Mucopolysaccharidosis I: management and treatment guidelines

Causes of death in mucopolysaccharidoses

Mucopolysaccharidoses are inherited metabolic diseases caused by mutations in genes encoding enzymes required for degradation of glycosaminoglycans. A lack or severe impairment of activity of these enzymes cause accumulation of GAGs which is the primary biochemical defect. Depending on the kind of the deficient enzyme, there are 12 types and subtypes of MPS distinguished. Despite the common primary metabolic deficit (inefficient GAG degradation), the course and symptoms of various MPS types can be different, though majority of the diseases from the group are characterized by severe symptoms and significantly shortened live span. Here, we analysed the frequency of specific, direct causes of death of patients with different MPS types, the subject which was not investigated comprehensively to date. We examined a total of 1317 cases of death among MPS patients, including 393 cases of MPS I, 418 cases of MPS II, 232 cases of MPS III, 45 cases of MPS IV, 208 cases of MPS VI, and 22 cases of MPS VII. Our analyses indicated that the most frequent causes of death differ significantly between MPS types, with cardiovascular and respiratory failures being predominant in MPS I, MPS II, and MPS VI, neurological deficits in MPS III, respiratory issues in MPS IV, and hydrops fetalis in MPS VII. Results of such studies suggest what specific clinical problems should be considered with the highest priority in specific MPS types, apart from attempts to correct the primary causes of the diseases, to improve the quality of life of patients and to prolong their lives.

Viral-mediated gene therapy in pediatric neurological disorders

BACKGROUND

Due to the broad application of next-generation sequencing, the molecular diagnosis of genetic disorders in pediatric neurology is no longer an unachievable goal. However, treatments for neurological genetic disorders in children remain primarily symptomatic. On the other hand, with the continuous evolution of therapeutic viral vectors, gene therapy is becoming a clinical reality. From this perspective, we wrote this review to illustrate the current state regarding viral-mediated gene therapy in childhood neurological disorders.

DATA SOURCES

We searched databases, including PubMed and Google Scholar, using the keywords "adenovirus vector," "lentivirus vector," and "AAV" for gene therapy, and "immunoreaction induced by gene therapy vectors," "administration routes of gene therapy vectors," and "gene therapy" with "NCL," "SMA," "DMD," "congenital myopathy," "MPS" "leukodystrophy," or "pediatric metabolic disorders". We also screened the database of ClinicalTrials.gov using the keywords "gene therapy for children" and then filtered the results with the ones aimed at neurological disorders. The time range of the search procedure was from the inception of the databases to the present.

RESULTS

We presented the characteristics of commonly used viral vectors for gene therapy for pediatric neurological disorders and summarized their merits and drawbacks, the administration routes of each vector, the research progress, and the clinical application status of viral-mediated gene therapy on pediatric neurological disorders.

CONCLUSIONS

Viral-mediated gene therapy is on the brink of broad clinical application. Viral-mediated gene therapy will dramatically change the treatment pattern of childhood neurological disorders, and many children with incurable diseases will meet the dawn of a cure. Nevertheless, the vectors must be optimized for better safety and efficacy.

Early skeletal outcomes after hematopoietic stem and progenitor cell gene therapy for Hurler syndrome

Mucopolysaccharidosis type I Hurler (MPSIH) is characterized by severe and progressive skeletal dysplasia that is not fully addressed by allogeneic hematopoietic stem cell transplantation (HSCT). Autologous hematopoietic stem progenitor cell-gene therapy (HSPC-GT) provides superior metabolic correction in patients with MPSIH compared with HSCT; however, its ability to affect skeletal manifestations is unknown. Eight patients with MPSIH (mean age at treatment: 1.9 years) received lentiviral-based HSPC-GT in a phase 1/2 clinical trial (NCT03488394). Clinical (growth, measures of kyphosis and genu velgum), functional (motor function, joint range of motion), and radiological [acetabular index (AI), migration percentage (MP) in hip x-rays and MRIs and spine MRI score] parameters of skeletal dysplasia were evaluated at baseline and multiple time points up to 4 years after treatment. Specific skeletal measures were retrospectively compared with an external cohort of HSCT-treated patients. At a median follow-up of 3.78 years after HSPC-GT, all patients treated with HSPC-GT exhibited longitudinal growth within WHO reference ranges and a median height gain greater than that observed in patients treated with HSCT after 3-year follow-up. Patients receiving HSPC-GT experienced complete and earlier normalization of joint mobility compared with patients treated with HSCT. Mean AI and MP showed progressive decreases after HSPC-GT, suggesting a reduction in acetabular dysplasia. Typical spine alterations measured through a spine MRI score stabilized after HSPC-GT. Clinical, functional, and radiological measures suggested an early beneficial effect of HSPC-GT on MPSIH-typical skeletal features. Longer follow-up is needed to draw definitive conclusions on HSPC-GT's impact on MPSIH skeletal dysplasia.

The top 100 most cited articles on mucopolysaccharidoses: a bibliometric analysis

Background: Bibliometrics can trace general research trends in a particular field. Mucopolysaccharidoses (MPS), as a group of rare genetic diseases, seriously affect the quality of life of patients and their families. Scholars have devoted themselves to studying MPS's pathogenesis and treatment modalities and have published many papers. Therefore, we conducted a bibliometric and visual study of the top 100 most highly cited articles to provide researchers with an indication of the current state of research and potential directions in the field. Methods: The Web of Science Core Collection was searched for articles on MPS from 1 January 1900, to 8 November 2023, and the top 100 most cited articles were screened. The title, year of publication, institution, country, and first author of the articles were extracted and statistically analyzed using Microsoft Excel 2007. Keyword co-occurrence and collaborative networks were analyzed using VOSviewer 1.6.16. Results: A total of 9,273 articles were retrieved, and the top 100 most cited articles were filtered out. The articles were cited 18,790 times, with an annual average of 188 citations (122-507). Forty-two journals published these articles, with Molecular Genetics and Metabolism and Proceedings of the National Academy of Sciences of the United States being the most published journal (N = 8), followed by Pediatrics (N = 7), Blood (N = 6). The United States (N = 68), the UK (N = 25), and Germany (N = 20) were the top contributing countries. The Royal Manchester Children's Hospital (N = 20) and the University of North Carolina (N = 18) were the most contributing institutions. Muenzer J was the most prolific author (N = 14). Conclusion: We conducted a bibliometric and visual analysis of the top 100 cited articles in MPS. This study identifies the most influential articles currently available in the field of MPS, which provides a good basis for a better understanding of the disease and informs future research directions.

