Mortality and cause of death in mucopolysaccharidosis type II—a historical review based on data from the Hunter Outcome Survey (HOS)

Summary  Mucopolysaccharidosis type II (MPS II or Hunter syndrome) is a progressive, multisystemic disease caused by a deficiency of iduronate-2-sulfatase. Patients with the severe form of the disease have cognitive impairment and typically die in the second decade of life. Patients with the less severe form do not experience significant cognitive involvement and may survive until the fifth or sixth decade of life. We studied the relationship of both severity of MPS II and the time period in which patients died with age at death in 129 patients for whom data were entered retrospectively into HOS (Hunter Outcome Survey), the only large-scale, multinational observational study of patients with MPS II. Median age at death was significantly lower in patients with cognitive involvement compared with those without cognitive involvement (11.7 versus 14.1 years; p = 0.024). These data indicate that cognitive involvement is indicative of more severe disease and lower life expectancy in patients with MPS II. Median age at death was significantly lower in patients who died in or before 1985 compared with those who died after 1985 (11.3 versus 14.1 years; p α 0.001). The difference in age at death between patients dying in or before, relative to after, the selected cut-off date of 1985 may reflect improvements in patient identification, care and management over the past two decades. Data from patients who died after 1985 could serve as a control in analyses of the effects of enzyme replacement therapy with idursulfase on mortality in patients with MPS II. Competing Interests: HOS is supported by Shire HGT, Inc., which is responsible for maintaining the central database and for performing statistical analyses at the request of the HOS advisory board. Shire HGT had no role in the interpretation of data. Editorial assistance to the authors was provided by Oxford PharmaGenesis™ Ltd and was paid for by Shire HGT, Inc. References to electronic databases. Mucopolysaccharidosis type II (MPS II, Hunter syndrome: OMIM +309900. Iduronate-2-sulfatase: EC 3.1.6.13. References to electronic databases: Mucopolysaccharidosis type II (MPS II, Hunter syndrome: OMIM +309900. Iduronate-2-sulfatase: EC 3.1.6.13.     

Intellectual and neurological functioning in Morquio syndrome (MPS IVa)

Mucopolysaccharidosis type IVa (MPS IVa, Morquio syndrome OMIM #253000) is a lysosomal storage disease caused by deficiency in N-acetylgalactosamine-6-sulfatase (GALNS, EC 3.1.6.4; encoded by GALNS gene at 16q24.3). Unlike other MPS disorders involving excessive heparan and dermatan sulfate, Morquio syndrome has not been associated with neurological involvement nor with intellectual impairment as this disorder of keratan sulfate has been described as a purely visceral and skeletal disorder. Neurocognitive assessment was undertaken of MPS IVa patients with age appropriate intellectual tests as well as a Child Behaviour Checklist as part of clinical follow up. Available neuroimaging studies (MRI and MR spectroscopy) were reviewed. Whilst more than half of the overall IQ scores fell in the average range, scores for 3/8 children fell below average. A number of behavioural problems were highlighted, including anxiety/depression, attention and somatic complaints. Subtle neuroimaging abnormalities were demonstrated in over half of the children. These findings present a challenge to existing assumptions about the nature of Morquio A syndrome. A hypothesis regarding the potential role of calcium signalling is explored.     

The characterization of a murine model of mucopolysaccharidosis II (Hunter syndrome)

Summary Mucopolysaccharidosis II (MPS II, Hunter syndrome in humans) is an X-linked inherited lysosomal storage disease caused by a deficiency in the lysosomal enzyme iduronate-2-sulfatase (I2S). I2S catalyses a step in the catabolism of glycosaminoglycans (GAGs) dermatan sulfate and heparan sulfate, and when it is deficient or absent GAGs accumulate in tissues and organs. Male knockout mice (IdS-KO), which lack the gene coding for I2S, exhibit many of the characteristics seen in the human disease. Compared to wild-type control mice, urine GAG excretion was elevated at 4 weeks of age and remained high throughout the lifespan, and tissue GAG levels were elevated as early as 7 weeks of age. Liver, spleen and other organs were significantly larger in the IdS-KO mice than in the wild-type. Radiographic examination revealed sclerosis and enlargement of the skull at 4 weeks of age and appendicular bone enlargement at 10–13 weeks of age. Micro CT scans showed severe periosteal bone formation at the lateral aspect of the distal tibia and calcification of the calcaneus tendon. This model was used in the development of idursulfase for treatment of MPS II and may continue to be useful in the evaluation of treatment strategies of this chronic and progressive disorder. Competing interests: A.R. Garcia, J. Pan and J.C. Lamsa are employees of Shire Human Genetic Therapies, Inc. J. Muenzer has been a consultant to Shire HGT during the development of idursulfase for the treatment of MPS II. Editorial assistance was provided by Edward Weselcouch and was paid for by Shire HGT. References to electronic databases: Iduronate-2-sulfatase: EC 3.1.6.13. Mucopolysaccharidosis II (Hunter syndrome): OMIM 309900. .     

