Clinical hints to diagnosis of attenuated forms of Mucopolysaccharidoses

Mucopolysaccharidosis Type IIIE: A Real Human Disease or a Diagnostic Pitfall?

Mucopolysaccharidoses (MPS) comprise a group of 12 metabolic disorders where defects in specific enzyme activities lead to the accumulation of glycosaminoglycans (GAGs) within lysosomes. This classification expands to 13 when considering MPS IIIE. This type of MPS, associated with pathogenic variants in the ARSG gene, has thus far been described only in the context of animal models. However, pathogenic variants in this gene also occur in humans, but are linked to a different disorder, Usher syndrome (USH) type IV, which is sparking increasing debate. This paper gathers, discusses, and summarizes arguments both for and against classifying dysfunctions of arylsulfatase G (due to pathogenic variants in the ARSG gene) in humans as another subtype of MPS, called MPS IIIE. Specific difficulties in diagnostics and the classification of some inherited metabolic diseases are also highlighted and discussed.

Lung Diseases and Rare Disorders: Is It a Lysosomal Storage Disease? Differential Diagnosis, Pathogenetic Mechanisms and Management

Pulmonologists may be involved in managing pulmonary diseases in children with complex clinical pictures without a diagnosis. Moreover, they are routinely involved in the multidisciplinary care of children with rare diseases, at baseline and during follow-up, for lung function monitoring. Lysosomal storage diseases (LSDs) are a group of genetic diseases characterised by a specific lysosomal enzyme deficiency. Despite varying pathogen and organ involvement, they are linked by the pathological accumulation of exceeding substrates, leading to cellular toxicity and subsequent organ damage. Less severe forms of LSDs can manifest during childhood or later in life, sometimes being underdiagnosed. Respiratory impairment may stem from different pathogenetic mechanisms, depending on substrate storage in bones, with skeletal deformity and restrictive pattern, in bronchi, with obstructive pattern, in lung interstitium, with altered alveolar gas exchange, and in muscles, with hypotonia. This narrative review aims to outline different pulmonary clinical findings and a diagnostic approach based on key elements for differential diagnosis in some treatable LSDs like Gaucher disease, Acid Sphingomyelinase deficiency, Pompe disease and Mucopolysaccharidosis. Alongside their respiratory clinical aspects, which might overlap, we will describe radiological findings, lung functional patterns and associated symptoms to guide pediatric pulmonologists in differential diagnosis. The second part of the paper will address follow-up and management specifics. Recent evidence suggests that new therapeutic strategies play a substantial role in preventing lung involvement in early-treated patients and enhancing lung function and radiological signs in others. Timely diagnosis, driven by clinical suspicion and diagnostic workup, can help in treating LSDs effectively.

Beyond pGALS: the need for a multifaceted musculoskeletal decision-making tool ('pGALSplus') in community-based clinical practice

Musculoskeletal (MSK) problems in children are common, and health-care professionals must identify those requiring onward referral. Paediatric gait, arms, legs and spine (pGALS) is an MSK assessment to discern abnormal joints. We aimed to identify MSK assessments to add to pGALS (pGALSplus) to facilitate decision-making in the context of exemplar conditions representing a spectrum of MSK presentations, namely JIA, mucopolysaccharidoses, muscular dystrophy and developmental co-ordination disorder. A literature review identified 35 relevant articles that focused on clinical assessments [including questionnaire(s), physical examination and functional tests] used by health-care professionals in the context of the exemplar conditions. We provide a description of these assessments and the rationale regarding how they, or components of such tools, might be useful within pGALSplus. This process provides a foundation for further work to develop and validate pGALSplus.

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.

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.

Unmet Cardiac Clinical Needs in Adult Mucopolysaccharidoses

The Mucopolysaccharidoses (MPSs) are a group of heterogenous disorders with complex multisystemic presentations. Although Haematopoietic Cell Transplantation (HCT) and Enzyme Replacement Therapy (ERT) have extended the lifespan of individuals affected with MPS well into adulthood, reversal of pre-existing cardiac, skeletal and neurocognitive deficits does not occur, so there are no truly curative treatments available to these patients at present. The medical and surgical management of cardiovascular problems in adults with MPS is complicated by these pre-existing comorbidities, requiring the involvement of multidisciplinary and multispecialty perioperative teams. This review sets out to describe the unmet cardiac needs in adults with MPS disorders including the lack of effective treatments, monitoring guidelines, and the challenges regarding expertise and training, and psychosocial support.