α-L-iduronidase fused with humanized anti-human transferrin receptor antibody (lepunafusp alfa) for mucopolysaccharidosis type I: A phase 1/2 trial

Mucopolysaccharidosis type I (MPS I) causes systemic accumulation of glycosaminoglycans due to a genetic deficiency of α-L-iduronidase (IDUA), which results in progressive systemic symptoms affecting multiple organs, including the central nervous system (CNS). Because the blood-brain barrier (BBB) prevents enzymes from reaching the brain, enzyme replacement therapy is effective only against the somatic symptoms. Hematopoietic stem cell transplantation can address the CNS symptoms, but the risk of complications limits its applicability. We have developed a novel genetically modified protein consisting of IDUA fused with humanized anti-human transferrin receptor antibody (lepunafusp alfa; JR-171), which has been shown in nonclinical studies to be distributed to major organs, including the brain, bringing about systemic reductions in heparan sulfate (HS) and dermatan sulfate concentrations. Subsequently, a first-in-human study was conducted to evaluate the safety, pharmacokinetics, and exploratory efficacy of JR-171 in 18 patients with MPS I. No notable safety issues were observed. Plasma drug concentration increased dose dependently and reached its maximum approximately 4 h after the end of drug administration. Decreased HS in the cerebrospinal fluid suggested successful delivery of JR-171 across the BBB, while suppressed urine and serum concentrations of the substrates indicated that its somatic efficacy was comparable to that of laronidase.

Mucopolysaccharidosis type VII (Sly syndrome) - What do we know?

Mucopolysaccharidosis type VII (MPS VII) is an ultra-rare, life-threatening, progressive disease caused by genetic mutations that affect lysosomal storage/function. MPS VII has an estimated prevalence of <1:1,000,000 and accounts for <3% of all MPS diagnoses. Given the rarity of MPS VII, comprehensive information on the disease is limited and we present a review of the current understanding. In MPS VII, intracellular glycosaminoglycans accumulate due to a deficiency in the lysosomal enzyme that is responsible for their degradation, β-glucuronidase, which is encoded by the GUSB gene. MPS VII has a heterogeneous presentation. Features can manifest across multiple systems and can vary in severity, age of onset and progression. The single most distinguishing clinical feature of MPS VII is non-immune hydrops fetalis (NIHF), which presents during pregnancy. MPS VII usually presents within one month of life and become more prominent at 3 to 4 years of age; key features are skeletal deformities, hepatosplenomegaly, coarse facies, and cognitive impairment, although phenotypic variation is a hallmark. Current treatments include hematopoietic stem cell transplantation and enzyme replacement therapy with vestronidase alfa. Care should be individualized for each patient. Development of consensus guidelines for MPS VII management and treatment is needed, as consolidation of expert knowledge and experience (for example, through the MPS VII Disease Monitoring Program) may provide a significant positive impact to patients.

Natural history of cardiac findings in mucopolysaccharidosis type I: report from an international registry

Mucopolysaccharidosis type I is an inborn error of glycosaminoglycan catabolism with phenotypes ranging from severe (Hurler syndrome) to attenuated (Hurler-Scheie and Scheie syndromes). Cardiovascular involvement is common and contributes significantly to morbidity and mortality. We conducted a retrospective analysis of the prevalence and natural history of cardiac abnormalities in treatment-naïve individuals enrolled in the international Mucopolysaccharidosis Type I Registry. Interrogation of echocardiography data (presence of cardiac valve regurgitation and/or stenosis; measurements of left ventricular chamber dimensions in diastole and systole, diastolic left ventricular posterior wall and interventricular septal thicknesses and ventricular systolic function (shortening fraction)) showed that mitral regurgitation was the most common and earliest finding for individuals with both severe (58.3%, median age 1.2 years) and attenuated (74.2%, median age 8.0 years) disease. Left-sided valve stenosis was also common in individuals with attenuated disease (mitral 30.3%; aortic 25%). Abnormal ventricular wall and septal thickness (Z-scores ≥2) were observed early in both phenotypes. Z-scores for diastolic left ventricular posterior wall and interventricular septal thicknesses increased with age in the severe phenotype (annualised slopes of 0.2777 [p = 0.037] and 0.3831 [p = 0.001], respectively); a similar correlation was not observed in the attenuated phenotype (annualised slopes of -0.0401 [p = 0.069] and -0.0029 [p = 0.875], respectively). Decreased cardiac ventricular systolic function (defined as shortening fraction <28%) was uncommon but, when noted, was more frequent in infants with the severe phenotype. While cardiac abnormalities occur early in both severe and attenuated mucopolysaccharidosis type I, the pattern of valve dysfunction and progression of ventricular abnormalities vary by phenotype.

Mucopolysaccharidosis type I Hurler-Scheie syndrome: a case report

Introduction and importance

Hurler syndrome, also known as mucopolysaccharidoses type I, is a rare autosomal recessive lysosomal storage disorder with decreased activities of α-L iduronidase, resulting in the accumulation of glycosaminoglycans (GAGs) within various tissues.

Case presentation

The authors presented a case report of a 15-year-old male who presented with a lower respiratory tract infection and was admitted to the pediatrics department with a history of facial dysmorphism, skeletal abnormalities, and corneal clouding and below-normal cognitive function which is consistent with the Hurler-Scheie syndrome. Skeletal abnormalities include inverted j-shaped sella turcica, bullet-shaped phalanges, thoracolumbar kyphosis, and acetabular dysplasia.

Clinical discussion

Mucopolysaccharidosis I is classically divided into three syndromes, that is, Hurler syndrome (the severe form), Hurler-Scheie syndrome (the intermediate form), and Scheie syndrome (the attenuated form). Most of a doctor's first diagnosis is based on their observation of the signs and symptoms.

Conclusion

Early disease diagnosis, genetic counseling, and regular follow-up with recent treatment modalities can reduce mortality significantly and improve the child's health status.

The importance of skeletal x-ray screening for dysostosis multiplex in the early diagnosis of mucopolysaccharidosis

PURPOSE

Our aim is the early detection of mucopolysaccharidosis (MPS) by examining the radiographs taken for reasons other than a metabolic disease, such as infection, trauma, and short stature.

METHODS

The radiographs of children who applied to outpatient and emergency clinics in our hospital between 01/01/2022 and 31/12/2022 were examined by a pediatric radiologist retrospectively without knowledge of patient information. The MPS enzyme panel and urine glycosaminoglycan analysis were performed in patients having dysostosis multiplex on radiographs. In cases with MPS detected by enzyme and urine analysis, the definitive diagnosis was confirmed by genetic analysis.

RESULTS

Skeletal radiographs of 15.104 cases admitted to our hospital were examined (11,270 chest x-ray, 314 lumbosacral spine x-ray, 2970 hand x-ray, 253 pelvis x-ray, 162 skull x-ray, and 135 complete skeletal surveys). In 67 children, dysostosis multiplex was observed in the skeletal X-ray. Among them, seven newly diagnosed MPS cases were detected. Three cases were diagnosed with MPS type 4A, two with MPS type 6, one with MPS type 2 and one with MPS type 3B. Age at diagnosis was 46.2 ± 30.6 months (range; 20-111 months). There was a history of consanguinity in 6 (85.7%) cases.

CONCLUSION

Radiographs can provide clues for diagnosing MPS before the clinical findings become prominent in children admitted to the hospital for other complaints. Therefore, X-ray screening can be performed on children in endemic regions of MPS to search for dysostosis multiplex.