Attenuated osteoarticular phenotype of type VI mucopolysaccharidosis: a report of four patients and a review of the literature

Mucopolysaccharidosis type VI (Maroteaux–Lamy syndrome, MPS VI, OMIM 253200) is caused by mutations in the gene coding for N-acetylgalactosamine-4-sulfatase (4-sulfatase, arylsulfatase B, ARSB, EC 3.1.6.12), a lysosomal enzyme involved in the degradation of dermatan sulfate (DS). The clinical presentation of MPS VI varies greatly with respect to age of onset and rate of disease progression. This report focuses on the attenuated form of MPS VI, which can go unrecognized for years and often presents with atypical signs or symptoms. We described a cohort of MPS VI patients (n?=?4) heterozygous for the p.Y210C mutation who had a significant osteoarticular involvement at the onset of their disease and who were diagnosed years or even decades later. We have also reviewed the literature (n?=?36). Two types of attenuated MPS VI phenotypes could be distinguished: osteoarticular and cardiac. The majority of MPS VI patients reported so far as relatively attenuated presented with an essentially osteoarticular phenotype associated with the p.Y210C mutation. Patients homozygous for the p.R152W mutation presented with a cardiac phenotype, which, despite fulfilling the generally used criteria for attenuated phenotype, may lead to fast disease progression and abrupt death. The knowledge of natural history and genotype–phenotype correlation may help in developing a tailored therapy potentially using enzyme replacement therapy with substrate reduction therapy or chaperones.     

Bovine mucopolysaccharidosis type IIIB

Summary Mucopolysaccharidosis IIIB, an autosomal recessive lysosomal storage disorder of heparan sulfate caused by mutations in the α-N-acetylglucosaminidase (NAGLU) gene, was recently discovered in cattle. Clinical signs include progressive ataxia, stumbling gait, swaying and difficulty in balance and walking. These clinical signs are usually first observed at approximately 2 years of age and then develop progressively over the lifespan of the animals. Affected bulls were found to be homozygous for the missense mutation E452K (c.1354G > A). The availability of mutational analysis permits screening for the NAGLU mutation to eradicate this mutation from the cattle breeding population. Competing interests: None declared References to electronic databases: OMIM disorder/gene accession number: 252920. EC number: 3.2.1.50. HUGO-approved gene symbol: NAGLU. GenBank accession numbers: U43573, P54802, XM_584949.2. The Bovine Genome Project at the Baylor College of Medicine --Baylor bovine genomic nucleotide sequence database: contigs 218996 and 425786.     

Elevated serum biotinidase activity in hepatic glycogen storage disorders–A convenient biomarker

Summary An elevated serum biotinidase activity in patients with glycogen storage disease (GSD) type Ia has been reported previously. The aim of this work was to investigate the specificity of the phenomenon and thus we expanded the study to other types of hepatic GSDs. Serum biotinidase activity was measured in a total of 68 GSD patients and was compared with that of healthy controls (8.7 ± 1.0; range 7.0–10.6 mU/ml; n = 26). We found an increased biotinidase activity in patients with GSD Ia (17.7 ± 3.9; range: 11.4–24.8; n = 21), GSD I non-a (20.9 ± 5.6; range 14.6–26.0; n = 4), GSD III (12.5 ± 3.6; range 7.8–19.1; n = 13), GSD VI (15.4 ± 2.0; range 14.1–17.7; n = 3) and GSD IX (14.0 ± 3.8; range: 7.5–21.6; n = 22). The sensitivity of this test was 100% for patients with GSD Ia, GSD I non-a and GSD VI, 62% for GSD III, and 77% for GSD IX, indicating reduced sensitivity for GSD III and GSD IX, respectively. In addition, we found elevated biotinidase activity in all sera from 5 patients with Fanconi–Bickel Syndrome (15.3 ± 3.7; range 11.0–19.4). Taken together, we propose serum biotinidase as a diagnostic biomarker for hepatic glycogen storage disorders. Competing interests: None declared References to electronic databases: Glycogen storage disease (GSD) Ia: OMIM 232200. GSD I non-a: OMIM 232220. GSD III: OMIM 232400. GSD VI: OMIM 232700. GSD IX: OMIM 306000. Fanconi–Bickel syndrome: OMIM 227810. Cystic fibrosis: OMIM 602421. Gaucher disease: OMIM 230800. Niemann–Pick disease (NP) type A: OMIM 257200. NP type C: OMIM 257220.     

