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

People with intellectual disability: what do we know about adulthood and life expectancy?

Increases in the life expectancy of people with Intellectual Disability have followed similar trends to those found in the general population. With the exception of people with severe and multiple disabilities or Down syndrome, the life expectancy of this group now closely approximates with that of the general population. Middle and old age, which until 30 years ago were not recognized in this population, are now important parts of the life course of these individuals. Older adults with Intellectual Disabilities form a small, but significant and growing proportion of older people in the community. How these persons grow older and how symptoms and complications of the underlying cause of the Intellectual Disability will influence their life expectancy is of the utmost importance.

Assessment of sleep in children with mucopolysaccharidosis type III

Sleep disturbances are prevalent in mucopolysaccharidosis Type III (MPS III), yet there is a lack of objective, ecologically valid evidence detailing sleep quantity, quality or circadian system. Eight children with MPS III and eight age-matched typically developing children wore an actigraph for 7–10 days/nights. Saliva samples were collected at three time-points on two separate days, to permit analysis of endogenous melatonin levels. Parents completed a sleep questionnaire and a daily sleep diary. Actigraphic data revealed that children with MPS III had significantly longer sleep onset latencies and greater daytime sleep compared to controls, but night-time sleep duration did not differ between groups. In the MPS III group, sleep efficiency declined, and sleep onset latency increased, with age. Questionnaire responses showed that MPS III patients had significantly more sleep difficulties in all domains compared to controls. Melatonin concentrations showed an alteration in the circadian system in MPS III, which suggests that treatment for sleep problems should attempt to synchronise the sleep-wake cycle to a more regular pattern. Actigraphy was tolerated by children and this monitoring device can be recommended as a measure of treatment success in research and clinical practice.

Natural history of Sanfilippo syndrome in Spain

Background

Mucopolysaccharidosis type III (MPS III), or Sanfilippo syndrome, is caused by a deficiency in one of the four enzymes involved in the lysosomal degradation of heparan sulphate. Four MPS III types have been recognized, characterized by a large phenotypic heterogeneity. This is the first Spanish study describing the natural history of Sanfilippo patients (MPSIIIA, MPSIIIB and MPSIIIC), representing an essential step for understanding patient prognosis and for the establishment and application of future therapies.

Methods

This retrospective study aimed to establish the natural history of MPS III in Spain based on an extensive chronological data survey involving physicians and parents of 55 Spanish MPSIII patients. In addition to clinical description we report biochemical and molecular analysis already performed in the majority of cases.

Results

The most frequent subtype was MPS IIIA (62%). Symptoms before diagnosis were speech delay in 85%, followed by coarse facial features in 78%, and hyperactivity in 65% of cases at a mean age of 3 years old. The median age at clinical and biochemical diagnosis for each MPS III subtype were as follows: IIIA 4.4 years (1.2 – 16 years), IIIB 3.1 years (1–29 years), and IIIC 6.3 years (3.4-22 years).

45% of patients developed epilepsy at a median age of 8.7 (2.5 – 37) years old.

Age of death for MPS IIIA patients was 15 years (11.5 – 26 years).

Molecular analysis of our cohort reveals, as alluded to above, a great allelic heterogeneity in the three subtypes without clear genotype-phenotype correlations in most cases.

Conclusion

MPS IIIA is the most frequent subtype in Spanish Sanfilippo patients. Diagnosing physicians should consider Sanfilippo syndrome in children with non-specific speech delay, behavioural abnormalities, and/or mild dysmorphic features. We stress the importance of establishing early diagnosis procedures as soon as possible so as to be able to determine future short-term enzymatic or gene therapy treatments that can change the prognosis of the disease.

Methods of neurodevelopmental assessment in children with neurodegenerative disease: Sanfilippo syndrome

OBJECTIVES

(1) Develop a methodology for obtaining reliable cognitive and developmental data in children with neurodegenerative disease and cognitive impairment and in turn monitor disease state and treatment outcomes. (2) Demonstrate validity of age-equivalent scores.