Hurler Syndrome Glycosaminoglycans Decrease in Cerebrospinal Fluid without Brain-Targeted Therapy

Novel therapies for Hurler syndrome aim to cross the blood-brain barrier (BBB) to target neurodegeneration by degrading glycosaminoglycans (GAG). BBB penetration has been assumed with decreased cerebrospinal fluid (CSF) GAG, yet little is known about CSF GAG without brain-targeting therapies. We compared pre-transplant CSF GAG in patients who were treatment naïve (n = 19) versus receiving standard non-BBB penetrating enzyme replacement therapy (ERT, n = 12). In the ERT versus treatment naïve groups, CSF GAG was significantly lower across all content assayed, raising questions about using CSF GAG decrements to show BBB penetration. Future studies should compare GAG reduction in standard versus novel therapies. ANN NEUROL 2023;94:1182-1186.

First Three Years' Experience of Mucopolysaccharidosis Type-I Newborn Screening in California

OBJECTIVE

To report on the first 3 years of mucopolysaccharidosis type I (MPS I) newborn screening (NBS) in the large and diverse state of California.

STUDY DESIGN

The California Genetic Disease Screening Program began universal NBS for MPS I on August 29, 2018. The screening uses a 2-tiered approach: an α-L-iduronidase (IDUA) enzyme activity assay followed by DNA sequencing for variants in the IDUA gene.

RESULTS

As of August 29, 2021, 1 295 515 California newborns were screened for MPS I. In tier 1 of screening, 329 (0.025%) had an IDUA enzyme measurement below the cutoff and underwent tier-2 IDUA DNA sequencing. After tier 2, 146 (0.011%) newborns were screen positive, all of whom were referred to a metabolic Special Care Center for follow-up. After long-term follow-up, 7 cases were resolved as severe MPS I (Hurler syndrome) and 2 cases as attenuated MPS I for an MPS I birth prevalence of 1/143 946. DNA sequencing identified 107 unique IDUA variants among a total of 524 variants; 65% were known pseudodeficiency alleles, 25% were variants of uncertain significance, and 10% were pathogenic variants.

CONCLUSIONS

As a result of a 2-tiered NBS approach, 7 newborns diagnosed with Hurler syndrome had received early treatment for MPS I. Continuation of California's long-term follow-up program will be crucial for further understanding the complex genotype-phenotype relationships of MPS I.

Mucopolysaccharidosis Type I: The Importance of Early Diagnosis for Adequate Treatment

Mucopolysaccharidoses are rare lysosomal storage disorders in which glycosaminoglycans accumulate in tissues, causing multiorgan dysfunction. Mucopolysaccharidosis type I is an autosomal recessive disease caused by a deficiency of the enzyme alpha-L-iduronidase, resulting in the accumulation of dermatan and heparan sulfate. Early diagnosis is crucial for early treatment and improved outcomes. We report the case of a female child with classic clinical features who was diagnosed early which allowed hematopoietic stem cell transplantation and slowed disease progression. She presented at birth with linea alba and umbilical and inguinal hernias. Since the first months of life, she had recurrent respiratory infections. At nine months, a motor delay was noticed, and at 20 months, craniosynostosis was corrected with surgery. Coarse facial features, thoracolumbar kyphosis, and hepatomegaly prompted a urinary glycosaminoglycan study at 22 months, which showed elevated levels. Alfa-L-iduronidase activity in dried blood spot testing was low, compatible with mucopolysaccharidosis type I. Molecular testing of gene IDUA, performed for genetic counseling, revealed the pathogenic variants c.1205G>A (p.Trp402Ter) and c.1598C>G (p.Pro533Arg) in compound heterozygosity. At 26 months, her development quotient was average for her age. She started enzyme replacement therapy at 29 months and underwent hematopoietic stem cell transplantation at 33 months, which softened the coarse features, reduced respiratory infections, and improved hepatomegaly. However, at age five, her development quotient was 76 (mean = 100, standard deviation = 15). This intellectual impairment might have been prevented with an earlier diagnosis and treatment.

Glia Cells Control Olfactory Neurogenesis by Fine-Tuning CXCL12

Olfaction depends on lifelong production of sensory neurons from CXCR4 expressing neurogenic stem cells. Signaling by CXCR4 depends on the concentration of CXCL12, CXCR4's principal ligand. Here, we use several genetic models to investigate how regulation of CXCL12 in the olfactory stem cell niche adjusts neurogenesis. We identify subepithelial tissue and sustentacular cells, the olfactory glia, as main CXCL12 sources. Lamina propria-derived CXCL12 accumulates on quiescent gliogenic stem cells via heparan sulfate. Additionally, CXCL12 is secreted within the olfactory epithelium by sustentacular cells. Both sustentacular-cell-derived and lamina propria-derived CXCL12 are required for CXCR4 activation. ACKR3, a high-affinity CXCL12 scavenger, is expressed by mature glial cells and titrates CXCL12. The accurate adjustment of CXCL12 by ACKR3 is critical for CXCR4-dependent proliferation of neuronal stem cells and for proper lineage progression. Overall, these findings establish precise regulation of CXCL12 by glia cells as a prerequisite for CXCR4-dependent neurogenesis and identify ACKR3 as a scavenger influencing tissue homeostasis beyond embryonic development.

Phenotypic characterisation of the Mucopolysaccharidosis Type I (MPSI) Idua-W392X mouse model reveals increased anxiety-related traits in female mice

Mucopolysaccharidosis Type I (MPSI) is a rare inherited lysosomal storage disease that arises due to mutations in the IDUA gene. Defective alpha-L-iduronidase (IDUA) enzyme is unable to break down glucosaminoglycans (GAGs) within the lysosomes and, as a result, there is systemic accumulation of undegraded products in lysosomes throughout the body leading to multi-system disease. Here, we characterised the skeletal/craniofacial, neuromuscular and behavioural outcomes of the MPSI Idua-W392X mouse model. We demonstrate that Idua-W392X mice have gross craniofacial abnormalities, showed signs of kyphosis, and show signs of hypoactivity compared to wild-type mice. X-ray imaging analysis revealed significantly shorter and wider tibias and femurs, significantly wider snouts, increased skull width and significantly thicker zygomatic arch bones in Idua-W392X female mice compared to wild-type mice at 9 and 10.5 months of age. Idua-W392X mice display decreased muscle strength, especially in the forelimbs, which is already apparent from 3 months of age. Female Idua-W392X mice display hypoactivity in the open-field test from 9 months of age and anxiety-like behaviour at 10 months of age. As these behaviours have been identified in Hurler children, the MPSI Idua-W392X mouse model may be important for the investigation of new therapeutic approaches for MPSI-Hurler.

Posterior Fossa Horns in Hurler Syndrome: Prevalence and Regression

Posterior fossa "horns" caused by internal hypertrophy of the occipitomastoid sutures are one of the more recently defined cranial abnormalities described in mucopolysaccharidoses, especially in Hurler Syndrome. However, details of this finding, including the development and natural history, are not well-understood. Two hundred eighty-six brain MR imaging studies of 61 patients with mucopolysaccharidosis I-Hurler syndrome treated at single institution between 1996 and 2015 were studied. Posterior fossa horn height was measured as the perpendicular distance from the tip of the horn to the expected curvature of the occipital inner table. Fifty-seven of the 61 patients (93.4%) had evidence of posterior fossa horns on at least one occasion. The initial average height of the right horn was 4.5 mm, and the left horn, 4.7 mm. Most of the posterior horns regressed before transplantation in our cohort, though the exact age was variable among the patients. Nearly all patients in our cohort had posterior fossa horns, and these horns regressed with age. The regression of the horns frequently started before transplantation. This trend has not been previously described, and it may suggest unknown effects of mucopolysaccharidosis on skull development.

