baseline.

RESULTS

Drug related adverse events included infusion related reactions, with an incidence of 1.7%, and transient hypoglycemia, with an incidence of 6.4%. The pediatric subjects had CNS involvement with a mean enrollment Development Quotient (DQ) of 36.1±7.1. The DQ, and the cortical grey matter volume of brain, were stabilized by valanafusp alpha treatment. Somatic manifestations were stabilized, or improved, based on urinary glycosaminoglycan levels, hepatic and spleen volumes, and shoulder range of motion.

CONCLUSION

Clinical evidence of the cognitive and somatic stabilization indicates that valanafusp alpha is transported into both the CNS and into peripheral organs due to its dual targeting mechanism via the insulin receptor and the mannose 6-phosphate receptor. This novel fusion protein offers a pharmacologic approach to the stabilization of cognitive function in MPSI.

TRIAL REGISTRATION

Clinical Trials.Gov, NCT03053089 . Retrospectively registered 9 February, 2017; Clinical Trials.Gov, NCT03071341 . Registered 6 March, 2017.

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.

Developmental and behavioral aspects of mucopolysaccharidoses with brain manifestations - Neurological signs and symptoms

The mucopolysaccharidoses (MPS) are a group of rare, inherited lysosomal storage disorders, caused by mutations in lysosomal enzymes involved in the degradation of glycosaminoglycans (GAGs). The resulting accumulation of GAGs in the body leads to widespread tissue and organ dysfunction. The spectrum, severity, and progression rate of clinical manifestations varies widely between and within the different MPS types. In addition to somatic signs and symptoms, which vary between the different MPS disorders, patients with MPS I, II, III, and VII present with significant neurological signs and symptoms, including impaired cognitive abilities, difficulties in language and speech, and/or behavioral and sleep problems. To effectively manage and develop therapies that target these neurological manifestations, it is of utmost importance to have a profound knowledge of their natural history and pathophysiology. This review describes the appearance and progression of neurological signs and symptoms in patients with MPS I, II, and III, based on presentations and discussions among an international group of experts during a meeting on the brain in MPS on April 28-30, 2016, and additional literature searches on this subject.

Assessments of neurocognitive and behavioral function in the mucopolysaccharidoses

The mucopolysaccharidoses (MPS) are a group of rare, inherited lysosomal storage disorders in which accumulation of glycosaminoglycans (GAGs) leads to progressive tissue and organ dysfunction. In addition to a variety of somatic signs and symptoms, patients with rapidly progressing MPS I (Hurler), II, III, and VII can present with significant neurological manifestations, including impaired cognitive abilities, difficulties in language and speech, behavioral abnormalities, sleep problems, and/or seizures. Neurological symptoms have a substantial impact on the quality of life of MPS patients and their families. Due to the progressive nature of cognitive impairment in these MPS patients, neurocognitive function is a sensitive indicator of disease progression, and a relevant outcome when testing efficacy of therapies for these disorders. In order to effectively manage and develop therapies that address neurological manifestations of MPS, it is important to use appropriate neurocognitive assessment tools that are sensitive to changes in neurocognitive function in MPS patients. This review discusses expert opinions on key issues and considerations for effective neurocognitive testing in MPS patients. In addition, it describes the neurocognitive assessment tools that have been used in clinical practice for these patients. The content of this review is based on existing literature and information from a meeting of international experts with extensive experience in managing and treating MPS disorders.

Quantitative neuroimaging in mucopolysaccharidoses clinical trials

The mucopolysaccharidosis (MPS) disorders are rare lysosomal storage disorders caused by mutations in lysosomal enzymes involved in glycosaminoglycan (GAG) degradation. The resulting intracellular accumulation of GAGs leads to widespread tissue and organ dysfunction. In addition to somatic signs and symptoms, patients with MPS can present with neurological manifestations such as cognitive decline, behavioral problems (e.g. hyperactivity and aggressiveness), sleep disturbances, and/or epilepsy. These are associated with significant abnormalities of the central nervous system (CNS), including white and gray matter lesions, brain atrophy, ventriculomegaly, and spinal cord compression. In order to effectively manage and develop therapies for MPS that target neurological disease, it is important to visualize and quantify these CNS abnormalities. This review describes optimal approaches for conducting magnetic resonance imaging assessments in multi-center clinical studies, and summarizes current knowledge from neuroimaging studies in MPS disorders. The content of the review is based on presentations and discussions on these topics that were held during a meeting of an international group of experts.