METHODS

We present guidelines for obtaining accurate test scores in low-functioning and behaviorally disruptive pediatric patients, followed by a method validation study: (1) using disease-specific protocols to assess salient aspects of the known phenotype, (2) selecting appropriate tests, (3) managing behavior, and (4) using age-equivalent scores on standardized tools. We used the Bayley Scales of Infant Development-III or Kaufman Assessment Battery for Children-II with a group of 25 children with mucopolysaccharidosis type IIIA (MPS IIIA or Sanfilippo syndrome type A) with dementia. To demonstrate concurrent validity, we used the Vineland Adaptive Behavior Scales-II, comparing parent-reported age-equivalent scores (AEs) with those of the cognitive measures.

RESULTS

We were successful in obtaining cognitive age-equivalents for 25 patients with MPS IIIA including those with severe behavioral disruption and a correlation of 0.95 was obtained comparing scores on the parent measure with cognitive age-equivalents validating the age-equivalent approach.

CONCLUSION

An approach to the assessment of severely impaired children including those with behavioral disruption was implemented and is applicable to children with other severe neurological diseases. This approach will enhance the assessment of disease progression and monitoring of treatment outcome in clinical trials.

A rapid and sensitive method for measuring N-acetylglucosaminidase activity in cultured cells

A rapid and sensitive method to quantitatively assess N-acetylglucosaminidase (NAG) activity in cultured cells is highly desirable for both basic research and clinical studies. NAG activity is deficient in cells from patients with Mucopolysaccharidosis type IIIB (MPS IIIB) due to mutations in NAGLU, the gene that encodes NAG. Currently available techniques for measuring NAG activity in patient-derived cell lines include chromogenic and fluorogenic assays and provide a biochemical method for the diagnosis of MPS IIIB. However, standard protocols require large amounts of cells, cell disruption by sonication or freeze-thawing, and normalization to the cellular protein content, resulting in an error-prone procedure that is material- and time-consuming and that produces highly variable results. Here we report a new procedure for measuring NAG activity in cultured cells. This procedure is based on the use of the fluorogenic NAG substrate, 4-Methylumbelliferyl-2-acetamido-2-deoxy-alpha-D-glucopyranoside (MUG), in a one-step cell assay that does not require cell disruption or post-assay normalization and that employs a low number of cells in 96-well plate format. We show that the NAG one-step cell assay greatly discriminates between wild-type and MPS IIIB patient-derived fibroblasts, thus providing a rapid method for the detection of deficiencies in NAG activity. We also show that the assay is sensitive to changes in NAG activity due to increases in NAGLU expression achieved by either overexpressing the transcription factor EB (TFEB), a master regulator of lysosomal function, or by inducing TFEB activation chemically. Because of its small format, rapidity, sensitivity and reproducibility, the NAG one-step cell assay is suitable for multiple procedures, including the high-throughput screening of chemical libraries to identify modulators of NAG expression, folding and activity, and the investigation of candidate molecules and constructs for applications in enzyme replacement therapy, gene therapy, and combination therapies.

Mucopolysaccharidosis Type IIIA presents as a variant of Klüver-Bucy syndrome

Mucopolysaccharidosis Type IIIA (MPS IIIA) is a neurodegenerative disease with behavioral symptoms unique among the mucopolysaccharidoses. Children with MPS IIIA reportedly mouth things, explore novel environments almost continuously, disregard danger, and empathize/socialize and comply less with parents. These characteristics resemble Klüver-Bucy syndrome (K-Bs). To test the K-Bs hypothesis, 30 children with MPS IIIA were compared to 8 "posttransplant" mucopolysaccharidosis Type IH patients in an experimental "risk room." The room contained attractive and mildly frightening objects, exposure to a 92-dB startle noise triggered by contact with an attractive toy, mother's return after a brief absence, and compliance with her cleanup directive. Children with MPS IIIA: (a) left mother sooner, (b) wandered more, (c) were more likely to approach frightening objects, (d) were less likely to respond to loud noise with whole body startle, (e) were less likely to avoid the toy associated with the startle noise, (f) interacted less with mother upon her return, and (g) complied less with her cleanup command. K-Bs is associated with loss of amygdala function. Brain magnetic resonance imaging (MRI) of a subset of the children with MPS IIIA showed volume loss that was greater in the amygdala than in the hippocampus; only amygdala loss correlated with reduced fearfulness. MPS IIIA may be the first identified pediatric disease presenting systematically as a K-Bs variant. If validated by further studies, the K-Bs hypothesis of MPS IIIA would provide important clinical and theoretical information for the guidance of families as well as markers for natural disease progression and treatment effects.