An Innovative Tool for Evidence-Based, Personalized Treatment Trials in Mucopolysaccharidosis

Mucopolysaccharidosis (MPS) is a group of rare metabolic diseases associated with reduced life expectancy and a substantial unmet medical need. Immunomodulatory drugs could be a relevant treatment approach for MPS patients, although they are not licensed for this population. Therefore, we aim to provide evidence justifying fast access to innovative individual treatment trials (ITTs) with immunomodulators and a high-quality evaluation of drug effects by implementing a risk-benefit model for MPS. The iterative methodology of our developed decision analysis framework (DAF) consists of the following steps: (i) a comprehensive literature analysis on promising treatment targets and immunomodulators for MPS; (ii) a quantitative risk-benefit assessment (RBA) of selected molecules; and (iii) allocation phenotypic profiles and a quantitative assessment. These steps allow for the personalized use of the model and are in accordance with expert and patient representatives. The following four promising immunomodulators were identified: adalimumab, abatacept, anakinra, and cladribine. An improvement in mobility is most likely with adalimumab, while anakinra might be the treatment of choice for patients with neurocognitive involvement. Nevertheless, a RBA should always be completed on an individual basis. Our evidence-based DAF model for ITTs directly addresses the substantial unmet medical need in MPS and characterizes a first approach toward precision medicine with immunomodulatory drugs.

Mucopolysaccharidosis Type I in Mexico: Case-Based Review

INTRODUCTION

Mucopolysaccharidosis type I (MPS I) is a lysosomal storage disease present in 1:100,000 newborns. Variants in the IDUA (alpha-L-iduronidase) gene decrease the enzyme activity for glycosaminoglycans metabolism. MPS I patients exhibit clinical manifestations that fall on the Hurler, Hurler-Scheie, and Scheie syndrome spectrum.

CASE PRESENTATION

We present a male Mexican patient with respiratory exacerbations requiring recurrent hospitalizations. He showed macrocephaly, coarse facies, hepatomegaly, umbilical hernia, and dorsal kyphosis. The sequencing of the IDUA gene revealed the following genotype: c.46_57del12/c.1205G>A. He received combined therapy with hematopoietic stem cell transplantation and enzyme replacement. Mexican case reports were analyzed to estimate the prevalence of the associated genetic variants.

CONCLUSION

Despite the challenges of managing this rare disease in Mexico, our patient benefited from the combined therapy. The discrete clinical manifestations and prompt evaluation by a geneticist were crucial in establishing a diagnosis, enabling an early intervention by a multidisciplinary team. The combination of ERT before and after HSCT provided health benefits to our patient.

Long term follow-up after haematopoietic stem cell transplantation for mucopolysaccharidosis type I-H: a retrospective study of 51 patients

Mucopolysaccharidosis type I-H (MPS I-H) is a rare lysosomal storage disorder caused by α-L-Iduronidase deficiency. Early haematopoietic stem cell transplantation (HSCT) is the sole available therapeutic option to preserve neurocognitive functions. We report long-term follow-up (median 9 years, interquartile range 8-16.5) for 51 MPS I-H patients who underwent HSCT between 1986 and 2018 in France. 4 patients died from complications of HSCT and one from disease progression. Complete chimerism and normal α-L-Iduronidase activity were obtained in 84% and 71% of patients respectively. No difference of outcomes was observed between bone marrow and cord blood stem cell sources. All patients acquired independent walking and 91% and 78% acquired intelligible language or reading and writing. Intelligence Quotient evaluation (n = 23) showed that 69% had IQ ≥ 70 at last follow-up. 58% of patients had normal or remedial schooling and 62% of the 13 adults had good socio-professional insertion. Skeletal dysplasia as well as vision and hearing impairments progressed despite HSCT, with significant disability. These results provide a long-term assessment of HSCT efficacy in MPS I-H and could be useful in the evaluation of novel promising treatments such as gene therapy.

Triamterene Functions as an Effective Nonsense Suppression Agent for MPS I-H (Hurler Syndrome)

Mucopolysaccharidosis I-Hurler (MPS I-H) is caused by the loss of α-L-iduronidase, a lysosomal enzyme that degrades glycosaminoglycans. Current therapies cannot treat many MPS I-H manifestations. In this study, triamterene, an FDA-approved, antihypertensive diuretic, was found to suppress translation termination at a nonsense mutation associated with MPS I-H. Triamterene rescued enough α-L-iduronidase function to normalize glycosaminoglycan storage in cell and animal models. This new function of triamterene operates through premature termination codon (PTC) dependent mechanisms that are unaffected by epithelial sodium channel activity, the target of triamterene's diuretic function. Triamterene represents a potential non-invasive treatment for MPS I-H patients carrying a PTC.

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.

Dry synovitis, a rare entity distinct from juvenile idiopathic arthritis

BACKGROUND

Dry synovitis (DS) is a rare entity as only a few cases have been reported to date. We describe the clinical features, radiological manifestations and course of DS in comparison with rheumatoid factor negative polyarticular juvenile idiopathic arthritis (RFneg-polyJIA).

METHODS

We performed a multicenter retrospective collection of data of DS patients who presented with progressive joint limitations without palpable synovitis, absence of elevated acute phase reactants, negative ANA and RF, and imaging showing joint and/or osteochondral involvement. For comparative purposes, we included a cohort of RF neg-polyJIA patients.

RESULTS

Twelve DS patients, 8F/4 M, with mean age at onset of 6.1 years, were included. Presenting signs comprised delayed motor development, functional limitations and/or progressive stiffness. Clinical examination showed symmetric polyarticular involvement with variable muscular atrophy. MRI showed mild, diffuse synovial involvement, without effusion. With time, signs of progressive osteochondral damage became evident, despite treatment. All patients were treated with low-dose corticosteroids and methotrexate. Anti-TNF agents were prescribed in five. The response was variable with limited joint mobility in 11/12, and need of joint replacement in 2. In comparison with a cohort of RFneg-polyJIA, DS patients presented higher number of joint involved (p = 0.0001) and contractures (p = 0.0001), less swelling (p = 0.0001) and prolonged diagnostic delay (p = 0.0001).

CONCLUSION

DS represents a unique juvenile-onset arthropathy, distinct from polyarticular JIA. Awareness among pediatricians is essential for early recognition and proper treatment. Further studies, including synovial pathology, immunology and genetics may contribute to a better understanding of this rare disorder of childhood.