Clinical response to persistent,low-level β-glucuronidase expression in the murine model of mucopolysaccharidosis type VII

Mucopolysaccharidosis type VII (MPS VII) is a lysosomal storage disease caused by β-glucuronidase (GUSB) deficiency. This disease exhibits a broad spectrum of clinical signs including skeletal dysplasia, retinal degeneration, cognitive deficits and hearing impairment. Sustained, high-level expression of GUSB significantly improves the clinical course of the disease in the murine model of MPS VII. Low levels of enzyme expression (1–5% of normal) can significantly reduce the biochemical and histopathological manifestations of MPS VII. However, it has not been clear from previous studies whether persistent, low levels of circulating GUSB lead to significant improvements in the clinical presentation of this disease. We generated a rAAV2 vector that mediates persistent, low-level GUSB expression in the liver. Liver and serum levels of GUSB were maintained at ∼5% and ∼2.5% of normal, respectively, while other tissue ranged from background levels to 0.9%. This level of activity significantly reduced the secondary elevations of α-galactosidase and the levels of glycosaminoglycans in multiple tissues. Interestingly, this level of GUSB was also sufficient to reduce lysosomal storage in neurons in the brain. Although there were small but statistically significant improvements in retinal function, auditory function, skeletal dysplasia, and reproduction in rAAV-treated MPS VII mice, the clinical deficits were still profound and there was no improvement in lifespan. These data suggest that circulating levels of GUSB greater than 2.5% will be required to achieve substantial clinical improvements in MPS VII. Communicating editor: Ed Wraith Competing interests: None declared References to electronic databases: Mucopolysaccharidosis type VII, OMIM +253220; β-glucuronidase, EC 3.2.1.31.     

Effect of ‘attenuated’ mutations in mucopolysaccharidosis IVA on molecular phenotypes of <Emphasis Type="Italic">N</Emphasis>-acetylgalactosamine-6-sulfate sulfatase

Summary Mucopolysaccharidosis IVA is an autosomal recessive disease caused by the deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS). Mutation screening of the GALNS gene was performed for seven MPS IVA patients with attenuated phenotypes from three unrelated families. Four of 5 missense mutations identified in this study (p.F167V, p.R253W, p.R380S, p.P484S) and two reported (p.F97V, p.N204K), associated with attenuated phenotypes, were characterized using in vitro stable expression experiments, enzyme kinetic study, protein processing and structural analysis. The stably expressed mutant enzymes defining the attenuated phenotype exhibited a considerable residual activity (1.2–36.7% of the wild-type GALNS activity) except for p.R380S. Enzyme kinetic studies showed that p.F97V, p.F167V and p.N204K have lower affinity to the substrate compared with other mutants. The p.F97V enzyme was the most thermolabile at 55°C. Immunoblot analyses indicated a rapid degradation and/or an insufficiency in processing in the mutant proteins. Tertiary structure analysis revealed that although there was a tendency for ‘attenuated’ mutant residues to be located on the surface of GALNS, they have a different effect on the protein including modification of the hydrophobic core and salt-bridge formation and different potential energy. This study demonstrates that ‘attenuated’ mutant enzymes are heterogeneous in molecular phenotypes, including biochemical properties and tertiary structure. Competing interests: None declared References to electronic databases: MPS IVA: OMIM #253000. GALNS: EC 3.1.6.4.     