Practical management of behavioral problems in mucopolysaccharidoses disorders

The mucopolysaccharidosis (MPS) disorders are caused by deficiencies of specific lysosomal enzymes, resulting in progressive glycosaminoglycan (GAG) accumulation in cells and tissues throughout the body. Excessive GAG storage can lead to a variety of somatic manifestations as well as primary and secondary neurological symptoms. Behavioral problems (like hyperactivity, attention difficulties, and severe frustration) and sleeping problems are typical primary neurological symptoms of MPS caused by GAG accumulation in neurons, and are frequently observed in patients with MPS I, II, III, and VII. As these problems often place a significant burden on the family, proper management is important. This review summarizes current insights into behavioral and sleeping problems in MPS disorders and the most optimal management approaches, as presented and discussed during a meeting of an international group of experts with extensive experience in managing and treating MPS.

Epilepsy in mucopolysaccharidosis disorders

The mucopolysaccharidosis (MPS) disorders are caused by deficiencies of specific lysosomal enzymes involved in the catabolism of glycosaminoglycans (GAGs). The resulting GAG accumulation in cells and tissues throughout the body leads to progressive multi-organ dysfunction. MPS patients present with several somatic manifestations, including short stature, musculoskeletal abnormalities, and cardiorespiratory dysfunction, and several primary and secondary neurological signs and symptoms. Epileptic seizures are neurological signs of MPS thought to develop due to accumulation of GAGs in the brain, triggering alterations in neuronal connectivity and signaling, and release of inflammatory mediators. The amount of literature on the prevalence, pathophysiology, clinical features, and management of epileptic seizures in patients with MPS is limited. This review discusses current knowledge on this topic, as well as two case examples, presented and discussed during a closed meeting on MPS and the brain among an international group of experts with extensive experience in managing and treating MPS.

Intrathecal enzyme replacement therapy reverses cognitive decline in mucopolysaccharidosis type I

Mucopolysaccharidosis type I (MPS I) is an inherited lysosomal storage disease that seriously affects the brain. Severity of neurocognitive symptoms in attenuated MPS subtype (MPS IA) broadly varies partially, due to restricted permeability of blood‐brain barrier (BBB) which limits treatment effects of intravenously applied α‐L‐iduronidase (rhIDU) enzyme. Intrathecal (IT) rhIDU application as a possible solution to circumvent BBB improved brain outcomes in canine models; therefore, our study quantifies effects of IT rhIDU on brain structure and function in an MPS IA patient with previous progressive cognitive decline. Neuropsychological testing and MRIs were performed twice prior (baseline, at 1 year) and twice after initiating IT rhIDU (at 2nd and 3rd years). The difference between pre‐ and post‐treatment means was evaluated as a percentage of the change. Neurocognitive performance improved particularly in memory tests and resulted in improved school performance after IT rhIDU treatment. White matter (WM) integrity improved together with an increase of WM and corpus callosum volumes. Hippocampal and gray matter volume decreased which may either parallel reduction of glycosaminoglycan storage or reflect typical longitudinal brain changes in early adulthood. In conclusion, our outcomes suggest neurological benefits of IT rhIDU compared to the intravenous administration on brain structure and function in a single MPS IA patient. © 2017 The Authors. American Journal of Medical Genetics Part A Published by Wiley Periodicals, Inc.

