Incidence and natural history of mucopolysaccharidosis type III in France and comparison with United Kingdom and Greece

Evaluation of biomarkers for Sanfilippo syndrome

Sanfilippo syndrome or mucopolysaccharidosis type III (MPS III) is a childhood metabolic disorder marked by neuropathology arising due to impaired heparan sulphate (HS) catabolism. Consequently, partially degraded HS accumulates in the lysosomes of affected cells and is excreted in the urine. The measurement of HS in urine has long been considered a biomarker of Sanfilippo syndrome although it is largely non-specific. Using blood, urine and CSF collected from a cohort of Sanfilippo patients we investigated the utility of primary and secondary biomarkers to inform on disease activity. These included enzyme activity, specific oligosaccharides with non-reducing end residues reflective of the enzyme deficiency, and gangliosides. The diagnostic oligosaccharides - a HS disaccharide and tetrasaccharide - were elevated in the urine, plasma and CSF of all MPS IIIA and IIIB patients, respectively. There was no correlation between the concentrations in any of the matrices suggesting they reflect specific tissues and not overall disease burden. Enzyme activity did not inform on disease severity, with no measurable activity in CSF and activity approaching normal in MPS IIIA plasma. The concentration of gangliosides, G_M2 and G_M3, were significantly higher in the CSF of all MPS III subjects when compared to controls and correlated with the age of onset of first symptoms. Given that these gangliosides reflect delayed brain development they may be useful measures of disease burden, within the limitations of the clinical surrogates. Observation of these biochemical measurements in MPS III patients enrolled in clinical trials may determine whether they represent true pharmacodynamics biomarkers.

Analysis of the caregiver burden associated with Sanfilippo syndrome type B: panel recommendations based on qualitative and quantitative data

BACKGROUND

Sanfilippo syndrome type B (Sanfilippo B) belongs to a group of rare lysosomal storage diseases characterized by progressive cognitive decline from an early age, acute hyperactivity, and concomitant somatic symptoms. Caregivers face a unique set of challenges related to the complex nature of Sanfilippo B, but the burden and impact on quality of life (QoL) of caregivers is poorly defined and best practice guidance for clinicians is lacking.

METHODS

An international clinical advisors meeting was convened to discuss key aspects of caregiver burden associated with Sanfilippo B based on findings from qualitative and quantitative research undertaken to identify and quantify the nature and impact of the disease on patients and caregivers.

RESULTS

Providing care for patients with Sanfilippo B impinges on all aspects of family life, evolving as the patient ages and the disease progresses. Important factors contributing toward caregiver burden include sleep disturbances, impulsive and hyperactive behavior, and communication difficulties. Caregiver burden remained high throughout the life of the patient and, coupled with the physical burden of daily care, had a cumulative impact that generated significant psychological stress.

CONCLUSION

A Sanfilippo-specific QoL questionnaire is needed that is directed at caregiver needs and burden and best practice management of these domains.

Functional independence of Taiwanese patients with mucopolysaccharidoses

BACKGROUND

Information on functional strengths and weaknesses of mucopolysaccharidosis (MPS) patients is important for early intervention programs and enzyme replacement therapy (ERT).

METHODS

We used the Functional Independence Measure for Children (WeeFIM) questionnaire to assess the functional skills of 63 Taiwanese MPS patients (median age, 13 years 3 months; range, 3-20 years) from January 2012 to December 2018.

RESULTS

Mean total WeeFIM score was 75.4 of a potential score of 126. Mean total WeeFIM scores of each type (MPS I, MPS II, MPS IIIB, MPS IVA, and MPS VI) were 103.8, 76.2, 41.6, 92.2, and 113.6, respectively. Mean scores for self-care, mobility, and cognition domains were 30 (maximum 56), 23 (maximum 35), and 22 (maximum 35), respectively. MPS type IIIB patients had the lowest scores in self-care, mobility, cognition, and total domains compared to other types of MPS. All patients with ERT in MPS I, II, and IVA had higher scores in self-care and mobility domains than patients without ERT. Most patients required assistance for self-care skills, especially in grooming and bathing.

CONCLUSION

MPS patients require support and supervision in self-care tasks. For cognition tasks, MPS IIIB patients also require help. This questionnaire is useful to identify the strengths and limitations of MPS patients.

An Improved Adeno-Associated Virus Vector for Neurological Correction of the Mouse Model of Mucopolysaccharidosis IIIA

Patients with the lysosomal storage disease mucopolysaccharidosis IIIA (MPSIIIA) lack the lysosomal enzyme N-sulfoglucosamine sulfohydrolase (SGSH), one of the many enzymes involved in degradation of heparan sulfate. Build-up of un-degraded heparan sulfate results in severe progressive neurodegeneration for which there is currently no treatment. Experimental gene therapies based on gene addition are currently being explored. Following preclinical evaluation in MPSIIIA mice, an adeno-associated virus vector of serotype rh10 designed to deliver SGSH and sulfatase modifying factor 1 (SAF301) was trialed in four MPSIIIA patients, showing good tolerance and absence of adverse events with some improvements in neurocognitive measures. This study aimed to improve SAF301 further by removing sulfatase modifying factor 1 (SUMF1) and assessing if expression of this gene is needed to increase the SGSH enzyme activity (SAF301b). Second, the murine phosphoglycerate kinase (PGK) promotor was exchanged with a chicken beta actin/CMV composite (CAG) promotor (SAF302) to see if SGSH expression levels could be boosted further. The three different vectors were administered to MPSIIIA mice via intracranial injection, and SGSH expression levels were compared 4 weeks post treatment. Removal of SUMF1 resulted in marginal reductions in enzyme activity. However, promotor exchange significantly increased the amount of SGSH expressed in the brain, leading to superior therapeutic correction with SAF302. Biodistribution of SAF302 was further assessed using green fluorescent protein (GFP), indicating that vector spread was limited to the area around the injection tract. Further modification of the injection strategy to a single depth with higher injection volume increased vector distribution, leading to more widespread GFP distribution and sustained expression, suggesting this approach should be adopted in future trials.

Final results of the phase 1/2, open-label clinical study of intravenous recombinant human N-acetyl-α-d-glucosaminidase (SBC-103) in children with mucopolysaccharidosis IIIB

Mucopolysaccharidosis IIIB is caused by a marked decrease in N-acetyl-α-d-glucosaminidase (NAGLU) enzyme activity, which leads to the accumulation of heparan sulfate in key organs, progressive brain atrophy, and neurocognitive decline. In this open-label study, 11 eligible patients aged 2 to <12 years (developmental age ≥ 1 year) were sequentially allocated to recombinant human NAGLU enzyme (SBC-103) in 3 staggered- and escalating-dose groups (0.3 mg/kg [n = 3], 1.0 mg/kg [n = 4], or 3.0 mg/kg [n = 4]) by intravenous infusion every 2 weeks for 24 weeks, followed by a 4-week interruption (Part A), treatment at 1.0 and/or 3.0 mg/kg every 2 weeks starting at week 28 (Part B), and treatment at 5.0 or 10.0 mg/kg every 2 weeks (Part C) for approximately 2 total years in the study. The primary objective of the study was safety and tolerability evaluation; secondary objectives included evaluation of SBC-103 effects on total heparan sulfate levels in cerebrospinal fluid (CSF), brain structural magnetic resonance imaging (cortical gray matter volume), and neurocognitive status (age equivalent/developmental quotient). During the study, 13 treatment-emergent serious adverse events (SAEs) occurred in 3 patients; 32 infusion-associated reactions (IARs) occurred in 8 patients. Most AEs were mild and intravenous treatment with SBC-103 was well tolerated. Mean (SD) changes from baseline at 52 weeks in Part C for the 5.0 and 10.0 mg/kg doses, respectively, were: -4.7% (8.3) and - 4.7% (14.7) for heparan sulfate levels in CSF, -8.1% (3.5) and - 10.3% (9.4) for cortical gray matter volume, +2.3 (6.9) points and +1.0 (9.2) points in cognitive age equivalent and -8.9 (10.2) points and -14.4 (9.2) points in developmental quotient. In summary, SBC-103 was generally well tolerated. Changes in heparan sulfate levels in CSF were small and were not maintained from earlier study time points, there was no clear evidence overall of clinically meaningful improvement in neurocognitive function at the higher doses investigated, and no dose-dependent effects were observed.

A novel mutation of SGSH and clinical features analysis of mucopolysaccharidosis type IIIA

RATIONALE

The aim of this study was to analyze the clinical and imaging features of a pediatric patient with mucopolysaccharidosis type IIIA (MPS IIIA) and a novel mutation of the N-sulfoglucosamine sulfohydrolase (SGSH) in 1 pedigree.