Molecular characterization of Portuguese patients with mucopolysaccharidosis type II shows evidence that the IDS gene is prone to splicing mutations

Summary Mucopolysaccharidosis type II (MPS II) is an X-linked recessive lysosomal storage disease caused by a defect in the iduronate-2-sulfatase gene (IDS). Alternative splicing of the IDS gene can occur and the underlying regulatory mechanism may be rather complex. Nevertheless, little information is available on the role of variations at the IDS locus in the splicing process. Here we report that splice mutations at the IDS locus are an important source of MPS II pathogenicity, accounting for almost 56% of Portuguese cases. Among 16 unrelated Portuguese MPS II patients, 15 different mutations were identified: six intronic splice mutations (c.104−2AG, c.241−2A>G, c.241−1G>A, c.418+1G>A, c.880−8AG and c.1181−1G>C); two exonic splice mutations (c.1006G>lC and c.1122C>T); five missense mutations (D269V, D69V, D148N, R88C and P86L); one nonsense mutation (Q465Ter); one total IDS gene deletion; and one rearrangement involving a IDS gene inversion. Furthermore, nine of the 15 detected mutations affected the usual splicing pattern at the locus. Some of them are responsible for dramatic changes in the splicing mechanism. For example, the substitution mutation, c.418+1G>A, revealed the presence of an exonic sequence inside intron 3. Our study provides evidence that the IDS locus is prone to splicing mutations and that such susceptibility is particularly high in exon 3 and neighbouring regions. Consequently, mutation screening of the IDS gene cannot be restricted to gDNA examination. Unless cDNA analysis is also conducted, misclassifications as silent or missense mutations can be produced and even uncharacteristic splice-site mutations can be misinterpreted as classic splicing defects that may generate severe, unconventional splicing alterations. Communicating editor: Douglas Brooks Competing interests: None declared References to electronic databases. OMIM disorder/gene accession number: 309900. EC number 3.1.6.13. HUGO-approved gene symbol: IDS. GenBank Accession number: AH002847. Vega Gene ID: TTHUMG00000022615. Ensembl Gene ID: ENSG00000010404     

Reduction in bone mineral density in glycogenosis type III may be due to a mixed muscle and bone deficit

Summary  Glycogen storage disease type III (GSD III; OMIM 232400) is an autosomal recessive deficiency of the glycogen debrancher enzyme, amylo-1,6-glucosidase (EC 3.2.1.33). Patients with other hepatic glycogenoses are known to have reduced bone mineral content (BMC) and to be at consequent risk of fractures. They have key metabolic differences from GSD III patients, however. This study examines bone density and metabolism in 15 GSD III patients (6 female) from childhood to adulthood (aged 10–34 years). The results demonstrate that patients with GSD III have low bone mass at all skeletal sites compared with healthy individuals of the same age and sex, with a significant proportion (40–64%) having BMD > 2 standard deviations below the mean for whole body and lumbar spine. The deficiency seems to be attributable to a mixed muscle andbone deficit. Lower bone mass was found at all sites for GSD IIIa patients (combined liver and muscle defect) compared with GSD IIIb patients (liver only defect). Conclusion: Patients with GSD III have significantly abnormal bone mass, placing them at increased risk of potential fracture. The underlying mechanism is probably multifactorial with contributions from abnormal muscle physiology, abnormal metabolic milieu and altered nutrition affecting micronutrient intake. Therapies need to address all these factors to be successful. Competing interests: None declared References to electronic databases: Glycogen storage disease type III: OMIM 232400. Amylo-1,6-glucosidase: EC 3.2.1.33. Glucose-6-phosphatase: EC 3.1.3.9.     

Pathogenesis of CNS involvement in disorders of amino and organic acid metabolism

Summary Inherited disorders of amino and organic acid metabolism have a high cumulative frequency, and despite heterogeneous aetiology and varying clinical presentation, the manifestation of neurological disease is common. It has been demonstrated for some of these diseases that accumulating pathological metabolites are directly involved in the manifestation of neurological disease. Various pathomechanisms have been suggested in different in vitro and in vivo models including an impairment of brain energy metabolism, an imbalance of excitatory and inhibitory neurotransmission, altered transport across the blood–brain barrier and between glial cells and neurons, impairment of myelination and disturbed neuronal efflux of metabolic water. This review summarizes recent knowledge on pathomechanisms involved in phenylketonuria, glutaric aciduria type I, succinic semialdehyde dehydrogenase deficiency and aspartoacylase deficiency with examples, highlighting general as well as disease-specific concepts and their putative impact on treatment. Competing interests: None declared References to electronic databases: Phenylketonuria: OMIM #261600. Glutaric aciduria type I: OMIM #231670. Succinic semialdehyde dehydrogenase deficiency: OMIM #271980. Aspartoacylase disease (Canavan–van Bogaert–Bertrand disease): OMIM #271900. Phenylalanine hydroxylase: EC 1.14.16.1. Glutaryl-CoA dehydrogenase: EC 1.3.99.7. Succinic semialdehyde dehydrogenase: EC 1.2.1.16. Aspartoacylase: EC 3.5.1.15. Presented at the Annual Symposium of the SSIEM, Hamburg, 4–7 September 2007     