How to Distinguish Attenuated Forms of Mucopolysaccharidosis and Articular Forms of Juvenile Arthritis: Development of Diagnostic Algorithm Based on the Data from Multicenter Retrospective Study

Background. Differential diagnosis of attenuated forms of mucopolysaccharidosis (MPS) and juvenile idiopathic arthritis (JIA) can be challenging due to their similarities. Objective. The aim of the study is to create simple diagnostic criteria (DScore) that would allow to differentiate MPS from JIA for earlier MPS diagnosis. Methods. The retrospective multicenter study included analysis of clinical (joint, heart, eye involvement, hearing loss, hernias, psychomotor delay, noisy breathing, posture disorders, macrocephaly, hepatomegaly, splenomegaly, and growth delay) and laboratory data (ESR, CRP, hemoglobin, WBC, and platelets) from MPS patients (n = 41) and from rheumatoid factor-negative polyarticular category of JIA patients (n = 255). These variables allowed to differentiate both conditions and were used to create DScore. Results. Patients with MPS had younger onset age, male predominance, height and weight delay, lower inflammation markers (WBC, platelets, and ESR), and usually involved joints, especially cervical spine, upper limbs joints, hip, and small foot joints. The prevalence of eye involvement was similar for both diseases, however, the type of involvement was different. JIA patients had uveitis and its’ complications and MPS patients — corneal opacity and cataract. No differences in CRP levels were revealed in most cases. The major diagnostic criterion of MPS was the presence of more than one extra-articular manifestation associated with polyarticular involvement. DScore has included 5 following criteria: ESR ≤ 11 mm/h (38 points), height ≤ -2.0 SD (20 points), onset age of articular manifestations ≤ 1.1 year (24 points), male gender (15 points), and symmetrical limitation of movements in elbow joints (29 points). The sum > 38 points allowed us to differentiate MPS and JIA with sensitivity of 92.7% and specificity of 91.0%. Conclusion. This DScore can be used for differential diagnosis of mild MPS and JIA alongside with routine diagnostic procedures. DScore allows us to identify a group of patients with joint involvement who require MPS exclusion.

Dilated Optic Nerve Sheath in Mucopolysaccharidosis I: Common and Not Necessarily High Intracranial Pressure

Hydrocephalus is one of the earliest manifestations of mucopolysaccharidosis I-Hurler syndrome, and delayed treatment of hydrocephalus can lead to neurocognitive delay or even death. Optic nerve sheath diameter has been established as a noninvasive measurement to detect elevated intracranial pressure. This study aimed to establish correlations between optic nerve sheath diameter and opening pressure. Forty-nine MR images and opening pressures in patients with mucopolysaccharidosis I-Hurler syndrome were retrospectively reviewed from 2008 to 2020. The optic nerve sheath diameter was measured 3 mm posterior to the posterior margin of the globe (retrobulbar) and 10 mm anterior to the optic foramen (midpoint segment), and the average was taken between the 2 eyes. Opening pressure was measured with the patient in the lateral decubitus position with controlled end-tidal CO2 on the same day as the MR imaging. The average retrobulbar optic nerve sheath diameter was 5.33 mm, higher than the previously reported measurement in healthy controls, in patients with idiopathic intracranial hypertension, and there was a positive correlation between age and the optic nerve sheath diameter measured at the retrobulbar or midpoint segment (retrobulbar segment, R 2 = 0.27, P < .01; midpoint segment, R 2 = 0.20, P < .01). However, there was no correlation between retrobulbar or midpoint segment optic nerve sheath diameter and opening pressure (retrobulbar segment, R 2 = 0.02, P = .17; midpoint segment, R 2 = 0.03, P < .12). This study shows a higher average optic nerve sheath diameter in patients with mucopolysaccharidosis I-Hurler syndrome than in healthy controls regardless of the location of the measurement. However, the degree of optic nerve sheath dilation does not correlate with opening pressure, suggesting that increased optic nerve sheath diameter is an ocular manifestation of mucopolysaccharidosis I-Hurler syndrome itself rather than a marker of elevated intracranial pressure.

Hurler Syndrome: Orofacial Clinical Findings

Hurler syndrome (HS) belongs to the category of mucopolysaccharidosis (MPS), a spectrum of rare genetic disorders of the mucopolysaccharides metabolism. This syndrome is due to a defect in α-iduronidase, an enzyme responsible for the degradation of the glycosaminoglycans (GAGs) heparin and dermatan sulfate. Intra and extracellular accumulation of these non-metabolized substances may lead to multisystemic dysfunction, with severe stomatognathic involvement that may often need treatment. The aim of this article is to present the heterogeneity of orofacial and radiographic findings observed in two patients with HS with long-term follow-up, who were referred to our Stomatology department.

Left-sided valvular heart disease and retinopathy in a 38-year-old woman with attenuated mucopolysaccharidosis: a case report

Mucopolysaccharidoses (MPS) are a group of inherited lysosomal storage disorders caused by deficient levels and/or activity of glycosaminoglycan (GAG)-degradative enzymes. MPS are characterized by accumulation of the mucopolysaccharides heparan sulfate, dermatan sulfate, keratan sulfate, or chondroitin sulfate in tissues. We report the case of a 38-year-old woman with a history of joint restriction and retinitis pigmentosa who developed bivalvular heart failure requiring surgery. It was not until pathological examination of surgically excised valvular tissue that a diagnosis of MPS I was made. Her musculoskeletal and ophthalmologic symptoms, when placed in the context of MPS I, painted the diagnostic picture of a genetic syndrome that was overlooked until a diagnosis was made in late middle age.

Mucopolysaccharidosis: What Pediatric Rheumatologists and Orthopedics Need to Know

Mucopolysaccharidosis (MPS) is a group of disorders caused by the reduced or absent activity of enzymes involved in the glycosaminoglycans (GAGs) degradation; the consequence is the progressive accumulation of the substrate (dermatan, heparan, keratan or chondroitin sulfate) in the lysosomes of cells belonging to several tissues. The rarity, the broad spectrum of manifestations, the lack of strict genotype-phenotype association, and the progressive nature of MPS make diagnosing this group of conditions challenging. Musculoskeletal involvement represents a common and prominent feature of MPS. Joint and bone abnormalities might be the main clue for diagnosing MPS, especially in attenuated phenotypes; therefore, it is essential to increase the awareness of these conditions among the pediatric rheumatology and orthopedic communities since early diagnosis and treatment are crucial to reduce the disease burden of these patients. Nowadays, enzyme replacement therapy (ERT) and hematopoietic stem cell transplantation (HSCT) are available for some MPS types. We describe the musculoskeletal characteristics of MPS patients through a literature review of MPS cases misdiagnosed as having rheumatologic or orthopedic conditions.

First-in-human in vivo genome editing via AAV-zinc-finger nucleases for mucopolysaccharidosis I/II and hemophilia B

Zinc-finger nuclease (ZFN)-based in vivo genome editing is a novel treatment that can potentially provide lifelong protein replacement with single intravenous administration. Three first-in-human open-label ascending single-dose phase 1/2 studies were performed in parallel (starting November 2017) primarily to assess safety and tolerability of ZFN in vivo editing therapy in mucopolysaccharidosis I (MPS I) (n = 3), MPS II (n = 9), and hemophilia B (n = 1). Treatment was well tolerated with no serious treatment-related adverse events. At the 1e13 vg/kg dose, evidence of genome editing was detected through albumin-transgene fusion transcripts in liver for MPS II (n = 2) and MPS I (n = 1) subjects. The MPS I subject also had a transient increase in leukocyte iduronidase activity to the lower normal range. At the 5e13 vg/kg dose, one MPS II subject had a transient increase in plasma iduronate-2-sulfatase approaching normal levels and one MPS I subject approached mid-normal levels of leukocyte iduronidase activity with no evidence of genome editing. The hemophilia B subject was not able to decrease use of factor IX concentrate; genome editing could not be assessed. Overall, ZFN in vivo editing therapy had a favorable safety profile with evidence of targeted genome editing in liver, but no long-term enzyme expression in blood.