PATIENT CONCERNS

An 8-year-old female patient presented with developmental regression, seizures, cerebral atrophy, thickened calvarial diploe, apathy, esotropia, slender build, thick hair, prominent eyebrows, hepatomegaly, ankle clonus, muscle and joint contractures, and funnel chest.

DIAGNOSES

The patient was diagnosed as autosomal recessive (AR) MPS IIIA with a novel mutation in the SGSH gene.

INTERVENTIONS

Genomic DNA was extracted from the peripheral blood and next-generation sequencing (NGS) technology was used to detect pathogenic genes, and the Sanger method was applied to perform pedigree verification for the detected suspicious pathogenic mutations.

OUTCOMES

The NGS done for the girl and her family showed 2 variations that were both missense mutations in SGSH. The c.1298G > A (p.Arg433Gln) was a known mutation, and the c.630 G > T (p.Trp210Cys) was a novel variation.

LESSONS

The common clinical manifestations of MPS IIIA were rapid developmental regression, seizures, cerebral atrophy, and thickened calvarial diploe. The results showed that the c.630 G > T was likely pathogenic according to bioinformatics analysis, which probably was a novel mutation. This study reports 1 case of MPS IIIA with some clinical features as determined via clinical and genetic analysis, and found a new mutation in the SGSH gene.

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.

Mucopolysaccharidosis III in Taiwan: Natural history, clinical and molecular characteristics of 28 patients diagnosed during a 21-year period

Mucopolysaccharidosis type III (MPS III, Sanfilippo syndrome) has a variable age of onset and variable rate of progression. However, information regarding the natural history of this disorder in Asian populations is limited. A retrospective analysis was carried out for 28 patients with MPS III (types IIIA [n = 3], IIIB [n = 23], and IIIC [n = 2]; 15 males and 13 females; median age, 8.2 years; age range, 2.7-26.5 years) seen in six medical centers in Taiwan from January 1996 through October 2017. The median age at confirmed diagnosis was 4.6 years. The most common initial symptom was speech delay (75%), followed by hirsutism (64%) and hyperactivity (54%). Both z scores for height and weight were negatively correlated with age (r = -.693 and -0.718, respectively; p < .01). The most prevalent clinical manifestations were speech delay (100%) and intellectual disability (100%), followed by hirsutism (93%), hyperactivity (79%), coarse facial features (68%), sleep disorders (61%), and hepatosplenomegaly (61%). Ten patients (36%) had epilepsy, and the median age at the first seizure was 11 years. Thirteen patients (46%) experienced at least one surgical procedure. At the time of the present study, 7 of the 28 patients had passed away at the median age of 13.0 years. Molecular studies showed an allelic heterogeneity without clear genotype and phenotype correlations. MPS IIIB is the most frequent subtype among MPS III in the Taiwanese population. An understanding of the natural history of MPS III may allow early diagnosis and timely management of the disease facilitating better treatment outcomes.

Trehalose reduces retinal degeneration, neuroinflammation and storage burden caused by a lysosomal hydrolase deficiency

The accumulation of undegraded molecular material leads to progressive neurodegeneration in a number of lysosomal storage disorders (LSDs) that are caused by functional deficiencies of lysosomal hydrolases. To determine whether inducing macroautophagy/autophagy via small-molecule therapy would be effective for neuropathic LSDs due to enzyme deficiency, we treated a mouse model of mucopolysaccharidosis IIIB (MPS IIIB), a storage disorder caused by deficiency of the enzyme NAGLU (alpha-N-acetylglucosaminidase [Sanfilippo disease IIIB]), with the autophagy-inducing compound trehalose. Treated naglu^{–/ –} mice lived longer, displayed less hyperactivity and anxiety, retained their vision (and retinal photoreceptors), and showed reduced inflammation in the brain and retina. Treated mice also showed improved clearance of autophagic vacuoles in neuronal and glial cells, accompanied by activation of the TFEB transcriptional network that controls lysosomal biogenesis and autophagic flux. Therefore, small-molecule-induced autophagy enhancement can improve the neurological symptoms associated with a lysosomal enzyme deficiency and could provide a viable therapeutic approach to neuropathic LSDs.

Abbreviations: ANOVA: analysis of variance; Atg7: autophagy related 7; AV: autophagic vacuoles; CD68: cd68 antigen; ERG: electroretinogram; ERT: enzyme replacement therapy; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GFAP: glial fibrillary acidic protein; GNAT2: guanine nucleotide binding protein, alpha transducing 2; HSCT: hematopoietic stem cell transplantation; INL: inner nuclear layer; LC3: microtubule-associated protein 1 light chain 3 alpha; MPS: mucopolysaccharidoses; NAGLU: alpha-N-acetylglucosaminidase (Sanfilippo disease IIIB); ONL: outer nuclear layer; PBS: phosphate-buffered saline; PRKCA/PKCα: protein kinase C, alpha; S1BF: somatosensory cortex; SQSTM1: sequestosome 1; TEM: transmission electron microscopy; TFEB: transcription factor EB; VMP/VPL: ventral posterior nuclei of the thalamus

Utilizing ExAC to assess the hidden contribution of variants of unknown significance to Sanfilippo Type B incidence

Given the large and expanding quantity of publicly available sequencing data, it should be possible to extract incidence information for monogenic diseases from allele frequencies, provided one knows which mutations are causal. We tested this idea on a rare, monogenic, lysosomal storage disorder, Sanfilippo Type B (Mucopolysaccharidosis type IIIB). Sanfilippo Type B is caused by mutations in the gene encoding α-N-acetylglucosaminidase (NAGLU). There were 189 NAGLU missense variants found in the ExAC dataset that comprises roughly 60,000 individual exomes. Only 24 of the 189 missense variants were known to be pathogenic; the remaining 165 variants were of unknown significance (VUS), and their potential contribution to disease is unknown. To address this problem, we measured enzymatic activities of 164 NAGLU missense VUS in the ExAC dataset and developed a statistical framework for estimating disease incidence with associated confidence intervals. We found that 25% of VUS decreased the activity of NAGLU to levels consistent with Sanfilippo Type B pathogenic alleles. We found that a substantial fraction of Sanfilippo Type B incidence (67%) could be accounted for by novel mutations not previously identified in patients, illustrating the utility of combining functional activity data for VUS with population-wide allele frequency data in estimating disease incidence.

Lysosomal N-acetyltransferase interacts with ALIX and is detected in extracellular vesicles

Heparan acetyl CoA: α-glucosaminide N-acetyltransferase (HGSNAT) is a lysosomal multi-pass transmembrane protein whose deficiency may lead to an accumulation of heparan sulphate and the neurodegenerative lysosomal storage disorder mucopolysaccharidosis (MPS) IIIC. In this study, HGSNAT activity was detected in extracellular vesicles isolated from both human urine and culture medium conditioned with HEK 293T cells. We also demonstrate that HGSNAT co-immunoprecipitates with antibodies to ALIX, which is associated with the endosomal sorting complexes required for transport (ESCRT) proteins, and is implicated in the targeting of proteins to intraluminal vesicles of multivesicular bodies, the origin of exosomes. Furthermore, mutation of a putative LYPXnL-based binding site within HGSNAT for the V-domain of ALIX ablated association of HGSNAT with ALIX, post-translational maturation, and transport through the endo-lysosomal network. Unexpectedly, however, a mutation within the V-domain of ALIX demonstrated enhanced HGSNAT association, perhaps due to the actual involvement of other binding sites in this interaction. Indeed, HGSNAT still co-immunoprecipitates with truncations of ALIX lacking the V-domain. Interestingly, CRISPR/Cas9 mediated knock-down of ALIX did not inhibit HGSNAT trafficking through the endo-lysosomal network, suggesting that there is an alternative pathway for trafficking HGSNAT that does not require ALIX. Nonetheless, the targeting of HGSNAT to extracellular vesicles may provide a mechanism to subsequently transfer this enzyme extracellularly to provide a foundation for a therapy for MPS IIIC patients.