Myeloid/Microglial driven autologous hematopoietic stem cell gene therapy corrects a neuronopathic lysosomal disease

Mucopolysaccharidosis type IIIA (MPSIIIA) is a lysosomal storage disorder caused by mutations in N-sulfoglucosamine sulfohydrolase (SGSH), resulting in heparan sulfate (HS) accumulation and progressive neurodegeneration. There are no treatments. We previously demonstrated improved neuropathology in MPSIIIA mice using lentiviral vectors (LVs) overexpressing SGSH in wild-type (WT) hematopoietic stem cell (HSC) transplants (HSCTs), achieved via donor monocyte/microglial engraftment in the brain. However, neurological disease was not corrected using LVs in autologous MPSIIIA HSCTs. To improve brain expression via monocyte/microglial specificity, LVs expressing enhanced green fluorescent protein (eGFP) under ubiquitous phosphoglycerate kinase (PGK) or myeloid-specific promoters were compared in transplanted HSCs. LV-CD11b-GFP gave significantly higher monocyte/B-cell eGFP expression than LV-PGK-GFP or LV-CD18-GFP after 6 months. Subsequently, autologous MPSIIIA HSCs were transduced with either LV-PGK-coSGSH or LV-CD11b-coSGSH vectors expressing codon-optimized SGSH and transplanted into MPSIIIA mice. Eight months after HSCT, LV-PGK-coSGSH vectors produced bone marrow SGSH (576% normal activity) similar to LV-CD11b-coSGSH (473%), but LV-CD11b-coSGSH had significantly higher brain expression (11 versus 7%), demonstrating improved brain specificity. LV-CD11b-coSGSH normalized MPSIIIA behavior, brain HS, GM2 ganglioside, and neuroinflammation to WT levels, whereas LV-PGK-coSGSH partly corrected neuropathology but not behavior. We demonstrate compelling evidence of neurological disease correction using autologous myeloid driven lentiviral-HSC gene therapy in MPSIIIA mice.

Mucopolysaccharidosis type III (Sanfilippo syndrome) and misdiagnosis of idiopathic developmental delay, attention deficit/hyperactivity disorder or autism spectrum disorder

Mucopolysaccharidosis III is a rare genetic disease characterized by progressive cognitive decline and severe hyperactivity that does not respond to stimulants. Somatic features are relatively mild. Patients are often initially misdiagnosed as having idiopathic developmental delay, attention deficit/hyperactivity disorder and/or autism spectrum disorders, putting them at risk for unnecessary testing and treatments.

Conclusion: Children with developmental or speech delay, especially those with a characteristic somatic feature or behavioural abnormalities, should be screened for MPS III.

A novel mutation (c.200T>C) in the NAGLU gene of a Korean patient with mucopolysaccharidosis IIIB

Mucopolysaccharidosis (MPS) IIIB is a lysosomal storage disorder (LSD) caused by abnormalities of the enzyme α-N-acetylglucosaminidase (NAGLU) that is required for degradation of heparan sulfate. The patient in this study was a 4-yr-old boy. He presented with normal height and weight, pectus carinatum, and multiple persistent Mongolian spots on his back. He had mild dysmorphic features with prominent speech developmental delays and, to a lesser extent, motor developmental delays. The cetylpyridinium chloride precipitation test revealed excessive mucopolysacchariduria (657.2 mg glycosaminoglycan/g creatinine; reference range, <175 mg glycosaminoglycan/g creatinine). Thin layer chromatography showed urinary heparan sulfate excretion. NAGLU enzyme activity was significantly decreased in leukocytes (not detected; reference range, 0.9-1.51 nmol/hr/mg protein) as well as in plasma (0.14 nmol/hr/mg protein; reference range, 22.3-60.9 nmol/hr/mg protein). PCR and direct sequencing analysis of the NAGLU gene showed that the patient was a compound heterozygote for 2 mutations: c.200T>C (p.L67P) and c.1444C>T (p.R482W). The c.200T>C mutation was a novel finding. This is the first report of a Korean patient with MPS IIIB who was confirmed by molecular genetic analyses and biochemical investigation.