Clinical trials and promising preclinical applications of CRISPR/Cas gene editing

Treatment of genetic disorders by genomic manipulation has been the unreachable goal of researchers for many decades. Although our understanding of the genetic basis of genetic diseases has advanced tremendously in the last few decades, the tools developed for genomic editing were not efficient and practical for their use in the clinical setting until now. The recent advancements in the research of Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) and CRISPR-associated protein (Cas) systems offered an easy and efficient way to edit the genome and accelerated the research on their potential use in the treatment of genetic disorders. In this review, we summarize the clinical trials that evaluate the CRISPR/Cas systems for treating different genetic diseases and highlight promising preclinical research on CRISPR/Cas mediated treatment of a great diversity of genetic disorders. Ultimately, we discuss the future of CRISPR/Cas mediated genome editing in genetic diseases.

MPS VII - Extending the classical phenotype

Mucopolysaccharidosis VII (or Sly syndrome) is an autosomal recessive disorder characterised by a deficiency in the enzyme Beta-glucuronidase (GUSB). Partial degradation of glycosaminoglycans (GAGs); chondroitin sulfate (CS), dermatan sulfate (DS) and heparan sulfate (HS) results in the accumulation of these fragments in the lysosomes of many tissues, eventually leading to multisystem damage. In some cases, early diagnosis on clinical grounds alone can be difficult due to the extreme variability of the clinical presentation and disease progression. We present a case report of a 31-year-old male patient diagnosed with MPS VII at the age of 28, who multiple specialists saw without suspecting the diagnosis due to the unusual presentation. The patient presented with a history of developmental delay, scoliosis, kyphosis, corneal clouding, abnormal gait, short stature, hearing impairment, slightly coarse facial features and progressive deterioration of fine motor skills since childhood. The patient had inguinal hernia repair at around 12 months, bilateral hearing impairment with a left bone-anchored hearing aid, and spinal surgery. During spinal surveillance MPS VII was suspected by a spinal surgeon with interest in MPS, and the diagnosis confirmed with a deficiency in beta-glucuronidase in leucocytes and marginally elevated urinary GAGs. Next-generation sequencing identified two mutations in the GUSB gene (OMIM 611499), c.526C > T p.(Leu176Phe) and c.1820G > C p.(Gly607Ala). Although the patient exhibited features of the severe form of non-classical manifestations, his metabolic condition has remained reasonably stable, surviving into adulthood with only symptomatic treatment. We present the ever-expanding phenotypic spectrum of this ultra-rare disease.

Modern Approaches to the Management of Children with Mucopolysaccharidosis Type I

This article presents modern data on epidemiology, etiology, and clinical manifestations of mucopolysaccharidosis (MPS) type I in children. MPS develops due to deficiency of particular lysosomal enzyme which determines the disease type. The article considers in details disease's pathogenesis and classification. Evidence-based approaches to diagnosis (differential diagnosis included) are covered, moreover, special attention is paid to pathogenetic, symptomatic, and surgical treatment of MPS.

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.

MPSI Manifestations and Treatment Outcome: Skeletal Focus

Mucopolysaccharidosis type I (MPSI) (OMIM #252800) is an autosomal recessive disorder caused by pathogenic variants in the IDUA gene encoding for the lysosomal alpha-L-iduronidase enzyme. The deficiency of this enzyme causes systemic accumulation of glycosaminoglycans (GAGs). Although disease manifestations are typically not apparent at birth, they can present early in life, are progressive, and include a wide spectrum of phenotypic findings. Among these, the storage of GAGs within the lysosomes disrupts cell function and metabolism in the cartilage, thus impairing normal bone development and ossification. Skeletal manifestations of MPSI are often refractory to treatment and severely affect patients’ quality of life. This review discusses the pathological and molecular processes leading to impaired endochondral ossification in MPSI patients and the limitations of current therapeutic approaches. Understanding the underlying mechanisms responsible for the skeletal phenotype in MPSI patients is crucial, as it could lead to the development of new therapeutic strategies targeting the skeletal abnormalities of MPSI in the early stages of the disease.

Quantification of Idua Enzymatic Activity Combined with Observation of Phenotypic Change in Zebrafish Embryos Provide a Preliminary Assessment of Mutated idua Correlated with Mucopolysaccharidosis Type I

Mucopolysaccharidosis type I (MPS I) is an inherited autosomal recessive disease resulting from mutation of the α-l-Iduronidase (IDUA) gene. New unknown mutated nucleotides of idua have increasingly been discovered in newborn screening, and remain to be elucidated. In this study, we found that the z-Idua enzymatic activity of zebrafish idua-knockdown embryos was reduced, resulting in the accumulation of undegradable metabolite of heparin sulfate, as well as increased mortality and defective phenotypes similar to some symptoms of human MPS I. After microinjecting mutated z-idua-L346R, -T364M, -E398-deleted, and -E540-frameshifted mRNAs, corresponding to mutated human IDUA associated with MPS I, into zebrafish embryos, no increase in z-Idua enzymatic activity, except of z-idua-E540-frameshift-injected embryos, was noted compared with endogenous z-Idua of untreated embryos. Defective phenotypes were observed in the z-idua-L346R-injected embryos, suggesting that failed enzymatic activity of mutated z-Idua-L346R might have a dominant negative effect on endogenous z-Idua function. However, defective phenotypes were not observed in the z-idua-E540-frameshifted-mRNA-injected embryos, which provided partial enzymatic activity. Based on these results, we suggest that the z-Idua enzyme activity assay combined with phenotypic observation of mutated-idua-injected zebrafish embryos could serve as an alternative platform for a preliminary assessment of mutated idua not yet characterized for their role in MPS I.

Exosome- and extracellular vesicle-based approaches for the treatment of lysosomal storage disorders

Cell-generated extracellular vesicles (EVs) are being engineered as biologically-inspired vehicles for targeted delivery of therapeutic agents to treat difficult-to-manage human diseases, including lysosomal storage disorders (LSDs). Engineered EVs offer distinct advantages for targeted delivery of therapeutics compared to existing synthetic and semi-synthetic nanoscale systems, for example with regard to their biocompatibility, circulation lifetime, efficiencies in delivery of drugs and biologics to target cells, and clearance from the body. Here, we review literature related to the design and preparation of EVs as therapeutic carriers for targeted delivery and therapy of drugs and biologics with a focus on LSDs. First, we introduce the basic pathophysiology of LDSs and summarize current approaches to diagnose and treat LSDs. Second, we will provide specific details about EVs, including subtypes, biogenesis, biological properties and their potential to treat LSDs. Third, we review state-of-the-art approaches to engineer EVs for treatments of LSDs. Finally, we summarize explorative basic research and applied applications of engineered EVs for LSDs, and highlight current challenges, and new directions in developing EV-based therapies and their potential impact on clinical medicine.