Misdiagnosis in mucopolysaccharidoses

Mucopolysaccharidosis (MPS) is a group of 13 hereditary metabolic diseases identified in humans (or 14 diseases if considering one MPS type described to date only in mice) in which an enzymatic defect results in the accumulation of glycosaminoglycans (GAG) in the lysosomes of cells. First of all, as a result of GAG storage, the proper functioning of the lysosome is disturbed; then, the cells, and finally, tissue, organs, and the whole organism malfunctions are observed. Due to the rarity, heterogeneity, and multi-systemic and progressive nature of MPS, they present a major diagnostic challenge. Due to the wide variation in symptoms and their similarity to other diseases, MPS is often misdiagnosed, usually as neurological diseases (like autism spectrum disorders, psychomotor hyperactivity, and intellectual disability) or rheumatology and orthopedic disorders (like juvenile idiopathic arthritis, Perthes disease, rickets, and muscular dystrophy). In this review article, we present the problems associated with the possibility of misdiagnosing MPS, discuss what diseases they can be confused with, and suggest ways to reduce these problems in the future.

Clinical and event-based outcomes of patients with mucopolysaccharidosis VI receiving enzyme replacement therapy in Turkey: a case series

Background

The objective of this study was to describe clinical manifestations and events of patients with mucopolysaccharidosis (MPS) VI in Turkey who are treated with galsulfase enzyme replacement therapy (ERT). Clinical data of 14 children with MPS VI who were followed up at the Department of Pediatrics of the Gazi University Faculty of Medicine in Ankara, Turkey were retrospectively collected from the patients’ medical records. Patients were selected based on availability of a pre-ERT baseline and follow-up clinical data for a similar period of time (1.9–3.2 years). Event data (occurrence of acute clinical events, onset of chronic events, surgeries) collected during hospital visits and telemedicine were available for up to 10 years after initiation of ERT (2.5–10 years).

Results

Age at initiation of ERT ranged from 2.8 to 15.8 years (mean age 7.5 years). All patients presented with reduced endurance and skeletal abnormalities (dysostosis multiplex) on radiography. Other common clinical manifestations were cardiac valve disease (N = 13), short stature (N = 11), cranial abnormalities on MRI (N = 10), spinal abnormalities on MRI (N = 7), and mild cognitive impairment (N = 6). School attendance was generally poor, and several patients had urinary incontinence. After 1.9 to 3.2 years of ERT, most patients showed improvements in endurance in the 6-min walk test and 3-min stair climb tests; the frequency of urinary incontinence decreased. ERT did not seem to prevent progression of cardiac valve disease, eye disorders, hearing loss, or bone disease. Long-term event-based data showed a high incidence of respiratory tract infections, adenotonsillectomy/adenoidectomy, reduced sleep quality, sleep apnea, and depression before initiation of ERT. The number of events tended to remain stable or decrease in all patients over 2.5–10 years follow-up. However, the nature of the events shifted over time, with a reduction in the frequency of respiratory tract infections and sleep problems and an increase in ophthalmologic events, ear tube insertions, and depression.

Conclusions

This case series shows the high disease burden of the MPS VI population in Turkey and provides a unique insight into their clinical journey based on real-life clinical and event-based data collected before and after initiation of ERT.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-02060-4.

Early clinical signs in lysosomal diseases

Background and aim

The lysosomal storage diseases are a group of monogenic diseases with multisystemic impairment and chronic progression induced by the deficiency of lysosomal acid hydrolases involved in the breakdown of various macromolecules. The accumulation occurs in the macrophages of the reticule-endothelial system and causes enlargement and functional impairment. The mainly involved organs are the brain, liver, spleen, bones, joints, airways, lungs, and heart. The aim of this study was to evaluate early symptoms, signs and the delay in the diagnosis of different lysosomal diseases.

Methods

The medical documentation of 188 patients with lysosomal storage disorders, aged 1-70 years, were analyzed. All these patients were specifically diagnosed, by enzyme and molecular assay.

Results

The age of clinical signs onset varies in different type of lysosomal diseases, from the first months of life or early childhood in severe form, to adulthood in attenuated forms. The delay between the clinical signs onset and specific diagnosis ranged from 0.5 months to 57.91 years.

Conclusions

The lysosomal storage diseases are rare diseases with childhood onset, but these early signs and symptoms are not recognized and are often taken into account when the vital organs damage becomes manifest.

