Capturing phenotypic heterogeneity in MPS I: results of an international consensus procedure

MPSI Manifestations and Treatment Outcome: Skeletal Focus

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

MPS I: Early diagnosis, bone disease and treatment, where are we now?

Mucopolysaccharidosis type I (MPS I) is a lysosomal storage disorder characterized by α-L-iduronidase deficiency. Patients present with a broad spectrum of disease severity ranging from the most severe phenotype (Hurler) with devastating neurocognitive decline, bone disease and early death to intermediate (Hurler-Scheie) and more attenuated (Scheie) phenotypes, with a normal life expectancy. The most severely affected patients are preferably treated with hematopoietic stem cell transplantation, which halts the neurocognitive decline. Patients with more attenuated phenotypes are treated with enzyme replacement therapy. There are several challenges to be met in the treatment of MPS I patients. First, to optimize outcome, early recognition of the disease and clinical phenotype is needed to guide decisions on therapeutic strategies. Second, there is thus far no effective treatment available for MPS I bone disease. The pathophysiological mechanisms behind bone disease are largely unknown, limiting the development of effective therapeutic strategies. This article is a state of the art that comprehensively discusses three of the most urgent open issues in MPS I: early diagnosis of MPS I patients, pathophysiology of MPS I bone disease, and emerging therapeutic strategies for MPS I bone disease.

Ultrasound findings of finger, wrist and knee joints in Mucopolysaccharidosis Type I

INTRODUCTION

Musculoskeletal findings in MPS can progress after enzyme replacement. Our aim was to examine synovial recesses, tendons, retinacula and pulleys using ultrasonography for structural and inflammatory changes.

MATERIAL AND METHODS

The wrist, metacarpophalangeal (MCP), proximal and distal interphalangeal (PIP and DIP) joints, the finger flexor tendons and the knee including entheses of quadriceps and patella tendons were assessed clinically. Ultrasonography of the various synovial recesses of the wrist as well as the extensor retinaculum, carpal tunnel, MCP, PIP and DIP joints of the second finger, extensor and flexor tendons, A1-5 pulleys and the knee joint including relevant entheses followed. Significance of differences between patient values and available normative data were assessed using t-tests.

RESULTS

Ultrasonography showed significant abnormal intraarticular material in the wrist without a clear distribution to synovial recesses and without effusions. Doppler signals were found in a perisynovial distribution and not intrasynovial as expected in in inflammatory arthritis. Findings were similar in the knee but not the fingers. Flexor and extensor tendons were also mostly normal in their structure but significant thickening of retinaculae and the flexor tendon pulleys was seen (p<0.0001 compared to normal).

CONCLUSION

MPS I patients showed intraarticular deposition of abnormal material in the wrist and knee but not in the finger joints where significant thickening of retinaculae/pulleys controlling tendon position was dominant. No ultrasound findings of inflammatory pathology were demonstrated but rather a secondary reaction to abnormal deposition and direct damage of GAG.

Neonatal combination therapy improves some of the clinical manifestations in the Mucopolysaccharidosis type I murine model

Mucopolysaccharidosis type I (MPS-I), a lysosomal storage disorder caused by a deficiency of alpha-L-iduronidase enzyme, results in the progressive accumulation of glycosaminoglycans and consequent multiorgan dysfunction. Despite the effectiveness of hematopoietic stem cell transplantation (HSCT) and enzyme replacement therapy (ERT) in correcting clinical manifestations related to visceral organs, complete improvement of musculoskeletal and neurocognitive defects remains an unmet challenge and provides an impact on patients' quality of life. We tested the therapeutic efficacy of combining HSCT and ERT in the neonatal period. Using a mouse model of MPS-I, we demonstrated that the combination therapy improved clinical manifestations in organs usually refractory to current treatment. Moreover, combination with HSCT prevented the production of anti-IDUA antibodies that negatively impact ERT efficacy. The added benefits of combining both treatments also resulted in a reduction of skeletal anomalies and a trend towards decreased neuroinflammation and metabolic abnormalities. As currently there are limited therapeutic options for MPS-I patients, our findings suggest that the combination of HSCT and ERT during the neonatal period may provide a further step forward in the treatment of this rare disease.

FUNCTIONAL INDEPENDENCE OF PEDIATRIC PATIENTS WITH MUCOPOLYSACCHARIDOSES

OBJECTIVE

To measure the functional independence to perform activities of daily living of pediatric patients diagnosed with mucopolysaccharidoses.

METHODS

A descriptive cross-sectional study was carried out with the population of pediatric patients with a confirmed enzymatic diagnosis of mucopolysaccharidoses, enrolled in the Orthopedics outpatient clinic of a hospital in the State of Bahia. The data were collected between October 2016 and March 2017, based on the documentary analysis of the assessment forms used in the department. The variables of this study comprised sex, age, type of MPS and level of functional independence, measured by the Functional Independence Measure scale.