Heparan sulfate derived disaccharides in plasma and total urinary excretion of glycosaminoglycans correlate with disease severity in Sanfilippo disease

BACKGROUND

Sanfilippo disease (Mucopolysaccharidosis III) is a neurodegenerative lysosomal disorder characterized by accumulation of the glycosaminoglycan heparan sulfate (HS). MPS III has a large phenotypic variability and early assessment of disease severity is difficult. We investigated the correlation between disease severity and the plasma concentration of HS (pHS, defined by the sum of the heparan sulfate derived disaccharides obtained after enzymatic digestion) and urinary total GAGs level (uGAGs, measured by the dimethylene blue test) in a cross-sectional cohort of 44 MPS III patients.

METHODS

Disease severity was established on the basis of the age of complete loss of independent walking and of full loss of speech in all patients. Hazard ratios (HR) were obtained with cox-regression analysis. In order to allow prediction of a severe phenotype based on a cut-off value for pHS, patients were divided in two groups (severely affected and less severely affected) based on predictive mutations or on the age of full loss of speech. Receiver operator characteristics (ROC) were obtained for pHS.

RESULTS

pHS and uGAGs were independently and linearly associated with an increased risk of speech loss with a HR of 1.8 (95 % CI 1.3-2.7) per 500 ng/ml increase of HS in plasma (p = 0.002), and a HR of 2.7 (95 % CI 1.6-4.4) per 10 mg/mmol creatinine increase of uGAGs (p < 0.001). pHS and uGAGS were less strongly associated with loss of walking. The area under the ROC curve for pHS was 0.85, indicating good discrimination.

CONCLUSION

pHS and uGAGs may be useful biomarkers for prediction of severity in MPS III.

Behavioural phenotypes of the mucopolysaccharide disorders: a systematic literature review of cognitive, motor, social, linguistic and behavioural presentation in the MPS disorders

BACKGROUND

The mucopolysaccharide disorders (MPS) are a group of recessively inherited metabolic disorders resulting in progressive physical and cognitive decline.

MATERIALS AND METHODS

MEDLINE, PsycINFO and Embase databases were searched, alongside manual screening, to identify relevant literature. Papers were included in the review if they were published in a peer reviewed journal and conducted empirical research into cognitive, motor, social or linguistic development or behaviour in one or more MPS disorders.

RESULTS

Twenty-five papers were reviewed. Two papers used methodology of a sufficiently high standard to demonstrate a behavioural phenotype; both found sleep disturbance to be part of the phenotype of MPS III. Fearfulness and sleep disturbance were frequently observed in people with MPS I and II. Cognitive and motor impairment and decline, and challenging behaviour were highly prevalent in the severe form of MPS II. Cognitive decline and severe behavioural problems relating to aggression, hyperactivity, orality, unusual affect and temper tantrums were seen in MPS III.

CONCLUSIONS

Sleep disturbance is part of the behavioural phenotype of MPS III, and challenging behaviour is highly prevalent in MPS II and MPS III, therefore the efficacy of behavioural interventions for these populations should be investigated. Further research into the behaviour and adaptive skills of children with MPS III and MPS IV is required.

Hematopoietic stem cell and gene therapy corrects primary neuropathology and behavior in mucopolysaccharidosis IIIA mice