Molecular basis of mucopolysaccharidosis IVA (Morquio A syndrome): A review and classification of GALNS gene variants and reporting of 68 novel variants

Mucopolysaccharidosis IVA (MPS IVA, Morquio A syndrome) is a rare autosomal recessive lysosomal storage disorder caused by mutations in the N‐acetylgalactosamine‐6‐sulfatase (GALNS) gene. We collected, analyzed, and uniformly summarized all published GALNS gene variants, thus updating the previous mutation review (published in 2014). In addition, new variants were communicated by seven reference laboratories in Europe, the Middle East, Latin America, Asia, and the United States. All data were analyzed to determine common alleles, geographic distribution, level of homozygosity, and genotype‐phenotype correlation. Moreover, variants were classified according to their pathogenicity as suggested by ACMG. Including those previously published, we assembled 446 unique variants, among which 68 were novel, from 1190 subjects (including newborn screening positive subjects). Variants' distribution was missense (65.0%), followed by nonsense (8.1%), splicing (7.2%), small frameshift deletions(del)/insertions(ins) (7.0%), intronic (4.0%), and large del/ins and complex rearrangements (3.8%). Half (50.4%) of the subjects were homozygous, 37.1% were compound heterozygous, and 10.7% had only one variant detected. The novel variants underwent in silico analysis to evaluate their pathogenicity. All variants were submitted to ClinVar (https://www.ncbi.nlm.nih.gov/clinvar/) to make them publicly available. Mutation updates are essential for the correct molecular diagnoses, genetic counseling, prenatal and preimplantation diagnosis, and disease management.

Approach to inherited hypertrichosis: A brief review

Hypertrichosis refers to the growth of hair, of an excessive amount and thickness, on any part of the body. It must be distinguished from hirsutism which is characterized by excess growth of hair in androgen-dependent areas on the upper lip, chin, chest, linea alba, thigh and axilla. Hypertrichosis may be localized or generalized, and congenital or acquired. Excess hair growth has a psychological impact on the child as well as the parents due to the cosmetic disfigurement it produces. Current treatment options are limited and not wholly satisfactory. Treatment should be customized according to the area, nature and amount of hair growth, age of the patient and personal preferences. In addition, when hypertrichosis occurs as a component of a syndrome, multidisciplinary management is required to address the associated systemic features. A detailed review of inherited generalized hypertrichosis is presented here with emphasis on clinical clues to identifying complex syndromes with multisystem involvement.

Glaucoma in mucopolysaccharidoses

Mucopolysaccharidoses are a group of lysosomal storage disorders that are caused by deficiency of enzymes involved in glycosaminoglycans degradation. Due to low prevalence and high childhood mortality, researches on mucopolysaccharidoses were mainly focused on the fatal manifestations. With the development of treatments, more and more mucopolysaccharidoses patients were treated by approved therapies, thereby getting prolonged life span and improved quality of life. Abnormal accumulation of glycosaminoglycans in the eye may block trabecular meshwork, thicken sclera and change mechanical behavior of lamina cribrosa, which, by increasing intraocular pressure and damaging optic nerve, could cause glaucoma. Glaucoma was the leading cause of irreversible blindness worldwide, but it was rarely reported in mucopolysaccharidoses patients. Although non-fatal, it seriously affected quality of life. Prevalence of glaucoma in mucopolysaccharidoses patients (ranged from 2.1 to 12.5%) indicated that glaucoma in patients with mucopolysaccharidoses was worthy of attention and further study, thereby improving the quality of life for MPSs patients.

Disease burden, management patterns and multidisciplinary clinical approaches for patients with MPS IVA and VI in selected Latin American Countries

Background

There is a paucity of real-world epidemiological data on patients with mucopolysaccharidoses (MPS) in Latin America. This real-world study assessed the disease burden, management patterns and multidisciplinary clinical approaches for MPS-IVA and MPS-VI patients in Latin America (Colombia, Ecuador, Mexico, Peru).

Methods

Data were collected from physicians/specialists experienced in treating MPS patients between April–June 2020, via an online patient-diary survey.