RESULTS

Twenty-six patients participated in the study. These were predominantly male (61.5%), with a mean age of 10 ± 4.5 years, affected by MPS VI (73.1%). In the motor domain, the mean score was 65 (± 19.9 points); the cognitive domain obtained a mean score equal to 28 (± 8.2 points); and the total FIM score was 93 (± 26.5).

CONCLUSION

Impaired functional independence was observed among children and adolescents with mucopolysaccharidoses. Tasks related to dressing, toileting, bathing, problem solving and social interaction were those that required the most assistance and/or supervision. Level of Evidence IV, Case Series.

GNPTAB c.2404C > T nonsense mutation in a patient with mucolipidosis III alpha/beta: a case report

Background

Mucolipidosis alpha/beta is an inborn error of metabolism characterized by deficiency of GlcNAc-1-phosphotransferase, in which essential alpha/beta subunits are encoded by the GNPTAB gene. The autosomal recessive condition is due to disruptions of hydrolase mannose 6-phosphate marker generation, defective lysosomal targeting and subsequent intracellular accumulation of non-degraded material. Clinical severity depends on residual GlcNAc-1-phosphotransferase activity, which distinguishes between the milder type III disease and the severe, neonatal onset type II disease.

Case presentation

We report the clinical, biochemical and genetic diagnosis of mucolipidosis III alpha/beta in a two-year-old Chinese boy who initially presented with poor weight gain, microcephaly and increased tone. He was confirmed to harbor the common splice site mutation c.2715 + 1G > A and the nonsense variant c.2404C > T (p.Q802*). Clinically, the patient had multiple phenotypic features typical of mucopolysaccharidosis including joint contractures, coarse facial features, kypho-lordosis, pectus carinatum and umbilical hernia. However, the relatively mild developmental delay compared to severe type I and type II mucopolysaccharidosis and the absence of macrocephaly raised the possibility of the less commonly diagnosed mucolipidosis alpha/beta. Critical roles of lysosomal enzyme activity assay, which showed elevated α-iduronidase, iduronate sulfatase, galactose-6-sulphate sulphatase, arylsulfatase B and α-hexosaminidase activities; and genetic study, which confirmed the parental origin of both mutations, were highlighted.

Conclusions

The recently reported nonsense variant c.2404C > T in the GNPTAB gene is further recognized and this contributes to the genotype-phenotype spectrum of mucolipidosis alpha/beta.

Electronic supplementary material

The online version of this article (10.1186/s12881-018-0679-5) contains supplementary material, which is available to authorized users.

Consensus-Based Attributes for Identifying Patients With Spasmodic Dysphonia and Other Voice Disorders

Importance

A roadblock for research on adductor spasmodic dysphonia (ADSD), abductor SD (ABSD), voice tremor (VT), and muscular tension dysphonia (MTD) is the lack of criteria for selecting patients with these disorders.

Objective

To determine the agreement among experts not using standard guidelines to classify patients with ABSD, ADSD, VT, and MTD, and develop expert consensus attributes for classifying patients for research.

Design, Setting and Participants

From 2011 to 2016, a multicenter observational study examined agreement among blinded experts when classifying patients with ADSD, ABSD, VT or MTD (first study). Subsequently, a 4-stage Delphi method study used reiterative stages of review by an expert panel and 46 community experts to develop consensus on attributes to be used for classifying patients with the 4 disorders (second study). The study used a convenience sample of 178 patients clinically diagnosed with ADSD, ABSD, VT MTD, vocal fold paresis/paralysis, psychogenic voice disorders, or hypophonia secondary to Parkinson disease. Participants were aged 18 years or older, without laryngeal structural disease or surgery for ADSD and underwent speech and nasolaryngoscopy video recordings following a standard protocol.

Exposures

Speech and nasolaryngoscopy video recordings following a standard protocol.

Main Outcomes and Measures

Specialists at 4 sites classified 178 patients into 11 categories. Four international experts independently classified 75 patients using the same categories without guidelines after viewing speech and nasolaryngoscopy video recordings. Each member from the 4 sites also classified 50 patients from other sites after viewing video clips of voice/laryngeal tasks. Interrater κ less than 0.40 indicated poor classification agreement among rater pairs and across recruiting sites. Consequently, a Delphi panel of 13 experts identified and ranked speech and laryngeal movement attributes for classifying ADSD, ABSD, VT, and MTD, which were reviewed by 46 community specialists. Based on the median attribute rankings, a final attribute list was created for each disorder.