MPS-IIIA mice acquire autistic behaviours with age

Mucopolysaccharidosis (MPS) type IIIA is an inherited, neurodegenerative lysosomal storage disorder resulting from mutations in the SGSH gene. Consequently, N-sulphoglucosamine sulphohydrolase enzyme activity is reduced resulting in impaired catabolism of heparan sulphate. After an asymptomatic period, patients typically show a progressive loss of cognitive and motor skills, with death often during the second decade of life. The diagnostic criteria of autism spectrum disorders (ASD) include impaired communication and social interactions, as well as displays of repetitive behaviours and fixed interests. Children with MPS-IIIA have been shown to exhibit decreased social communicative behaviours from approximately 3-4 years of age but behavioural stereotypies are mostly absent. In this study, we investigated whether a mouse model of MPS-IIIA exhibited ASD-like symptoms. The BTBR T⁺Itpr3^tf/J inbred mouse model of autism was used as a positive control. Male MPS-IIIA and BTBR mice were less sociable compared with unaffected C57BL/6 male mice in the reciprocal social approach test administered at 20 weeks of age. Alternations in the frequency of social interactions was not evident at earlier stages of the disease course, suggesting an acquisition of ASD-like social behaviours. Stereotypical behaviours were not evident in male MPS-IIIA mice in the marble-burying test nor was the quality of nest constructed by mice affected. Collectively, these data suggest that MPS-IIIA mice acquire autistic social behaviours similar to the human condition, and thus they may be useful for elucidating symptom generating mechanisms and novel treatments for ASD.

Observational Prospective Natural History of Patients with Sanfilippo Syndrome Type B

OBJECTIVE

To evaluate the natural course of disease progression in patients with Sanfilippo syndrome type B (mucopolysaccharidosis type IIIB), identify potential end points for future therapy trials, and characterize biomarkers related to the disease.

STUDY DESIGN

A prospective, multicenter study was conducted. Baseline, 6-month, and 12-month assessments included neurodevelopmental status (Bayley Scales of Infant Development, Third edition), adaptive status (Vineland Adaptive Behavior Scales, Second Edition), volumetric brain magnetic resonance imaging, cerebrospinal fluid heparan sulfate, and urine glycosaminoglycan (GAG) measurements.

RESULTS

Nineteen patients aged 1.6-31.7 years were enrolled. Over 12 months, cognition, adaptive behavior, and cortical gray matter volume (GMV) declined in most patients. For patients diagnosed at <6 years, although there was no overall mean change over 12 months, there were 10%-48%, 3%-66%, and 1%-14% decreases in cognitive development quotient score, Vineland Adaptive Behavior Scales, Second Edition development quotient score, and cortical GMV in 8/12, 9/11, and 10/11 patients, respectively. Mean urine GAG and cerebrospinal fluid heparan sulfate levels were stable, but patients diagnosed at <6 years (n = 14) had higher levels than those ≥6 years at diagnosis (n = 4), which was likely associated with age as they also were generally younger.

CONCLUSIONS

Cognition, adaptive behavior, and cortical GMV measures sensitively tracked deterioration in patients with mucopolysaccharidosis type IIIB aged ≤8.6 years. Biomarkers may have prognostic value, but their sensitivity to disease progression requires further investigation. These findings should help evaluate enzyme replacement and gene therapy agents for this rare, devastating, neurodegenerative disease.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT01509768.

Epidemiology of Sanfilippo syndrome: results of a systematic literature review

Background

Sanfilippo syndrome (mucopolysaccharidosis [MPS] III subtypes A, B, C, and D) is a rare autosomal recessive inherited metabolic disorder that causes progressive neurocognitive degeneration. This systematic literature review was undertaken to compile and assess published epidemiological data, including various frequency measures and geographical variation on Sanfilippo syndrome.

Methods

The following databases were systematically searched for terms related to Sanfilippo syndrome epidemiology: Medline, Embase, Cochrane Database of Systematic Reviews, Academic Search Complete, Cumulative Index to Nursing and Allied Health Literature, and the Centre for Reviews and Dissemination. Qualitative synthesis of research findings was performed.

Results

Of 2794 publications found in the initial search, 116 were deemed eligible after title and abstract screening. Following full-text review, 46 papers were included in the qualitative synthesis. Results of this systematic literature review indicate that lifetime risk at birth ranges from 0.17–2.35 per 100,000 live births for all 4 subtypes of MPS III together, and from 0.00–1.62 per 100,000 live births for the most frequent subtype, MPS IIIA.

Conclusion

All 4 subtypes of MPS III are exceptionally rare, but they each have devastating effects on children. Higher-quality epidemiological data are needed to appropriately target resources for disease research and management.

Electronic supplementary material

The online version of this article (10.1186/s13023-018-0796-4) contains supplementary material, which is available to authorized users.

Failure to shorten the diagnostic delay in two ultra-orphan diseases (mucopolysaccharidosis types I and III): potential causes and implications

Background

Rare diseases are often un- or misdiagnosed for extended periods, resulting in a long diagnostic delay that may significantly add to the burden of the disease. An early diagnosis is particularly essential if a disease-modifying treatment is available. The purpose of this study was to assess the extent of the diagnostic delay in the two ultra-rare diseases, i.e., mucopolysaccharidosis I (MPS I) and III (MPS III), both of which are lysosomal storage disorders with different phenotypic severities (MPS 1 is characterized by the severe Hurler and the more attenuated non-Hurler phenotypes, MPS III is characterized by the severe rapidly progressing (RP) phenotype and more attenuated slowly progressing (SP) phenotype). We investigated whether the diagnostic delay changed over the previous decades.

Results

The diagnostic delay, which is defined as the time between the first visit to a medical doctor for disease-related symptoms and the final diagnosis, was assessed using telephone interviews with patients diagnosed between 1988 and 2017 and/or their parents or legal guardian(s). In addition, the medical charts were reviewed. For MPS I (n = 29), the median diagnostic delay was 8 months (range 1-24 months) for Hurler patients and 28 months (range 2-147 months) for non-Hurler patients. For MPS III (n = 46), the median diagnostic delay was 33 months (range 1-365 months). No difference was observed between the RP and SP phenotypic groups. Comparing the diagnostic delay over time using 5-year time intervals, no reduction in the diagnostic delay was observed for MPS I or MPS III.

Conclusions

In the Netherlands, the time to diagnosis for patients with MPS I and MPS III has not changed between 1988 and 2017, and an extensive delay still exists between the first visit to a medical doctor for disease-related symptoms and the final diagnosis. The numerous campaigns launched to increase awareness, leading to earlier diagnosis of these rare disorders, particularly of MPS I, have failed to achieve their goal. Robust selected screening protocols embedded in national guidelines and newborn screening for disorders that meet the criteria for population screening may be the only effective approaches for reducing the diagnostic delay.

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

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

Assessments of neurocognitive and behavioral function in the mucopolysaccharidoses

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

Epilepsy in mucopolysaccharidosis disorders

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

Symptoms of Autism Spectrum Disorder (ASD) in Individuals with Mucopolysaccharide Disease Type III (Sanfilippo Syndrome): A Systematic Review

The prevalence of autism spectrum disorder (ASD) in many genetic disorders is well documented but not as yet in Mucopolysaccharidosis type III (MPS III). MPS III is a recessively inherited metabolic disorder and evidence suggests that symptoms of ASD present in MPS III. This systematic review examined the extant literature on the symptoms of ASD in MPS III and quality assessed a total of 16 studies. Results indicated that difficulties within speech, language and communication consistent with ASD were present in MPS III, whilst repetitive and restricted behaviours and interests were less widely reported. The presence of ASD-like symptoms can result in late diagnosis or misdiagnosis of MPS III and prevent opportunities for genetic counselling and the provision of treatments.

Prediction of phenotypic severity in mucopolysaccharidosis type IIIA

Objective

Mucopolysaccharidosis IIIA or Sanfilippo disease type A is a progressive neurodegenerative disorder presenting in early childhood, caused by an inherited deficiency of the lysosomal hydrolase sulfamidase. New missense mutations, for which genotype–phenotype correlations are currently unknown, are frequently reported, hampering early prediction of phenotypic severity and efficacy assessment of new disease‐modifying treatments. We aimed to design a method to determine phenotypic severity early in the disease course.

Methods

Fifty‐three patients were included for whom skin fibroblasts and data on disease course and mutation analysis were available. Patients were phenotypically characterized on clinical data as rapidly progressing or slowly progressing. Sulfamidase activity was measured in fibroblasts cultured at 37 °C and at 30 °C.

Results

Sulfamidase activity in fibroblasts from patients homozygous or compound heterozygous for a combination of known severe mutations remained below the limit of quantification under both culture conditions. In contrast, sulfamidase activity in fibroblasts from patients homozygous or compound heterozygous for a known mild mutation increased above the limit of quantification when cultured at 30 °C. With division on the basis of the patients' phenotype, fibroblasts from slowly progressing patients could be separated from rapidly progressing patients by increase in sulfamidase activity when cultured at 30 °C (p < 0.001, sensitivity = 96%, specificity = 93%).