Long-term cognitive and somatic outcomes of enzyme replacement therapy in untransplanted Hurler syndrome

Mucopolysaccharidosis type I (MPS I) was added to the Recommended Uniform Screening Panel for newborn screening in 2016, highlighting recognition that early treatment of MPS I is critical to stem progressive, irreversible disease manifestations. Enzyme replacement therapy (ERT) is an approved treatment for all MPS I phenotypes, but because the severe form (MPS IH, Hurler syndrome) involves rapid neurocognitive decline, the impermeable blood-brain-barrier is considered an obstacle for ERT. Instead, hematopoietic cell transplantation (HCT) has long been recommended, as it is believed to be the only therapy that arrests neurocognitive decline. Yet ERT monotherapy has never been compared to HCT, because it is unethically unacceptable to evaluate a therapeutic alternative to one shown to treat Central Nervous System (CNS) disease. An unusual opportunity to address this question is presented with this clinical report of a 16-year-old female with MPS IH treated only with ERT since her diagnosis at age 2. Neurological functioning was stable until cervical spinal cord compression at age 8, hydrocephalus at age 11, and neurocognitive declines beginning at age 10. Somatic disease burden is significant for first degree AV block, restrictive lung disease, bilateral hearing loss, severe corneal clouding, joint pain/limitations requiring mobility assistance, and short stature. This patient's extended survival and prolonged intact neurocognitive functioning depart from the untreated natural history of MPS IH. Disease burden typically controlled by HCT emerged. Although not anticipated to provide benefit for CNS disease, ERT may have provided some amelioration or slowing of neurocognitive deterioration.

Social Functioning and Behaviour in Mucopolysaccharidosis IH [Hurlers Syndrome]

BACKGROUND

Mucopolysaccharidosis type IH (MPS-IH) [Hurlers Syndrome] is a developmental genetic disorder characterised by severe physical symptoms and cognitive decline. This study aimed to investigate the behavioural phenotype of MPS-IH treated by haematopoietic cell transplantation, focusing on social functioning and sleep. Parental stress was also measured.

METHODS

Participants were 22 children with MPS-IH (mean age 9 years 1 month), of whom 10 were male (45%). Parents completed the Social Responsiveness Scale (SRS), Child Behaviour Checklist (CBCL), Children's Sleep Habit Questionnaire and Parent Stress Index, Short Form (PSI-SF).

RESULTS

Twenty-three per cent of children with MPS-IH scored in the severe range of the SRS, suggesting significant difficulties in social functioning. Children with MPS-IH were more than 30 times more likely to receive scores in the severe range than typically developing children. Thirty-six per cent scored in the mild-to-moderate range, suggesting milder, but marked, difficulties in social interaction. Although children with MPS-IH did not show significantly higher rates of internalising, externalising or total behaviour problems than the normative sample, they received scores that were significantly higher on social, thought and attention problems and rule-breaking behaviour, and all the competence areas of the CBCL. Parents of children with MPS-IH did not score significantly higher on parental stress than parents in a normative sample.

CONCLUSIONS

Parents of children with MPS-IH rate their children as having problems with social functioning and various areas of competence more frequently than previously thought, with implications for clinical support.

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

Sensitive, reliable measurement instruments are critical for the evaluation of disease progression and new treatments that affect the brain in the mucopolysaccharidoses (MPS). MPS I, II, and III have early onset clinical phenotypes that affect the brain during development and result in devastating cognitive decline and ultimately death without treatment. Comparisons of outcomes are hindered by diverse protocols and approaches to assessment including applicability to international trials necessary in rare diseases. We review both cognitive and adaptive measures with the goal of providing evidence to a Delphi panel to come to a consensus about recommendations for clinical trials for various age groups. The results of the consensus panel are reported in an accompanying article. The following data were gathered (from internet resources and from test manuals) for each measure and summarized in the discussion: reliability, validity, date and adequacy of normative data, applicability of the measure's metrics, cross cultural validity including translations and adaptations, feasibility in the MPS population, familiarity to sites, sensitivity to change, and interpretability. If, resulting from this consensus, standard protocols are used for both natural history and treatment studies, patients, their families, and health care providers will benefit from the ability to compare study outcomes.

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.