Assessment, pharmacological therapy and rehabilitation management of musculoskeletal pain in children with mucopolysaccharidoses: a scoping review

Background

Pain of musculoskeletal origin is very common in young patients affected by Mucopolysaccharidoses. This scoping review evaluates the evidence for assessment, pharmacological treatment and rehabilitation management for musculoskeletal pain of the latter.

Methods

A Medline search through PubMed has been performed for studies published in English at least for the past twenty years. Two investigators independently reviewed all search results and extracted those that met the inclusion criteria.

Results

29 studies have been selected and analysed in depth, of which 10 related to pain assessment, 11 concerned pharmacological approach, and 8 reported rehabilitation approaches.

Conclusion

Few data are available in literature concerning the classification and management of pain in children with Mucopolysaccharidoses. Notwithstanding, pain evaluation methods are effectively used to classify pain intensity, according to the age group and communication abilities of young Mucopolysaccharidoses patients. The review emphasizes that drug therapies have a palliative purpose, while rehabilitation reduces musculoskeletal pain and can provide a therapeutic effect on disabilities.

Deposition keratopathy

Material can be deposited in the cornea as a result of a wide range of systemic and ophthalmic diseases, as well as local and systemic therapies. Causes include local infection or trauma, systemic malignancy, a wide range of medications and a host of genetic and metabolic diseases. Some of these can be acutely life threatening, so generalists caring for both children and adults should have a basic awareness of the pattern and distribution of corneal deposits to facilitate timely diagnosis, investigation, management or onward referral to avoid significant morbidity or mortality. This article outlines causes of corneal deposits found in patients presenting to primary care, ophthalmic clinics or encountered on the wards to help generalists avoid missing serious pathology. It also provides insight into the natural history of underlying causative conditions and their possible treatments.

Hematopoietic Stem Cell Transplantation for Neurological Disorders: A Focus on Inborn Errors of Metabolism

Hematopoietic stem cells have been investigated and applied for the treatment of certain neurological disorders for a long time. Currently, their therapeutic potential is harnessed in autologous and allogeneic hematopoietic stem cell transplantation (HSCT). Autologous HSCT is helpful in immune-mediated neurological diseases such as Multiple Sclerosis. However, clinical benefits derive more from the immunosuppressive conditioning regimen than the interaction between stem cells and the nervous system. Mainly used for hematologic malignancies, allogeneic HSCT explores the therapeutic potential of donor-derived hematopoietic stem cells. In the neurological setting, it has proven to be most valuable in Inborn Errors of Metabolism, a large spectrum of multisystem disorders characterized by congenital deficiencies in enzymes involved in metabolic pathways. Inborn Errors of Metabolism such as X-linked Adrenoleukodystrophy present with brain accumulation of enzymatic substrates that result in progressive inflammatory demyelination. Allogeneic HSCT can halt ongoing inflammatory neural destruction by replacing hematopoietic-originated microglia with donor-derived myeloid precursors. Microglia, the only neural cells successfully transplanted thus far, are the most valuable source of central nervous system metabolic correction and play a significant role in the crosstalk between the brain and hematopoietic stem cells. After transplantation, engrafted donor-derived myeloid cells modulate the neural microenvironment by recapitulating microglial functions and enhancing repair mechanisms such as remyelination. In some disorders, additional benefits result from the donor hematopoietic stem cell secretome that cross-corrects neighboring neural cells via mannose-6-phosphatase paracrine pathways. The limitations of allogeneic HSCT in this setting relate to the slow turnover of microglia and complications such as graft-vs.-host disease. These restraints have accelerated the development of hematopoietic stem cell gene therapy, where autologous hematopoietic stem cells are collected, manipulated ex vivo to overexpress the missing enzyme, and infused back into the patient. With this cellular drug vehicle strategy, the brain is populated by improved cells and exposed to supraphysiological levels of the flawed protein, resulting in metabolic correction. This review focuses on the mechanisms of brain repair resulting from HSCT and gene therapy in Inborn Errors of Metabolism. A brief mention will also be made on immune-mediated nervous system diseases that are treated with this approach.

Haematopoietic stem cell gene therapy in inborn errors of metabolism

Over the last 30 years, allogeneic haematopoietic stem cell transplantation (allo-HSCT) has been adopted as a therapeutic strategy for many inborn errors of metabolism (IEM), due to the ability of donor-derived cells to provide life-long enzyme delivery to deficient tissues and organs. However, (a) the clinical benefit of allo-HSCT is limited to a small number of IEM, (b) patients are left with a substantial residual disease burden and (c) allo-HSCT is still associated with significant short- and long-term toxicities and transplant-related mortality. Haematopoietic stem/progenitor cell gene therapy (HSPC-GT) was established in the 1990s for the treatment of selected monogenic primary immunodeficiencies and over the past few years, its use has been extended to a number of IEM. HSPC-GT is particularly attractive in neurodegenerative IEM, as gene corrected haematopoietic progenitors can deliver supra-physiological enzyme levels to difficult-to-reach areas, such as the brain and the skeleton, with potential increased clinical benefit. Moreover, HSPC-GT is associated with reduced morbidity and mortality compared to allo-HSCT, although this needs to be balanced against the potential risk of insertional mutagenesis. The number of clinical trials in the IEM field is rapidly increasing and some HSPC-GT products recently received market approval. This review describes the development of ex vivo HSPC-GT in a number of IEM, with a focus on recent results from GT clinical trials and risks versus benefits considerations, when compared to established therapeutic strategies, such as allo-HSCT.

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.

Current and Future Treatment of Mucopolysaccharidosis (MPS) Type II: Is Brain-Targeted Stem Cell Gene Therapy the Solution for This Devastating Disorder?

Mucopolysaccharidosis type II (Hunter Syndrome) is a rare, x-linked recessive, progressive, multi-system, lysosomal storage disease caused by the deficiency of iduronate-2-sulfatase (IDS), which leads to the pathological storage of glycosaminoglycans in nearly all cell types, tissues and organs. The condition is clinically heterogeneous, and most patients present with a progressive, multi-system disease in their early years. This article outlines the pathology of the disorder and current treatment strategies, including a detailed review of haematopoietic stem cell transplant outcomes for MPSII. We then discuss haematopoietic stem cell gene therapy and how this can be employed for treatment of the disorder. We consider how preclinical innovations, including novel brain-targeted techniques, can be incorporated into stem cell gene therapy approaches to mitigate the neuropathological consequences of the condition.

Pre-operative Considerations in Adult Mucopolysaccharidosis Patients Planned for Cardiac Intervention

Mucopolysaccharidoses (MPS) are rare lysosomal storage diseases characterized by multiorgan involvement and shortened longevity. Due to advances in therapies such as enzyme replacement therapy and haematopoietic stem cell therapy, life expectancy has increased posing newer challenges to patients and health professionals. One such challenge is cardiovascular manifestations of MPS, which can be life limiting and cause reduction in quality of life. Any cardiovascular intervention mandates comprehensive, multi-systemic work-up by specialist teams to optimize outcome. We highlight the importance of multidisciplinary evaluation of adult MPS patients requiring cardiovascular intervention. Clinical assessments and investigations are discussed, with a focus on the cardiac, anesthetic, airway, respiratory, radiological and psychosocial factors.