Interpretation

Phenotypic severity strongly correlates with the potential to increase sulfamidase activity in fibroblasts cultured at 30 °C, allowing reliable distinction between patients with rapidly progressing or slowly progressing phenotypes. This method may provide an essential tool for assessment of treatment effects and for health care and life planning decisions. Ann Neurol 2017;82:686–696

Mortality in patients with Sanfilippo syndrome

BACKGROUND

Sanfilippo syndrome (mucopolysaccharidosis type III; MPS III) is an inherited monogenic lysosomal storage disorder divided into subtypes A, B, C and D. Each subtype is characterized by deficiency of a different enzyme participating in metabolism of heparan sulphate. The resultant accumulation of this substrate in bodily tissues causes various malfunctions of organs, ultimately leading to premature death. Eighty-four, 24 and 5 death certificates of patients with Sanfilippo syndrome types A, B and C, respectively, were obtained from the Society of Mucopolysaccharide Diseases (UK) to better understand the natural course of these conditions, covering the years 1977-2007.

RESULTS

In Sanfilippo syndrome type A mean age at death (± standard deviation) was 15.22 ± 4.22 years, 18.91 ± 7.33 years for patients with Sanfilippo syndrome type B and 23.43 ± 9.47 years in Sanfilippo syndrome type C. Patients with Sanfilippo syndrome type A showed significant increase in longevity over the period of observation (p = 0.012). Survival rates of patients with Sanfilippo syndrome type B did not show a statistically significant improvement (p = 0.134). In Sanfilippo syndrome types A and B, pneumonia was identified as the leading cause of death.

CONCLUSIONS

The analysis of 113 death certificates of patients with Sanfilippo syndrome in the UK has demonstrated that the longevity has improved significantly in patients with Sanfilippo syndrome type A over a last few decades. The numbers of patients with Sanfilippo syndrome types B and C were too small to identify any significant trend changes for these groups. Respiratory tract infections, notably pneumonia, remain the leading cause of mortality in Sanfilippo syndrome types A and B. The extended lifespans of patients with Sanfilippo syndrome type A were achieved despite the lack of therapies to target the primary insult or pathophysiology of the disease. However, the mean age at death of these patients remains low when compared with the general population. Therefore, there is an urgent need for effective disease-specific therapies to be developed so that the quality of life and survival of patients with Sanfilippo syndrome can be improved.

Clinical, biochemical and molecular features of Iranian families with mucopolysaccharidosis: A case series

This study aims to ascertain the genetic variants which contribute to the most common types of MPS in eleven Iranian families. Clinical and biochemical features were obtained during initial examination and patients were further investigated for genetic defects in the MPS genes. Peripheral blood samples were obtained from all family members after obtaining written informed consent. Based on the patient's clinical diagnosis, three different genetic tests including Sanger sequencing of four genes (IDUA, IDS, SGSH, and GALNS), targeted panel (10 genes) and Whole Exome Sequencing (WES) techniques were applied to identify the causative variants. A total of 12 different mutations were identified in five genes, including nine novel mutations and three previously reported missense mutations. Sanger sequencing confirmation of the identified mutations determined one case of compound heterozygous in the NAGLU gene. In this study, novel mutations in MPS related genes were identified attempting to characterize the type and subtype of the disease using molecular approaches. Results of the study positively contribute to mutation spectrum of IDUA, IDS, SGSH, NAGLU, and GALNS genes in the Iranian cohort. It may also enrich genetic counseling for rapid risk assessment and disease management.

Update of the spectrum of mucopolysaccharidoses type III in Tunisia: identification of three novel mutations and in silico structural analysis of the missense mutations

BACKGROUND

Mucopolysaccharidoses type III (MPS III) are a group of autosomal recessive lysosomal storage diseases, caused by mutations in genes that code for enzymes involved in the lysosomal degradation of heparan sulphate: heparan sulfate sulfamidase (SGSH), α-Nacetylglucosaminidase (NAGLU), heparan sulfate acetyl-CoA: α-glucosaminide N-acetyltransferase (HGSNAT), and N-acetylglucosamine-6-sulfatase (GNS).

METHODS

In this study, we have performed the molecular analysis of the SGSH, NAGLU and HGSNAT genes in 10 patients from 6 different MPS III Tunisian families.

RESULTS

In the SGSH gene, two mutations were identified: one novel (p.D477N) and one already described (p.Q365X). In the NAGLU gene, two novel mutations were discovered (p.L550P and p.E153X). For the novel missense mutations found in these two genes we performed an in silico structural analysis and the results were consistent with the clinical course of the patients harboring those mutations. Finally, in HGSNAT gene, we found the splicesite mutation c.234+1G>A that had already been reported as relatively frequent in MPS IIIC patients from countries surrounding the basin of the Mediterranean sea. Its presence in two Tunisian MPS IIIC families points to the hypothesis of its peri Mediterranean origin. With the exception of the c.234+1G>A mutation, that was identified in two unrelated MPS IIIC families, the other identified mutations were family-specific and were always found in homozygosity in the patients studied, thus reflecting the existence of consanguinity in MPS III Tunisian families.

CONCLUSIONS

Three novel mutations are reported here, further contributing to the knowledge of the molecular basis of these diseases. The results of this study will allow carrier detection in affected families and prenatal molecular diagnosis, leading to an improvement in genetic counseling.

Intracerebral gene therapy in children with mucopolysaccharidosis type IIIB syndrome: an uncontrolled phase 1/2 clinical trial

BACKGROUND

Mucopolysaccharidosis type IIIB syndrome (also known as Sanfilippo type B syndrome) is a lysosomal storage disease resulting in progressive deterioration of cognitive acquisition after age 2-4 years. No treatment is available for the neurological manifestations of the disease. We sought to assess the safety and efficacy of a novel intracerebral gene therapy.

METHODS

Local regulatory authorities in France allowed inclusion of up to four children in this phase 1/2 study. Treatment was 16 intraparenchymal deposits (four in the cerebellum) of a recombinant adenoassociated viral vector serotype 2/5 (rAAV2/5) encoding human α-N-acetylglucosaminidase (NAGLU) plus immunosuppressive therapy. We assessed tolerance, neurocognitive progression, brain growth, NAGLU enzymatic activity in CSF, and specific anti-NAGLU immune response for 30 months after surgery. This trial is registered with EudraCT, number 2012-000856-33, and the International Standard Clinical Trial Registry, number ISRCTN19853672.

FINDINGS

Of seven eligible children, the four youngest, from France (n=2), Italy (n=1), and Greece (n=1), aged 20, 26, 30, and 53 months, were included between February, 2012, and February, 2014. 125 adverse events were recorded, of which 117 were treatment emergent and included six classified as severe, but no suspected unexpected serious adverse drug reactions were seen. Vector genomes were detected in blood for 2 days after surgery. Compared with the natural history of mucopolysaccharidosis type III syndromes, neurocognitive progression was improved in all patients, with the youngest patient having function close to that in healthy children. Decrease in developmental quotient was -11·0 points in patient one, -23·0 in patient two, -29·0 in patient three, and -17·0 in patient four, compared with -37·7 in the natural history of the disease. NAGLU activity was detected in lumbar CSF and was 15-20% of that in unaffected children. Circulating T lymphocytes that proliferated and produced tumour necrosis factor α upon ex-vivo exposure to NAGLU antigens were detectable at 1-12 months and 3-12 months, respectively, but not at 30 months in three of four patients.

INTERPRETATION

Intracerebral rAVV2/5 was well tolerated and induced sustained enzyme production in the brain. The initial specific anti-NAGLU immune response that later subsided suggested acquired immunological tolerance. The best results being obtained in the youngest patient implies a potential window of opportunity. Longer follow-up is needed to further assess safety outcomes and persistence of improved cognitive development.

FUNDING

Association Française Contre les Myopathies, Vaincre les Maladies Lysosomales, Institut Pasteur, and UniQure.