Results

Overall, 29 physicians/specialists participated in this study. Data from 98 patients were analyzed (MPS-IVA, 71 patients and MPS-VI, 27 patients). Mean age for MPS-IVA patients was 17.5 years and for MPS-VI patients was 11.6 years, and the majority were females (52% and 78%, respectively). MPS-IVA and VI patients presented a high absenteeism from school (55% and 37%, respectively; <18 years age) and workplace (78% and 100%, respectively; >18 years age), indicating an impact of the disease on some aspects of the patients' quality of life. The onset of the first symptom occurred at the age of 3.1 years for MPS-IVA patients and at 1 year for MPS-VI, with delay in diagnosis (3.5–3.9 years from symptom onset) and enzyme replacement therapy (ERT) initiation (1.1–3.6 years from diagnosis). ERT interruptions were observed for MPS-IVA (48%) and MPS-VI patients (44%), with non-availability of medication recorded as the main reason for non-adherence (46% and 60% patients, respectively). ERT showed noticeable treatment benefits in MPS-IVA/VI patients, with stabilization/reduction in complications or the number of surgeries. A multidisciplinary clinical team approach was used for patient management.

Conclusion

The disease burden for MPS-IVA/VI was high in Latin America, with consistent management, treatment and socio-demographic trends throughout the region.

Hypertrophic Cardiomyopathy in Children: Pathophysiology, Diagnosis, and Treatment of Non-sarcomeric Causes

Hypertrophic cardiomyopathy (HCM) is a myocardial disease characterized by left ventricular hypertrophy not solely explained by abnormal loading conditions. Despite its rare prevalence in pediatric age, HCM carries a relevant risk of mortality and morbidity in both infants and children. Pediatric HCM is a large heterogeneous group of disorders. Other than mutations in sarcomeric genes, which represent the most important cause of HCM in adults, childhood HCM includes a high prevalence of non-sarcomeric causes, including inherited errors of metabolism (i.e., glycogen storage diseases, lysosomal storage diseases, and fatty acid oxidation disorders), malformation syndromes, neuromuscular diseases, and mitochondrial disease, which globally represent up to 35% of children with HCM. The age of presentation and the underlying etiology significantly impact the prognosis of children with HCM. Moreover, in recent years, different targeted approaches for non-sarcomeric etiologies of HCM have emerged. Therefore, the etiological diagnosis is a fundamental step in designing specific management and therapy in these subjects. The present review aims to provide an overview of the non-sarcomeric causes of HCM in children, focusing on the pathophysiology, clinical features, diagnosis, and treatment of these rare disorders.

Estimated prevalence of mucopolysaccharidoses from population-based exomes and genomes

Background

In this study, the prevalence of different types of mucopolysaccharidoses (MPS) was estimated based on data from the exome aggregation consortium (ExAC) and the genome aggregation database (gnomAD). The population-based allele frequencies were used to identify potential disease-causing variants on each gene related to MPS I to IX (except MPS II).

Methods

We evaluated the canonical transcripts and excluded homozygous, intronic, 3′, and 5′ UTR variants. Frameshift and in-frame insertions and deletions were evaluated using the SIFT Indel tool. Splice variants were evaluated using SpliceAI and Human Splice Finder 3.0 (HSF). Loss-of-function single nucleotide variants in coding regions were classified as potentially pathogenic, while synonymous variants outside the exon–intron boundaries were deemed non-pathogenic. Missense variants were evaluated by five in silico prediction tools, and only those predicted to be damaging by at least three different algorithms were considered disease-causing.

Results

The combined frequencies of selected variants (ranged from 127 in GNS to 259 in IDUA) were used to calculate prevalence based on Hardy–Weinberg's equilibrium. The maximum estimated prevalence ranged from 0.46 per 100,000 for MPSIIID to 7.1 per 100,000 for MPS I. Overall, the estimated prevalence of all types of MPS was higher than what has been published in the literature. This difference may be due to misdiagnoses and/or underdiagnoses, especially of the attenuated forms of MPS. However, overestimation of the number of disease-causing variants by in silico predictors cannot be ruled out. Even so, the disease prevalences are similar to those reported in diagnosis-based prevalence studies.

Conclusion

We report on an approach to estimate the prevalence of different types of MPS based on publicly available population-based genomic data, which may help health systems to be better prepared to deal with these conditions and provide support to initiatives on diagnosis and management of MPS.

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

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

Novel truncating variant of PPM1D penultimate exon in a Chinese patient with Jansen-de Vries syndrome

Background

Jansen‐de Vries syndrome is a rare autosomal dominant neurodevelopmental disorder caused by pathogenic variants in the last and penultimate exons of the PPM1D gene. It is characterized by delayed psychomotor development, intellectual disability with speech delay, behavioral abnormalities, and dysmorphic features. Up to date, only 17 affected patients have been reported worldwide (no report in Chinese).