Molecular analysis of the GlcNac-1-phosphotransferase

Summary Modification of the carbohydrate chains of soluble lysosomal enzymes with mannose 6-phosphate residues is a prerequisite for their mannose 6-phosphate receptor-dependent transport to lysosomes. GlcNac-1-phosphotransferase localized in the Golgi apparatus represents a hexameric α₂β₂γ₂ subunit complex and plays a key role in the formation of the mannose 6-phosphate recognition marker. Defects in the GlcNac-1-phosphotransferase complex cause two diseases, mucolipidosis type II and III, which are characterized by missorting and cellular loss of lysosomal enzymes, and lysosomal accumulation of storage material. The recent identification of two genes, GNPTAB and GNPTG, encoding the three subunits of GlcNac-1-phosphotransferase leads to an improvement of both pre- and postnatal diagnosis of affected individuals, and permits the analysis of structural requirements for efficient formation of mannose 6-phosphate residues on lysosomal enzymes. The α/β subunits precursor matures by proteolytic cleavage and contains the catalytic activity as well as the capability to recognize lysosomal enzymes. The role of the γ-subunits for activity, stability and oligomerization of the GlcNac-1-phosphotransferase subunits is still unclear. Competing interests: None declared References to electronic databases: Mucolipidosis II and III, OMIM 252500 and 252600. N-Acetyl glucosamine-1-phosphotransferase, EC 2.7.8.1.5. N-Acetyl glucosamine-1-phosphotransferase, EC 2.7.8.15. Presented at the Annual Symposium of the SSIEM, Hamburg, 4–7 September 2007.     

A novel starch for the treatment of glycogen storage diseases

Summary Objective: To determine whether a new starch offers better short-term metabolic control than uncooked cornstarch in patients with glycogen storage diseases (GSDs). Study design: A short-term double-blind cross-over pilot study comparing uncooked physically modified cornstarch (WMHM20) with uncooked cornstarch in patients with GSD types Ia, Ib and III. Twenty-one patients (ages 3–47, 9 female) were given 2 g/kg cornstarch or WMHM20 mixed in water. Blood glucose, lactate and insulin, and breath hydrogen and ¹³CO₂ enrichment were measured, at baseline and after each load. The hourly biochemical evaluations terminated when blood glucose was ≤3.0 mmol/L, when the study period had lasted 10 h or when the patient wished to end the test. The alternative starch was administered under similar trial conditions a median of 10 days later. Results: The median starch load duration was 9 h for WMHM20 versus 7 h for cornstarch. Glucose decreased more slowly (p = 0.05) and lactate was suppressed faster (p = 0.17) for WMHM20 compared with cornstarch. Peak hydrogen excretion was increased (p = 0.05) when cornstarch was taken. Conclusion: These data indicate longer duration of euglycaemia and better short-term metabolic control in the majority of GSD patients with WMHM20 compared to cornstarch. Competing interests: None declared References to electronic databases: Glycogen storage disease I, OMIM 232200. Glycogen storage disease III, OMIM 232400. Glucose-6-phosphatase, EC 3.1.3.9. Amylo-1,6-glucosidase, EC 3.2.1.33. Oligo-1,4–1,4-glucanotransferase, EC 2.4.1.25     

International Morquio A Registry: Clinical manifestation and natural course of Morquio A disease