Epidemiology of mucopolysaccharidoses

The aim of this study was to obtain data about the epidemiology of the different types of mucopolysaccharidoses in Japan and Switzerland and to compare with similar data from other countries. Data for Japan was collected between 1982 and 2009, and 467 cases with MPS were identified. The combined birth prevalence was 1.53 per 100,000 live births. The highest birth prevalence was 0.84 for MPS II, accounting for 55% of all MPS. MPS I, III, and IV accounted for 15, 16, and 10%, respectively. MPS VI and VII were more rare and accounted for 1.7 and 1.3%, respectively. A retrospective epidemiological data collection was performed in Switzerland between 1975 and 2008 (34years), and 41 living MPS patients were identified. The combined birth prevalence was 1.56 per 100,000 live births. The highest birth prevalence was 0.46 for MPS II, accounting for 29% of all MPS. MPS I, III, and IV accounted for 12, 24, and 24%, respectively. As seen in the Japanese population, MPS VI and VII were more rare and accounted for 7.3 and 2.4%, respectively. The high birth prevalence of MPS II in Japan was comparable to that seen in other East Asian countries where this MPS accounted for approximately 50% of all forms of MPS. Birth prevalence was also similar in some European countries (Germany, Northern Ireland, Portugal and the Netherlands) although the prevalence of other forms of MPS is also reported to be higher in these countries. Birth prevalence of MPS II in Switzerland and other European countries is comparatively lower. The birth prevalence of MPS III and IV in Switzerland is higher than in Japan but comparable to that in most other European countries. Moreover, the birth prevalence of MPS VI and VII was very low in both, Switzerland and Japan. Overall, the frequency of MPS varies for each population due to differences in ethnic backgrounds and/or founder effects that affect the birth prevalence of each type of MPS, as seen for other rare genetic diseases. Methods for identification of MPS patients are not uniform across all countries, and consequently, if patients are not identified, recorded prevalence rates will be aberrantly low.

Recommendations on clinical trial design for treatment of Mucopolysaccharidosis Type III

Background

Mucopolysaccharidosis type III is a progressive, neurodegenerative lysosomal storage disorder for which there is currently no effective therapy. Though numerous potential therapies are in development, there are several challenges to conducting clinical research in this area. We seek to make recommendations on the approach to clinical research in MPS III, including the selection of outcome measures and trial endpoints, in order to improve the quality and impact of research in this area.

Results

An international workshop involving academic researchers, clinical experts and industry groups was held in June 2015, with presentations and discussions on disease pathophysiology, biomarkers, potential therapies and clinical outcome measures. A set of recommendations was subsequently prepared by a working group and reviewed by all delegates. We present a series of 11 recommendations regarding the conduct of clinical research, outcome measures and management of natural history data in Mucopolysaccharidosis type III.

Conclusions

Improving the quality of clinical research in Mucopolysaccharidosis type III will require an open, collaborative and systematic approach between academic researchers, clinicians and industry. Natural history data should be published as soon as possible and ideally collated in a central repository. There should be agreement on outcome measures and instruments for evaluation of clinical outcomes to maximise the effectiveness of current and future clinical research.

Natural History of Sanfilippo Syndrome Type C in Boyacá, Colombia

Mucopolysaccharidosis type III, or Sanfilippo syndrome, is an autosomal recessive disorder characterized by impairment in the degradation of Heparan sulfate. Here the authors describe the natural history of 5 related individuals; all associated through a large pedigree which reports a total of 11 affected members, originally from the Boyacá region in Colombia, diagnosed with MPS IIIC who all harbor a novel mutation in HGSNAT. The authors report an unusually high incidence of the disease in this population. The clinical features are similar to previously described patients, although some differences in the degree of severity and end-stage of the disease are seen in this specific group. The authors consider that the high degree of endogamy in this specific population could underlie modifying factors for the severity of presentation in these patients. Future studies might provide more information on the functional effect of this novel mutation, which could define this group as a genetic isolate.

Long-term clinical course of a patient with mucopolysaccharidosis type IIIB

Mucopolysaccharidosis type III (MPS III) is a rare genetic disorder caused by lysosomal storage of heparan sulfate. MPS IIIB results from a deficiency in the enzyme alpha-N-acetyl-D-glucosaminidase (NAGLU). Affected patients begin showing behavioral changes, progressive profound mental retardation, and severe disability from the age of 2 to 6 years. We report a patient with MPS IIIB with a long-term follow-up duration. He showed normal development until 3 years. Subsequently, he presented behavioral changes, sleep disturbance, and progressive motor dysfunction. He had been hospitalized owing to recurrent pneumonia and epilepsy with severe cognitive dysfunction. The patient had compound heterozygous c.1444C>T (p.R482W) and c.1675G>T (p.D559Y) variants of NAGLU. Considering that individuals with MPS IIIB have less prominent facial features and skeletal changes, evaluation of long-term clinical course is important for diagnosis. Although no effective therapies for MPS IIIB have been developed yet, early and accurate diagnosis can provide important information for family planning in families at risk of the disorder.

Carbohydrate-Processing Enzymes of the Lysosome: Diseases Caused by Misfolded Mutants and Sugar Mimetics as Correcting Pharmacological Chaperones

Lysosomal storage diseases are hereditary disorders caused by mutations on genes encoding for one of the more than fifty lysosomal enzymes involved in the highly ordered degradation cascades of glycans, glycoconjugates, and other complex biomolecules in the lysosome. Several of these metabolic disorders are associated with the absence or the lack of activity of carbohydrate-processing enzymes in this cell compartment. In a recently introduced therapy concept, for susceptible mutants, small substrate-related molecules (so-called pharmacological chaperones), such as reversible inhibitors of these enzymes, may serve as templates for the correct folding and transport of the respective protein mutant, thus improving its concentration and, consequently, its enzymatic activity in the lysosome. Carbohydrate-processing enzymes in the lysosome, related lysosomal diseases, and the scope and limitations of reported reversible inhibitors as pharmacological chaperones are discussed with a view to possibly extending and improving research efforts in this area of orphan diseases.

Unique medical issues in adult patients with mucopolysaccharidoses

The mucopolysaccharidoses are a group of inherited metabolic diseases caused by deficiencies in enzymes involved in the sequential degradation of glycosaminoglycans (GAGs) leading to substrate accumulation in various tissues and organs. GAG accumulation can cause growth retardation and progressive damage to respiratory, cardiovascular, musculoskeletal, nervous, gastrointestinal, auditory, and visual systems. In the past, few people with severe phenotypic mucopolysaccharidosis (MPS) reached adulthood. However, better methods for diagnosis, multi-disciplinary care, and new therapies have extended lifespan, leading to an increasing number of patients surviving beyond childhood. The growing number of adult MPS patients poses significant challenges for clinicians who may not be familiar with the clinical manifestations of MPS. In addition, as new interventions have changed the natural history of these disorders, it is difficult to anticipate both the impact on life expectancy and other complications that may occur as these patients age. Because the MPS disorders are multi-organ diseases, their management requires a coordinated multi-disciplinary approach. Here we discuss the unique pattern of medical issues and multi-organ involvement in adult patients with MPS and identify the challenges that are associated with management of MPS. This review is based on information from an expert investigator meeting with MPS specialists held October 2-4, 2014 in Dublin, Ireland, as well as on current literature searches focusing on MPS and adults.

External genitalia hypertrophy in an adolescent girl with Sanfilippo syndrome

OBJECTIVE

To report unusual gynaecological features associated with Sanfilippo syndrome, a rare progressive multisystem storage disorder.

CASE

A 10-year-old adolescent girl with Sanfilippo syndrome type B, presented to the Center for Adolescent Medicine accompanied by her mother. Maternal anxiety was related to a palpable mass over the adolescent's external genitalia that had been causing her discomfort and exacerbation of her behavioural problems when wearing trousers. The mass was also a site of blood accumulation during her menstruation causing hygiene issues. Gynaecological examination revealed hypertrophy and thickening of the adolescent's hymen, labia minora and the posterior fourchette, that protruded like a mass in her perineum. These findings were attributed to the accumulation of heparan sulphate in the connective tissue of her external genitalia and perineal area. Reassurance as well as counselling about hygiene and avoidance of tight clothes were provided to the mother.

CONCLUSION

Girls with mucopolysaccharidoses need monitoring for evolving gynaecological problems in order to improve their quality of life.

Progressive neurologic and somatic disease in a novel mouse model of human mucopolysaccharidosis type IIIC

Mucopolysaccharidosis type IIIC (MPSIIIC) is a severe lysosomal storage disease caused by deficiency in activity of the transmembrane enzyme heparan-α-glucosaminide N-acetyltransferase (HGSNAT) that catalyses the N-acetylation of α-glucosamine residues of heparan sulfate. Enzyme deficiency causes abnormal substrate accumulation in lysosomes, leading to progressive and severe neurodegeneration, somatic pathology and early death. There is no cure for MPSIIIC, and development of new therapies is challenging because of the unfeasibility of cross-correction. In this study, we generated a new mouse model of MPSIIIC by targeted disruption of the Hgsnat gene. Successful targeting left LacZ expression under control of the Hgsnat promoter, allowing investigation into sites of endogenous expression, which was particularly prominent in the CNS, but was also detectable in peripheral organs. Signs of CNS storage pathology, including glycosaminoglycan accumulation, lysosomal distension, lysosomal dysfunction and neuroinflammation were detected in 2-month-old animals and progressed with age. Glycosaminoglycan accumulation and ultrastructural changes were also observed in most somatic organs, but lysosomal pathology seemed most severe in liver. Furthermore, HGSNAT-deficient mice had altered locomotor and exploratory activity and shortened lifespan. Hence, this animal model recapitulates human MPSIIIC and provides a useful tool for the study of disease physiopathology and the development of new therapeutic approaches.