Mucopolysaccharidosis IIIA (MPS IIIA or Sanfilippo disease) is a neurodegenerative disorder caused by a deficiency in the lysosomal enzyme sulfamidase (SGSH), catabolizing heparan sulfate (HS). Affected children present with severe behavioral abnormalities, sleep disturbances, and progressive neurodegeneration, leading to death in their second decade. MPS I, a similar neurodegenerative disease accumulating HS, is treated successfully with hematopoietic stem cell transplantation (HSCT) but this treatment is ineffectual for MPS IIIA. We compared HSCT in MPS IIIA mice using wild-type donor cells transduced ex vivo with lentiviral vector-expressing SGSH (LV-WT-HSCT) versus wild-type donor cell transplant (WT-HSCT) or lentiviral-SGSH transduced MPS IIIA cells (LV-IIIA-HSCT). LV-WT-HSCT results in 10% of normal brain enzyme activity, near normalization of brain HS and GM2 gangliosides, significant improvements in neuroinflammation and behavioral correction. Both WT-HSCT and LV-IIIA-HSCT mediated improvements in GM2 gangliosides and neuroinflammation but were less effective at reducing HS or in ameliorating abnormal HS sulfation and had no significant effect on behavior. This suggests that HS may have a more significant role in neuropathology than neuroinflammation or GM2 gangliosides. These data provide compelling evidence for the efficacy of gene therapy in conjunction with WT-HSCT for neurological correction of MPS IIIA where conventional transplant is ineffectual.

Female mucopolysaccharidosis IIIA mice exhibit hyperactivity and a reduced sense of danger in the open field test

Reliable behavioural tests in animal models of neurodegenerative diseases allow us to study the natural history of disease and evaluate the efficacy of novel therapies. Mucopolysaccharidosis IIIA (MPS IIIA or Sanfilippo A), is a severe, neurodegenerative lysosomal storage disorder caused by a deficiency in the heparan sulphate catabolising enzyme, sulfamidase. Undegraded heparan sulphate accumulates, resulting in lysosomal enlargement and cellular dysfunction. Patients suffer a progressive loss of motor and cognitive function with severe behavioural manifestations and premature death. There is currently no treatment. A spontaneously occurring mouse model of the disease has been described, that has approximately 3% of normal enzyme activity levels. Behavioural phenotyping of the MPS IIIA mouse has been previously reported, but the results are conflicting and variable, even after full backcrossing to the C57BL/6 background. Therefore we have independently backcrossed the MPS IIIA model onto the C57BL/6J background and evaluated the behaviour of male and female MPS IIIA mice at 4, 6 and 8 months of age using the open field test, elevated plus maze, inverted screen and horizontal bar crossing at the same circadian time point. Using a 60 minute open field, we have demonstrated that female MPS IIIA mice are hyperactive, have a longer path length, display rapid exploratory behaviour and spend less time immobile than WT mice. Female MPS IIIA mice also display a reduced sense of danger and spend more time in the centre of the open field. There were no significant differences found between male WT and MPS IIIA mice and no differences in neuromuscular strength were seen with either sex. The altered natural history of behaviour that we observe in the MPS IIIA mouse will allow more accurate evaluation of novel therapeutics for MPS IIIA and potentially other neurodegenerative disorders.

Should metabolic diseases be systematically screened in nonsyndromic autism spectrum disorders?

Background

In the investigation of autism spectrum disorders (ASD), a genetic cause is found in approximately 10–20%. Among these cases, the prevalence of the rare inherited metabolic disorders (IMD) is unknown and poorly evaluated. An IMD responsible for ASD is usually identified by the associated clinical phenotype such as dysmorphic features, ataxia, microcephaly, epilepsy, and severe intellectual disability (ID). In rare cases, however, ASD may be considered as nonsyndromic at the onset of a related IMD.

Objectives

To evaluate the utility of routine metabolic investigations in nonsyndromic ASD.

Patients and Methods

We retrospectively analyzed the results of a metabolic workup (urinary mucopolysaccharides, urinary purines and pyrimidines, urinary creatine and guanidinoacetate, urinary organic acids, plasma and urinary amino acids) routinely performed in 274 nonsyndromic ASD children.

Results

The metabolic parameters were in the normal range for all but 2 patients: one with unspecific creatine urinary excretion and the other with persistent 3-methylglutaconic aciduria.

Conclusions

These data provide the largest ever reported cohort of ASD patients for whom a systematic metabolic workup has been performed; they suggest that such a routine metabolic screening does not contribute to the causative diagnosis of nonsyndromic ASD. They also emphasize that the prevalence of screened IMD in nonsyndromic ASD is probably not higher than in the general population (<0.5%). A careful clinical evaluation is probably more reasonable and of better medical practice than a costly systematic workup.