Non-cardiac Manifestations in Adult Patients With Mucopolysaccharidosis

Mucopolysaccharidoses (MPS) are a heterogeneous group of disorders that results in the absence or deficiency of lysosomal enzymes, leading to an inappropriate storage of glycosaminoglycans (GAGs) in various tissues of the body such as bones, cartilage, heart valves, arteries, upper airways, cornea, teeth, liver and nervous system. Clinical manifestations can become progressively exacerbated with age and affect their quality of life. Developments in advanced supportive treatment options such as enzyme replacement therapy (ERT), hematopoietic stem cell transplantation (HSCT) may have improved patients' life span. Adult MPS patients require specialist clinical surveillance long-term. In many cases, in addition to the MPS-related health problems, they may develop age-related complications. Considering the complexity of their clinical manifestations and lack of guidelines on the management of adult MPS disorders, multispecialty and multidisciplinary teams' care is essential to diagnose and treat health problems that are likely to be encountered. This review presents non-cardiac clinical manifestations, their pathophysiology, management and long-term outcomes in adult MPS patients.

Newborn screening of mucopolysaccharidosis type I

Mucopolysaccharidosis type I (MPS I), a lysosomal storage disease caused by a deficiency of α-L-iduronidase, leads to storage of the glycosaminoglycans, dermatan sulfate and heparan sulfate. Available therapies include enzyme replacement and hematopoietic stem cell transplantation. In the last two decades, newborn screening (NBS) has focused on early identification of the disorder, allowing early intervention and avoiding irreversible manifestations. Techniques developed and optimized for MPS I NBS include tandem mass-spectrometry, digital microfluidics, and glycosaminoglycan quantification. Several pilot studies have been conducted and screening programs have been implemented worldwide. NBS for MPS I has been established in Taiwan, the United States, Brazil, Mexico, and several European countries. All these programs measure α-L-iduronidase enzyme activity in dried blood spots, although there are differences in the analytical strategies employed. Screening algorithms based on published studies are discussed. However, some limitations remain: one is the high rate of false-positive results due to frequent pseudodeficiency alleles, which has been partially solved using post-analytical tools and second-tier tests; another involves the management of infants with late-onset forms or variants of uncertain significance. Nonetheless, the risk-benefit ratio is favorable. Furthermore, long-term follow-up of patients detected by neonatal screening will improve our knowledge of the natural history of the disease and inform better management.

Molecular characterization of a large cohort of Mucopolysaccharidosis patients: Iran Mucopolysaccharidosis RE-diagnosis Study (IMPRESsion)

Mucopolysaccharidoses (MPSs) are rare, heterogeneous inborn errors of metabolism (IEM) diagnosed through a combination of clinical, biochemical, and genetic investigations. The aim of this study was molecular characterization of the largest cohort of Iranian MPS patients (302 patients from 289 unrelated families), along with tracking their ethnicity and geographical origins. 185/289 patients were studied using an IEM-targeted NGS panel followed by complementary Sanger sequencing, which led to the diagnosis of 154 MPS patients and 5 non-MPS IEMs (diagnostic yield: 85.9%). Furthermore, 106/289 patients who were referred with positive findings went through re-analysis and confirmatory tests which confirmed MPS diagnosis in 104. Among the total of 258 MPS patients, 225 were homozygous, 90 harbored novel variants, and 9 had copy number variations. MPS IV was the most common type (34.8%) followed by MPS I (22.7%) and MPS VI (22.5%). Geographical origin analysis unveiled a pattern of distribution for frequent variants in ARSB (c.430G>A, c.962T>C [p.Leu321Pro], c.281C>A [p.Ser94*]), GALNS (c.319G>A [p.Ala107Thr], c.860C>T [p.Ser287Leu], c.1042A>G [p.Thr348Ala]), and IDUA (c.1A>C [p.Met1Leu], c.1598C>G [p.Pro533Arg], c.1562_1563insC [p.Gly522Argfs*50]). Our extensive patient cohort reveals the genetic and geographic landscape of MPS in Iran, which provides insight into genetic epidemiology of MPS and can facilitate a more cost-effective, time-efficient diagnostic approach based on the region-specific variants. This article is protected by copyright. All rights reserved.

Proposal of an Algorithm to Early Detect Attenuated Type I Mucopolysaccharidosis (MPS Ia) among Children with Growth Abnormalities

Background and Objectives: Diagnostic delay is common in attenuated Mucopolysaccharidosis Type I (MPS Ia) due to the rarity of the disease and the variability of clinical presentation. Short stature and impaired growth velocity are frequent findings in MPS Ia, but they rarely raise suspicion as paediatric endocrinologists are generally poorly trained to detect earlier and milder clinical signs of this condition. Materials and Methods: Following a consensus-based methodology, a multidisciplinary panel including paediatric endocrinologists, paediatricians with expertise in metabolic disorders, radiologists, and rheumatologists shared their experience on a possible clinical approach to the diagnosis of MPS Ia in children with short stature or stunted growth. Results: The result was the formation of an algorithm that illustrates how to raise the suspicion of MPS Ia in a patient older than 5 years with short stature and suggestive clinical signs. Conclusion: The proposed algorithm may represent a useful tool to improve the awareness of paediatric endocrinologists and reduce the diagnostic delay for patients with MPS Ia.

Case Report: Mucopolysaccharidosis Type I Treatment With α-L-Iduronidase Replacement Therapy

Mucopolysaccharidosis is a rare disease and can be divided into seven different subtypes, according to the affected enzyme. Mucopolysaccharidosis type I, the first subtype discovered and reported, mainly affects the in vivo storage of degraded sugar. The current treatment methods are symptomatic therapy, enzyme replacement therapy, and allogeneic hematopoietic stem cell transplantation. In China, the enzyme for the treatment of mucopolysaccharidosis type I was approved in June 2020. We report a case of an 18-month-old Chinese boy with mucopolysaccharidosis type I who received enzyme replacement therapy with concentrated laronidase solution. This is the second case of the disease in China, and the first case of a child under 2 years of age. Following the therapy, urine mucopolysaccharide particle levels were significantly lower, and the patient's symptoms improved. The medical records of Chinese patients who have been treated with enzyme replacement therapy for mucopolysaccharidosis type I also showed similar results. This case demonstrated that enzyme replacement therapy is a safe and effective treatment for patients with mucopolysaccharidosis type I.

Delivering gene therapy for mucopolysaccharide diseases

Mucopolysaccharide diseases are a group of paediatric inherited lysosomal storage diseases that are caused by enzyme deficiencies, leading to a build-up of glycosaminoglycans (GAGs) throughout the body. Patients have severely shortened lifespans with a wide range of symptoms including inflammation, bone and joint, cardiac, respiratory and neurological disease. Current treatment approaches for MPS disorders revolve around two main strategies. Enzyme replacement therapy (ERT) is efficacious in treating somatic symptoms but its effect is limited for neurological functions. Haematopoietic stem cell transplant (HSCT) has the potential to cross the BBB through monocyte trafficking, however delivered enzyme doses limit its use almost exclusively to MPSI Hurler. Gene therapy is an emerging therapeutic strategy for the treatment of MPS disease. In this review, we will discuss the various vectors that are being utilised for gene therapy in MPS as well as some of the most recent gene-editing approaches undergoing pre-clinical and clinical development.

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.