Methods

Here, we analyzed the clinical data and genetic test results of a Chinese patient with Jansen‐de Vries syndrome admitted in our hospital in May 2019.

Results

We report a 9‐month‐old boy carrying a pathogenic variant (c.1254_1255del, p.(V419Qfs*14)) in PPM1D exon 5, which can account for his phenotype. Most of his clinical features overlap with the reported phenotype, such as growth retardation, feeding difficulties, constipation, congenital abnormalities (such as atrial septal defect, ventricular septal defect, and patent ductus arteriosus), small hands and feet with broad forehead, low‐set posteriorly rotated ears, wide mouth with thin upper lip and pointed chin; however, he also presented with additional features like hepatomegaly and left inguinal hernia.

Conclusion

This is the first published case of Jansen‐de Vries syndrome in Chinese population, which will help us to enrich the clinical spectrum of this syndrome.

Mucopolysaccharidoses: early diagnostic signs in infants and children

Mucopolysaccharidoses (MPS) comprise a group of lysosomal disorders that are characterized by progressive, systemic clinical manifestations and a coarse phenotype. The different types, having clinical, biochemical, and genetic heterogeneity, share key clinical features in varying combinations, including joint and skeletal dysplasia, coarse facial features, corneal clouding, inguinal or abdominal hernias, recurrent upper respiratory tract infections, heart valve disease, carpal tunnel syndrome, and variable neurological involvement. In the severe forms, these features usually appear in the first months of life, but a correct diagnosis is often reached later when suggestive signs are manifest. All MPS types may have severe or attenuated presentations depending on the residual enzymatic activity of the patient. Based on data from the literature and from personal experience, here we underline the very early signs of the severe forms which should alert the paediatrician on their first appearance. A few early signs are typical of MPS (i.e. gibbus) while many are unspecific (hernias, upper airway infections, organomegaly, etc.), and finding the association of many unspecific signs might prompt the paediatrician to search for a common cause and to carefully look for other more specific signs (gibbus and other skeletal deformities, heart murmur). We stress the need to increase awareness of MPS among paediatricians and other specialists to shorten the still existing diagnostic delay. A timely diagnosis is mandatory for the commencement of treatment as soon as possible, when available, to possibly obtain better results.

Enzyme replacement therapy: efficacy and limitations

Enzyme replacement therapy (ERT) is available for mucopolysaccharidosis (MPS) I, MPS II, MPS VI, and MPS IVA. The efficacy of ERT has been evaluated in clinical trials and in many post-marketing studies with a long-term follow-up for MPS I, MPS II, and MPS VI. While ERT is effective in reducing urinary glycosaminoglycans (GAGs) and liver and spleen volume, cartilaginous organs such as the trachea and bronchi, bones and eyes are poorly impacted by ERT probably due to limited penetration in the specific tissue. ERT in the present formulations also does not cross the blood–brain barrier, with the consequence that the central nervous system is not cured by ERT. This is particularly important for severe forms of MPS I and MPS II characterized by cognitive decline. For severe MPS I patients (Hurler), early haematopoietic stem cell transplantation is the gold standard, while still controversial is the role of stem cell transplantation in MPS II. The use of ERT in patients with severe cognitive decline is the subject of debate; the current position of the scientific community is that ERT must be started in all patients who do not have a more effective treatment. Neonatal screening is widely suggested for treatable MPS, and many pilot studies are ongoing. The rationale is that early, possibly pre-symptomatic treatment can improve prognosis. All patients develop anti-ERT antibodies but only a few have drug-related adverse reactions. It has not yet been definitely clarified if high-titre antibodies may, at least in some cases, reduce the efficacy of ERT.

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.

The new frame for Mucopolysaccharidoses

Mucopolysaccharidoses (MPS) are genetic, progressive, lysosomal storage disorders affecting virtually all organs and systems. The first MPS were clinically identified about 100 years ago. Nowadays, the enzyme defects and related genes are known for all 11 different enzyme defects. Treatments are available for many MPS but these have only partial efficacy, especially when started late. The problems to solve are: 1) the need for an earlier diagnosis (neonatal screening? improving the awareness of physicians?); 2) prompt access to therapies; 3) improving the efficacy of the available treatments; 4) finding new treatments; and 5) the availability of specialist experts in MPS who can meet the traditional needs of MPS patients. This introduction to the IJP Supplement on MPS is a brief comment on the different papers accepted for this volume, which are in turn the elaboration of the lectures given at a meeting on the future of mucopolysaccharidoses held in Milan on 8-9 May 2017.