Summary Mucopolysaccharidosis IVA (MPS IVA; Morquio A disease) is a lysosomal storage disorder caused by deficiency of N-acetylgalactosamine-6-sulfate sulfatase. The natural history of this disease is incompletely understood. To study which variables influence the clinical outcome, we conducted a study in which MPS IVA patients were asked to fill out a questionnaire with inquiries regarding family history, diagnosis, signs and symptoms, height, weight, surgical history, physical activity, and general complaints. A total of 326 patients (172 male, 154 female) from 42 countries enrolled in the Morquio A Registry programme. The mean age of patients enrolled was 14.9 years for males and 19.1 years for females, with a wide range of 1–73 years. Sixty-four per cent of the patients were under 18 years. Initial symptoms were recognized between 1 and 3 years of age (mean age 2.1 years) and mean age at diagnosis for the patients was 4.7 years. A progressive skeletal dysplasia was commonly observed among the MPS IVA patients. Fifty per cent of patients underwent surgical operations to improve their quality of life. The most frequent surgical sites include neck (51%), ear (33%), leg (26%) and hip (25%). The birth length for affected males and females was 52.2 ± 4.7 cm and 52.2 ± 4.5 cm, respectively. The final adult height for affected males and females was 122.5 ± 22.5 cm and 116.5 ± 20.5 cm, respectively. The results of this study provide a reference for assessment of efficacy for studies of novel therapies. Communicating editor: Verena Peters Competing interests: None declared References to electronic databases: MPS IVA, OMIM #253000     

Diagnostic work-up and management of patients with isolated methylmalonic acidurias in European metabolic centres

Summary  The long-term outcome of patients with methylmalonic aciduria (MMA) is still uncertain due to a high frequency of complications such as chronic renal failure and metabolic stroke. The understanding of this disease is hampered by a huge variation in the management of these patients. The major aim of this study was to evaluate the current practice in different European metabolic centres. A standardized questionnaire was sent to 20 metabolic centres asking for standard procedures for confirmation of diagnosis, testing cobalamin responsiveness, dietary treatment, pharmacotherapy, and biochemical and clinical monitoring. Sixteen of 20 metabolic centres (80%) returned questionnaires on 183 patients: 89 of the patients were classified as mut⁰, 36 as mut⁻, 13 as cblA, 7 as cblB, and 38 as cblA/B. (1) Confirmation of diagnosis: All centres investigate enzyme activity by propionate fixation in fibroblasts; six centres also perform mutation analysis. (2) Cobalamin response: Ten centres follow standardized protocols showing large variations. A reliable exclusion of nonspecific effects has not yet been achieved by these protocols. (3) Long-term treatment: In cobalamin-responsive patients, most centres use hydroxocobalamin (1–14 mg/week i.m. or 5–20 mg/week orally), while two centres use cyanocobalamin. All cobalamin-nonresponsive patients and most cobalamin-responsive patients are supplemented with l-carnitine (50–100 mg/kg per day). Fourteen centres use intestinal decontamination by antibiotic therapy. Most centres follow D-A-CH (n = 6) or Dewey (n = 4) recommendations for protein requirements. Fourteen centres regularly use precursor-free amino acid supplements. Standardized monitoring protocols are available in seven centres, again showing high variability. Competing interests: None declared References to electronic databases: Methylmalonic aciduria cblA type: OMIM 251100. Methylmalonic aciduria cblB type: OMIM 251110. Methylmalonic aciduria cblC type: OMIM 277400. Methylmalonic aciduria cblD type: OMIM 277410. Methylmalonic aciduria cblF type: OMIM 277380. Methylmalonic aciduria due to methylmalonyl-CoA mutase deficiency: OMIM 251000. Propionic aciduria: OMIM 606054 Methylmalonyl-CoA mutase: EC 5.4.99.2.     

Effect of Hunter disease (mucopolysaccharidosis type II) mutations on molecular phenotypes of iduronate-2-sulfatase: Enzymatic activity, protein processing and structural analysis

Summary Mucopolysaccharidosis II (Hunter disease), a lysosomal storage disorder caused by a deficiency of iduronate-2-sulfatase (IDS), has variable clinical phenotypes. Nearly 300 different mutations have been identified in the IDS gene from patients with Hunter disease, but the correlation between the genotype and phenotype has remained unclear. We studied the characteristics of 11 missense mutations, which were detected in the patients or artificially introduced, using stable expression experiments and structural analysis. The mutants found in the attenuated phenotype showed considerable residual activity (0.2–2.4% of the wild-type IDS activity) and those in the severe phenotype had no activity. In immunoblot analysis, both the 73–75 kDa precursor and processed forms were detected in the expression of `attenuated' mutants (R48P, A85T and W337R) and the artificial active site mutants (C84S, C84T). The 73–75 kDa initial precursor was detected in the 'severe' mutants (P86L, S333L, S349I, R468Q, R468L). The truncated 68 kDa precursor form was synthesized in the Q531X mutant. The results of immunoblotting indicated rapid degradation and/or insufficiency in processing as a result of structural alteration of the IDS protein. A combination of analyses of genotype and molecular phenotypes, including enzyme activity, protein processing and structural analysis with an engineered reference protein, could provide an avenue to understanding the molecular mechanism of the disease and could give a useful tool for the evaluation of possible therapeutic chemical compounds. Communicating editor: Ed Wraith Competing interests: None declared References to electronic databases: Iduronate-2-sulfatase EC3.1.6.13; mucopolysaccharidoisis II (Hunter disease) OMIM 309900     