Genes with high penetrance for syndromic and non-syndromic autism typically function within the nucleus and regulate gene expression

BACKGROUND

Intellectual disability (ID), autism, and epilepsy share frequent yet variable comorbidities with one another. In order to better understand potential genetic divergence underlying this variable risk, we studied genes responsible for monogenic IDs, grouped according to their autism and epilepsy comorbidities.

METHODS

Utilizing 465 different forms of ID with known molecular origins, we accessed available genetic databases in conjunction with gene ontology (GO) to determine whether the genetics underlying ID diverge according to its comorbidities with autism and epilepsy and if genes highly penetrant for autism or epilepsy share distinctive features that set them apart from genes that confer comparatively variable or no apparent risk.

RESULTS

The genetics of ID with autism are relatively enriched in terms associated with nervous system-specific processes and structural morphogenesis. In contrast, we find that ID with highly comorbid epilepsy (HCE) is modestly associated with lipid metabolic processes while ID without autism or epilepsy comorbidity (ID only) is enriched at the Golgi membrane. Highly comorbid autism (HCA) genes, on the other hand, are strongly enriched within the nucleus, are typically involved in regulation of gene expression, and, along with IDs with more variable autism, share strong ties with a core protein-protein interaction (PPI) network integral to basic patterning of the CNS.

CONCLUSIONS

According to GO terminology, autism-related gene products are integral to neural development. While it is difficult to draw firm conclusions regarding IDs unassociated with autism, it is clear that the majority of HCA genes are tightly linked with general dysregulation of gene expression, suggesting that disturbances to the chronology of neural maturation and patterning may be key in conferring susceptibility to autism spectrum conditions.

Insulin Receptor Antibody-α-N-Acetylglucosaminidase Fusion Protein Penetrates the Primate Blood-Brain Barrier and Reduces Glycosoaminoglycans in Sanfilippo Type B Fibroblasts

Mucopolysaccharidosis Type IIIB (MPSIIIB) is caused by mutations in the gene encoding the lysosomal enzyme, α-N-acetylglucosaminidase (NAGLU). MPSIIIB presents with severe disease of the central nervous system, but intravenous NAGLU enzyme replacement therapy has not been developed because the NAGLU enzyme does not cross the blood-brain barrier (BBB). A BBB-penetrating form of the enzyme was produced by re-engineering NAGLU as an IgG-enzyme fusion protein, where the IgG domain is a monoclonal antibody (mAb) against the human insulin receptor (HIR). The HIRMAb traverses the BBB via transport on the endogenous insulin receptor and acts as a molecular Trojan horse to ferry the fused NAGLU across the BBB from blood. The NAGLU was fused to the carboxyl terminus of each heavy chain of the HIRMAb via an extended 31-amino acid linker, and the fusion protein is designated HIRMAb-LL-NAGLU. The fusion protein retains high affinity binding to the HIR, and on a molar basis has an enzyme activity equal to that of recombinant human NAGLU. Treatment of MPSIIIB fibroblasts with the fusion protein normalizes intracellular NAGLU enzyme activity and reduces sulfate incorporation into intracellular glycosoaminoglycan. The fusion protein is targeted to the lysosomal compartment of the cells as shown by confocal microscopy. The fusion protein was radiolabeled with the [(125)I]-Bolton-Hunter reagent and injected intravenously in the adult Rhesus monkey. The fusion protein was rapidly cleared from plasma by all major peripheral organs. The high brain uptake of the fusion protein, 1% injected dose/brain, enables normalization of brain NAGLU enzyme activity with a therapeutic dose of 1 mg/kg. The HIRMAb-LL-NAGLU fusion protein is a new treatment of the brain in MPSIIIB, which can be administered by noninvasive intravenous infusion.

A Prospective Natural History Study of Mucopolysaccharidosis Type IIIA

OBJECTIVES

To characterize the clinical course of mucopolysaccharidosis type IIIA (MPS IIIA), and identify potential endpoints for future treatment trials.

STUDY DESIGN

Children with a confirmed diagnosis of MPS IIIA, functioning above a developmental age of 1 year, were followed for up to 2 years. Cognitive status and brain atrophy were assessed by standardized tests and volumetric magnetic resonance imaging, respectively. Liver and spleen volumes and cerebrospinal fluid and urine biomarker levels were measured.

RESULTS

Twenty-five children, from 1.1 to 18.4 years old, were enrolled, and 24 followed for at least 12 months. 19 exhibited a rapidly progressing (RP) form of MPS IIIA, and 5, a more slowly progressing form. Children with RP plateaued in development by 30 months, followed by rapid regression after 40-50 months. In patients with RP, cognitive developmental quotients showed consistent steep declines associated with progressive cortical gray matter atrophy. Children with slowly progressing had a similar but more prolonged course. Liver and spleen volumes were approximately double normal size, and cerebrospinal fluid and urine heparin sulfate levels were elevated and relatively constant over time.

CONCLUSION

Developmental quotient and cortical gray matter volume are sensitive markers of disease progression in MPS IIIA, and may have utility as clinical endpoints in treatment trials. For optimal outcomes, treatment may need to be instituted in children before the onset of steep cognitive decline and brain atrophy.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT01047306.

The Neurobehavioral Phenotype in Mucopolysaccharidosis Type IIIB: an Exploratory Study

OBJECTIVES

Our goal was to describe the neurobehavioral phenotype in mucopolysaccharidosis Type IIIB (MPS IIIB). Parents report that behavioral abnormalities are a major problem in MPS III posing serious challenges to parenting and quality-of-life for both patient and parent. Our previous research on MPS IIIA identified autistic symptoms, and a Klüver-Bucy-type syndrome as indicated by reduced startle and loss of fear associated with amygdala atrophy. We hypothesized that MPS IIIB would manifest similar attributes when assessed with the same neurobehavioral protocol.

METHODS

Ten patients with MPS IIIB were compared with 9 MPS IIIA patients, all older than 6. 8 younger children with Hurler syndrome (1H) were chosen as a comparison group for the Risk Room procedure; MPS IH does not directly affect social/emotional function and these younger children were closer to the developmental level of the MPS IIIB group. To examine disease severity, cognitive ability was assessed. Four evaluations were used: the Risk Room procedure (to measure social-emotional characteristics, especially fear and startle responses), the Autism Diagnostic Observation Schedule (ADOS), the Sanfilippo Behavior Rating Scale (SBRS), and amygdala brain volumes calculated from manually-traced MRI images.

RESULTS

The two groups are equivalent in severity and show severe cognitive impairment. On the ADOS, the MPS IIIB patients exhibited the same autistic features as IIIA. The IIIB means differed from MPS IH means on most measures. However, the IIIB group did not approach the Risk Room stranger, like the MPS IH group who kept their distance, but unlike the IIIA group who showed no fear of the stranger. On the SBRS, the MPS IIIB patients were described as more inattentive and more fearful, especially of new people than the MPS IIIA. Onsets of some disease characteristics appeared more closely spaced and slightly earlier in MPS IIIB than IIIA.

CONCLUSIONS

On most behavioral measures, MPS IIIB patients did not differ substantially from MPS IIIA patients over age six, demonstrating autistic features and a Klüver Bucy-like syndrome including lack of fear and poor attention. Delay in onset of behavioral symptoms was associated with later diagnosis in two patients. Lack of fear, poor attention, and autistic-like symptomatology are as characteristic of MPS IIIB as they are of MPS IIIA. A possible difference is that the some behavioral abnormalities develop more quickly in MPS IIIB, If this is so, these patients may become at risk for harm and present a challenge for parenting even earlier than do those with MPS IIIA. .In future clinical trials of new treatments, especially with respect to quality of life and patient management, improvement of these behaviors will be an essential goal. Because very young patients were not studied, prospective natural history documentation of the early development of abnormal behaviors in MPS IIIB is needed.

Sanfilippo syndrome: causes, consequences, and treatments

Sanfilippo syndrome, or mucopolysaccharidosis (MPS) type III, refers to one of five autosomal recessive, neurodegenerative lysosomal storage disorders (MPS IIIA to MPS IIIE) whose symptoms are caused by the deficiency of enzymes involved exclusively in heparan sulfate degradation. The primary characteristic of MPS III is the degeneration of the central nervous system, resulting in mental retardation and hyperactivity, typically commencing during childhood. The significance of the order of events leading from heparan sulfate accumulation through to downstream changes in the levels of biomolecules within the cell and ultimately the (predominantly neuropathological) clinical symptoms is not well understood. The genes whose deficiencies cause the MPS III subtypes have been identified, and their gene products, as well as a selection of disease-causing mutations, have been characterized to varying degrees with respect to both frequency and direct biochemical consequences. A number of genetic and biochemical diagnostic methods have been developed and adopted by diagnostic laboratories. However, there is no effective therapy available for any form of MPS III, with treatment currently limited to clinical management of neurological symptoms. The availability of animal models for all forms of MPS III, whether spontaneous or generated via gene targeting, has contributed to improved understanding of the MPS III subtypes, and has provided and will deliver invaluable tools to appraise emerging therapies. Indeed, clinical trials to evaluate intrathecally-delivered enzyme replacement therapy in MPS IIIA patients, and gene therapy for MPS IIIA and MPS IIIB patients are planned or underway.

Actigraphic investigation of circadian rhythm functioning and activity levels in children with mucopolysaccharidosis type III (Sanfilippo syndrome)

BACKGROUND

Sleep disturbance is part of the behavioural phenotype of the rare genetic condition mucopolysaccharidosis (MPS) type III. A growing body of evidence suggests that underlying disturbance in circadian rhythm functioning may explain sleep problems within the MPS III population.

METHODS

Actigraphic data were recorded in eight children with MPS III over 7-10 days and compared to age-matched typically developing controls. Parameters of circadian rhythmicity and activity levels across a 24-h period were analysed.

RESULTS

Statistically and clinically significant differences between the two groups were noted. Analysis indicated that children with MPS III showed significantly increased fragmentation of circadian rhythm and reduced stability with external cues (zeitgebers), compared to controls. Average times of activity onset and offset were indicative of a phase delayed sleep-wake cycle for some children in the MPS III group. Children with MPS III had significantly higher activity levels during the early morning hours (midnight-6 am) compared to controls.

CONCLUSIONS

Results are consistent with previous research into MPS III and suggest that there is an impairment in circadian rhythm functioning in children with this condition. Implications for clinical practice and the management of sleep difficulties are discussed.

Sanfilippo syndrome: Overall review

Mucopolysaccharidosis type III (MPS III, Sanfilippo syndrome) is a lysosomal storage disorder, caused by a deficiency in one of the four enzymes involved in the catabolism of glycosaminoglycan heparan sulfate. It is characterized by progressive cognitive decline and severe hyperactivity, with relatively mild somatic features. This review focuses on clinical features, diagnosis, treatment, and follow-up of MPS III, and provides information about supplementary tests and differential diagnosis. Given that few reviews of MPS III have been published, several studies were compiled to establish diagnostic recommendations. Quantitative urinary glycosaminoglycan analysis is strongly recommended, and measurement of disaccharides, heparin cofactor II-thrombin complex and gangliosides is also used. Enzyme activity of the different enzymes in blood serum, leukocytes or fibroblasts, and mutational analysis for SGSH, NAGLU, HGSNAT or GNS genes are required to confirm diagnosis and differentiate four subtypes of MPS III. Although there is no global consensus for treatment, enzyme replacement therapy and gene therapy can provide appropriate results. In this regard, recent publications on treatment and follow-up are discussed.

Quantifying behaviors of children with Sanfilippo syndrome: the Sanfilippo Behavior Rating Scale

The Sanfilippo Behavior Rating Scale (SBRS), a 68 item questionnaire, has been developed to assess the behavioral phenotype of children with Sanfilippo syndrome and its progression over time. Fifteen scales rate orality, movement/activity, attention/self-control, emotional function including anger and fear, and social interaction. Items within scales intercorrelate; measures of internal consistency are adequate. Twelve scales are grouped into 4 abnormality clusters: Movement, Lack of fear, Social/emotional and Executive Dysfunction. A Loess age-trajectory analysis showed that Lack of Fear, Social/Emotional and Executive Dysfunction increased steadily with age; Orality and Mood/Anger/Aggression leveled off. Movement peaked around 6years, then declined as children's excessive/purposeless actions stopped. Compared with standard scales, SBRS Movement was appropriately associated with the Vineland Motor scale; SBRS Lack of Fear had significant associations with the Autism Diagnostic Observation Schedule (ADOS), indicating a symptom overlap between Sanfilippo syndrome and autism. This suggests that reduced fearfulness may be the most salient/sensitive SBRS marker of disease progression. Volumetric MRI showed that increased Lack of Fear was significantly associated with reduced amygdala volume, consistent with our hypothesis that the behavior seen in Sanfilippo syndrome is a variant of Klüver-Bucy syndrome. Hippocampal volume loss had twice the effect on Social-Emotional Dysfunction as amygdala loss, consistent with a hippocampal role in attachment and social emotions. In conclusion, the SBRS assesses the Sanfilippo behavioral phenotype; it can measure behavior change that accompanies disease progression and/or results from treatment.

A multiparametric computational algorithm for comprehensive assessment of genetic mutations in mucopolysaccharidosis type IIIA (Sanfilippo syndrome)

Mucopolysaccharidosis type IIIA (MPS-IIIA, Sanfilippo syndrome) is a Lysosomal Storage Disease caused by cellular deficiency of N-sulfoglucosamine sulfohydrolase (SGSH). Given the large heterogeneity of genetic mutations responsible for the disease, a comprehensive understanding of the mechanisms by which these mutations affect enzyme function is needed to guide effective therapies. We developed a multiparametric computational algorithm to assess how patient genetic mutations in SGSH affect overall enzyme biogenesis, stability, and function. 107 patient mutations for the SGSH gene were obtained from the Human Gene Mutation Database representing all of the clinical mutations documented for Sanfilippo syndrome. We assessed each mutation individually using ten distinct parameters to give a comprehensive predictive score of the stability and misfolding capacity of the SGSH enzyme resulting from each of these mutations. The predictive score generated by our multiparametric algorithm yielded a standardized quantitative assessment of the severity of a given SGSH genetic mutation toward overall enzyme activity. Application of our algorithm has identified SGSH mutations in which enzymatic malfunction of the gene product is specifically due to impairments in protein folding. These scores provide an assessment of the degree to which a particular mutation could be treated using approaches such as chaperone therapies. Our multiparametric protein biogenesis algorithm advances a key understanding in the overall biochemical mechanism underlying Sanfilippo syndrome. Importantly, the design of our multiparametric algorithm can be tailored to many other diseases of genetic heterogeneity for which protein misfolding phenotypes may constitute a major component of disease manifestation.

An investigation of the middle and late behavioural phenotypes of Mucopolysaccharidosis Type-III

Background

Mucopolysaccharidosis type-III (MPS III) is an autosomal recessive lysosomal storage disorder. It causes progressive physical and cognitive decline and has been linked to increased incidences of behavioural problems.

Methods

Data on the behaviour and adaptive skills of 20 children with MPS III and 25 children with intellectual disability (ID) (17 included in analysis) were gathered via parental report questionnaire. The frequencies of different types of behaviour displayed by children with MPS III and children with ID were compared across two age categories.

Results

The total frequency of challenging behaviours displayed by children aged 2–9 years with MPS III and ID was not significantly different. Behaviours associated with hyperactivity, orality, unusual body movements and inattention were seen significantly more frequently in 2–9 year olds with MPS III than in those with ID. Children aged 10–15 years with MPS III showed significantly fewer problem behaviours than a contrasting group with ID. The frequency of challenging behaviours displayed by children with MPS III and their adaptive skills was found to decrease with age.

Conclusions

Behaviours relating to hyperactivity, orality, unusual body movements and inattention are part of the behavioural phenotype of the middle phase of MPS III. The late phase of MPS III is associated with low rates of problem behaviour and loss of adaptive skills. Therefore, families with a child with MPS III may benefit from a different type of clinical service when the child is aged 2–9 years, than when aged 10–15 years.