The mild form of mucopolysaccharidosis type I (Scheie syndrome) is associated with increased ascending aortic stiffness

Mucopolysaccharidosis type I (MPS IS) is a rare autosomal recessive disease caused by a deficiency of the lysosomal enzyme α-L-iduronidase, which is involved in the degradation of sulfated glycosaminoglycans (GAGs). The deficiency results in the intra-and pericellular accumulation of the GAGs heparan sulfate and dermatan sulfate. Eight adult patients with typical features of MPS IS aged 31.5 ± 6.8 years (five men) were included and compared to age-and gender-matched controls. With transthoracic echocardiography, cyclic ascending aortic diameter changes were measured and ascending aortic elastic properties were calculated to characterize aortic elasticity. In MPS IS patients, aortic stiffness index was significantly increased (23.1 ± 10.4 vs 3.9 ± 1.5, P < 0.001), while aortic distensibility was significantly decreased (1.6 ± 0.8 vs 1.6 ± 1.9 Ca²/dynes 10⁻⁶, P < 0.001) compared to age-and sex-matched controls. The results of the present study demonstrate that in addition to the known cardiac complications, MPS IS patients have an impairment of ascending aortic elasticity. Further follow-up studies are needed to examine arterial elasticity using other methods in this patient population, and to detect possible effects of enzyme replacement therapy.     

Mucopolysaccharidosis type VI: Identification of novel mutations on the arylsulphatase B gene in South American patients

Summary Mucopolysaccharidosis type VI (Maroteaux–Lamy syndrome, MPS VI) is an autosomal recessive disorder caused by deficiency of N-acetylgalactosamine-4-sulphatase (ARSB),which leads to the lysosomal accumulation and excretion of dermatan sulphate (DS). In this study, 13 unrelated MPS VI patients (12 Brazilian and 1 Chilean) were investigated regarding the identification of the ARSB gene mutations using PCR, SSCP and sequencing. The exons with altered mobility on SSCP were sequenced, as well as all the exons of patients with no SSCP alteration. Seven novel mutations were identified: D59N, L72R, Q88H, P93S, R197X, 1279delA and c.1143−8T > G. The previously reported mutations 1533del23, R315Q and 427delG were found in six, three and two alleles respectively. The other mutations already reported, S384N and G144R, were found in only one allele. In addition, three polymorphisms previously described (V358M, V376M and P397P) were detected in the patients analysed. Our findings are in agreement with the literature confirming the great genetic heterogeneity associated with MPS VI.     

Convergent molecular mechanisms underlying cognitive impairment in mucopolysaccharidosis type II

Mucopolysaccharidosis type II (MPS II) is a lysosomal storage disorder caused by pathogenic variants in the iduronate-2-sulfatase gene (IDS), responsible for the degradation of glycosaminoglycans (GAGs) heparan and dermatan sulfate. IDS enzyme deficiency results in the accumulation of GAGs within cells and tissues, including the central nervous system (CNS). The progressive neurological outcome in a representative number of MPSII patients (neuronopathic form) involves cognitive impairment, behavioral difficulties, and regression in developmental milestones. In an attempt to dissect part of the influence of axon guidance instability over the cognitive impairment presentation in MPS II, we used brain expression data, network propagation, and clustering algorithm to prioritize in the human interactome a disease module associated with the MPS II context. We identified new candidate genes and pathways that act in focal adhesion, integrin cell surface, laminin interactions, ECM proteoglycans, cytoskeleton, and phagosome that converge into functional mechanisms involved in early neural circuit formation defects and could indicate clues about cognitive impairment in patients with MPSII. Such molecular changes during neurodevelopment may precede the morphological and clinical evidence, emphasizing the importance of an early diagnosis and directing the development of potential drug leads. Furthermore, our data also support previous hypotheses pointing to shared pathogenic mechanisms in some neurodegenerative diseases.