The laboratory diagnosis of mucopolysaccharidosis III (Sanfilippo syndrome): A changing landscape

Mucopolysaccharidosis type III (MPS III) is characterized by progressive neurological deterioration, behavioral abnormalities, a relatively mild somatic phenotype, and early mortality. Because of the paucity of somatic manifestations and the rarity of the disease, early diagnosis is often difficult. Therapy targeting the underlying disease pathophysiology may offer the greatest clinical benefit when started prior to the onset of significant neurologic sequelae. Here we review current practices in the laboratory diagnosis of MPS III in order to facilitate earlier patient identification and diagnosis. When clinical suspicion of MPS III arises, the first step is to order a quantitative assay that screens urine for the presence of glycosaminoglycan biomarkers using a spectrophotometric compound (e.g., dimethylmethylene blue). We recommend testing all patients with developmental delay and/or behavioral abnormalities as part of the diagnostic work-up because quantitative urine screening is inexpensive and non-invasive. Semi-quantitative urine screening assays using cationic dyes on filter paper (e.g., spot tests) have relatively high rates of false-positives and false-negatives and are obsolete. Of note, a negative urinary glycosaminoglycan assay does not necessarily rule out MPS because, in some patients, an overlap in excretion levels with healthy controls may occur. All urine samples that test positive for glycosaminoglycans with a quantitative assay should be confirmed by electrophoresis, thin layer chromatography, or tandem mass spectrometry, which further improves the sensitivity and specificity. The gold standard for diagnosis remains the enzyme activity assay in cultured skin fibroblasts, leukocytes, plasma, or serum, which can be used as a first-line diagnostic test in some regions. Molecular genetic analysis should be offered to all families of patients to allow genetic counseling for informed family planning. For a small number of variants, genotype-phenotype correlations are available and can offer prognostic value. Prenatal testing via enzyme activity assay in chorionic villi or amniotic fluid cells is available at a limited number of centers worldwide, but whenever possible, a molecular genetic analysis is preferred for prenatal diagnosis. To conclude, we discuss the development of newborn screening assays in dried blood spots and high-throughput methods for sequencing the protein-coding regions of the genome (whole exome sequencing) and their relevance to future changes in the MPS III diagnostic landscape.

Intracerebral administration of adeno-associated viral vector serotype rh.10 carrying human SGSH and SUMF1 cDNAs in children with mucopolysaccharidosis type IIIA disease: results of a phase I/II trial

Mucopolysaccharidosis type IIIA is a severe degenerative disease caused by an autosomal recessive defect of a gene encoding a lysosomal heparan-N-sulfamidase, the N-sulfoglycosamine sulfohydrolase (SGSH), the catalytic site of which is activated by a sulfatase-modifying factor (SUMF1). Four children (Patients 1-3, aged between 5.5 and 6 years; Patient 4 aged 2 years 8 months) received intracerebral injections of an adeno-associated viral vector serotype rh.10-SGSH-IRES-SUMF1 vector in a phase I/II clinical trial. All children were able to walk, but their cognitive abilities were abnormal and had declined (Patients 1-3). Patients 1-3 presented with brain atrophy. The therapeutic vector was delivered in a frameless stereotaxic device, at a dose of 7.2×10(11) viral genomes/patient simultaneously via 12 needles as deposits of 60 μl over a period of 2 hr. The vector was delivered bilaterally to the white matter anterior, medial, and posterior to the basal ganglia. Immunosuppressive treatment (mycophenolate mofetil and tacrolimus) was initiated 15 days before surgery and maintained for 8 weeks (mycophenolate mofetil) or throughout follow-up (tacrolimus, with progressive dose reduction) to prevent elimination of transduced cells. Safety data collected from inclusion, during the neurosurgery period and over the year of follow-up, showed good tolerance, absence of adverse events related to the injected product, no increase in the number of infectious events, and no biological sign of toxicity related to immunosuppressive drugs. Efficacy analysis was necessarily preliminary in this phase I/II trial on four children, in the absence of validated surrogate markers. Brain atrophy evaluated by magnetic resonance imaging seemed to be stable in Patients 1 and 3 but tended to increase in Patients 2 and 4. Neuropsychological evaluations suggested a possible although moderate improvement in behavior, attention, and sleep in Patients 1-3. The youngest patient was the most likely to display neurocognitive benefit.

Acquired autistic behaviors in children with mucopolysaccharidosis type IIIA

OBJECTIVES

To assess autism spectrum disorder (ASD) behaviors in children with mucopolysaccharidosis type IIIA (MPS IIIA) using a standard measure, understand the behavioral evolution of the disease, and provide specific guidelines for diagnosis.

STUDY DESIGN

Children (n = 21) with documented enzyme deficiency and SGSH gene mutations, cognitive age-equivalent >12 months, and early onset were administered the Autism Diagnostic Observation Schedule (ADOS) (module 1) and Bayley Scales of Infant Development-Third Edition. ADOS Social Affect and Restricted Repetitive Behavior total scores, as well as Bayley Scales of Infant Development-Third Edition cognitive age-equivalent scores, are reported using descriptive statistics and graphic presentations.

RESULTS

Thirteen of the 21 children evaluated met the ADOS criteria for ASD/autism. ADOS score was strongly associated with age; all 11 children aged >46 months met the criteria, compared with only 2 of 10 aged <46 months. Social and affective abnormalities were most frequent; restricted interests and repetitive behaviors were largely absent. Lack of cognitive growth paralleled ADOS score.

CONCLUSION

An increased incidence of ASD-like social behaviors was seen at age 3-4 years in children with early-onset MPS IIIA. Although more frequent in the severely impaired children, ASD-like behaviors were observed across the entire range of cognitive impairment. Clinicians must be aware that when a child acquires ASD-like behaviors, MPS IIIA should be included in the differential diagnosis.

Structure of sulfamidase provides insight into the molecular pathology of mucopolysaccharidosis IIIA

Mucopolysaccharidosis type IIIA (Sanfilippo A syndrome), a fatal childhood-onset neurodegenerative disease with mild facial, visceral and skeletal abnormalities, is caused by an inherited deficiency of the enzyme N-sulfoglucosamine sulfohydrolase (SGSH; sulfamidase). More than 100 mutations in the SGSH gene have been found to reduce or eliminate its enzymatic activity. However, the molecular understanding of the effect of these mutations has been confined by a lack of structural data for this enzyme. Here, the crystal structure of glycosylated SGSH is presented at 2 Å resolution. Despite the low sequence identity between this unique N-sulfatase and the group of O-sulfatases, they share a similar overall fold and active-site architecture, including a catalytic formylglycine, a divalent metal-binding site and a sulfate-binding site. However, a highly conserved lysine in O-sulfatases is replaced in SGSH by an arginine (Arg282) that is positioned to bind the N-linked sulfate substrate. The structure also provides insight into the diverse effects of pathogenic mutations on SGSH function in mucopolysaccharidosis type IIIA and convincing evidence for the molecular consequences of many missense mutations. Further, the molecular characterization of SGSH mutations will lay the groundwork for the development of structure-based drug design for this devastating neurodegenerative disorder.

Natural history of Sanfilippo syndrome type A

OBJECTIVE

To describe the natural history of Sanfilippo syndrome type A.

METHODS

We performed a retrospective review of 46 children (21 boys, 25 girls) with Sanfilippo syndrome type A evaluated between January 2000 and April 2013. Assessments included neurodevelopmental evaluations, audiologic testing, and assessment of growth, adaptive behavior, cognitive behavior, motor function, and speech/language skills. Only the baseline evaluation was included for patients who received hematopoietic stem cell transplantation.

RESULTS

Median age at diagnosis was 35 months, with a median delay between initial symptoms to diagnosis of 24 months. The most common initial symptoms were speech/language delay (48%), dysmorphology (22%), and hearing loss (20%). Early behavioral problems included perseverative chewing and difficulty with toilet training. All children developed sleep difficulties and behavioral changes (e.g., hyperactivity, aggression). More than 93% of the children experienced somatic symptoms such as hepatomegaly (67%), abnormal dentition (39%), enlarged tongue (37%), coarse facial features (76%), and protuberant abdomen (43%). Kaplan-Meier analysis showed a 60% probability of surviving past 17 years of age.

CONCLUSIONS

Sanfilippo type A is characterized by severe hearing loss and speech delay, followed by a rapid decline in cognitive skills by 3 years of age. Significant somatic disease occurs in more than half of patients. Behavioral difficulties presented between 2 and 4 years of age during a rapid period of cognitive decline. Gross motor abilities are maintained during this period, which results in an active child with impaired cognition. Sleep difficulties are concurrent with the period of cognitive degeneration. There is currently an unacceptable delay in diagnosis, highlighting the need to increase awareness of this disease among clinicians.