Results

When classifying patients without guidelines, raters differed in their classification distributions (likelihood ratio, χ2 = 107.66), had poor interrater agreement, and poor agreement with site categories. For 11 categories, the highest agreement was 34%, with no κ values greater than 0.26. In external rater pairs, the highest κ was 0.23 and the highest agreement was 38.5%. Using 6 categories, the highest percent agreement was 73.3% and the highest κ was 0.40. The Delphi method yielded 18 attributes for classifying disorders from speech and nasolaryngoscopic examinations.

Conclusions and Relevance

Specialists without guidelines had poor agreement when classifying patients for research, leading to a Delphi-based development of the Spasmodic Dysphonia Attributes Inventory for classifying patients with ADSD, ABSD, VT, and MTD for research.

Phenotype prediction for mucopolysaccharidosis type I by in silico analysis

BACKGROUND

Mucopolysaccharidosis type I (MPS I) is an autosomal recessive disease due to deficiency of α-L-iduronidase (IDUA), a lysosomal enzyme that degrades glycosaminoglycans (GAG) heparan and dermatan sulfate. To achieve optimal clinical outcomes, early and proper treatment is essential, which requires early diagnosis and phenotype severity prediction.

RESULTS

To establish a genotype/phenotype correlation of MPS I disease, a combination of bioinformatics tools including SIFT, PolyPhen, I-Mutant, PROVEAN, PANTHER, SNPs&GO and PHD-SNP are utilized. Through analyzing single nucleotide polymorphisms (SNPs) by these in silico approaches, 28 out of 285 missense SNPs were predicted to be damaging. By integrating outcomes from these in silico approaches, a prediction algorithm (sensitivity 94%, specificity 80%) was thereby developed. Three dimensional structural analysis of 5 candidate SNPs (P533R, P496R, L346R, D349G, T374P) were performed by SWISS PDB viewer, which revealed specific structural changes responsible for the functional impacts of these SNPs. Additionally, SNPs in the untranslated region were analyzed by UTRscan and PolymiRTS. Moreover, by investigating known pathogenic mutations and relevant patient phenotypes in previous publications, phenotype severity (severe, intermediate or mild) of each mutation was deduced.

CONCLUSIONS

Collectively, these results identified potential candidate SNPs with functional significance for studying MPS I disease. This study also demonstrates the effectiveness, reliability and simplicity of these in silico approaches in addressing complexity of underlying genetic basis of MPS I disease. Further, a step-by-step guideline for phenotype prediction of MPS I disease is established, which can be broadly applied in other lysosomal diseases or genetic disorders.

Novel frameshift variant in the IDUA gene underlies Mucopolysaccharidoses type I in a consanguineous Yemeni pedigree

Mucopolysaccharidosis type I (MPS I) is an autosomal recessive storage disorder that result as a consequence of a deficiency in the lysosomal hydrolase, a-L-iduronidase enzyme encoded by IDUA gene. Over a hundred causative variants in IDUA have been identified, which result in a progressive multi-systemic disease with a broad range of severity and disease progression reported across affected individuals. The aim of this study was the detection and interpretation of IDUA mutation in a family with two children affected with lethal MPS I. The IDUA gene was sequenced in the parents of two deceased children who had a clinical diagnosis of MPS I, to assess their carrier status and to help inform on risk in future children. The sequencing analysis was performed by PCR and bidirectional Sanger sequencing of the coding region and exon-intron splice junctions at Labor MVZ Westmecklenburg molecular diagnostics laboratory. A heterozygous c.657delA variant in exon 6 was identified in each parent, which is the most likely explanation for disease in their children. This report represents the first Yemeni family to have a molecular diagnosis for MPS I.

Musculoskeletal manifestations in mucopolysaccharidosis type I (Hurler syndrome) following hematopoietic stem cell transplantation

BACKGROUND

Hematopoietic stem cell transplantation (HSCT) is the treatment of choice for young Hurler patients. Despite halting of neurocognitive decline and improvement of life expectancy, the beneficial effect on the skeletal system is limited. As orthopedic complications are one of the most disabling factors following HSCT, this points to the need for new treatment strategies. The study summarizes musculoskeletal manifestations in 19 transplanted Hurler patients.

METHODS

Data were obtained retrospectively. Patients' charts for physical examinations of the joint range of motion (JROM) of shoulders, elbows, hips and knees were reviewed. Radiographic evaluations of thorax, spine, pelvis and hands were performed. MRI scans of the craniocervical junction were analyzed to determine odontoid hypoplasia and the prevalence of craniocervical stenosis.

RESULTS

Nineteen Hurler patients (10 females, 9 males) with an average age of 8.1 years (range 2.5-23.8) at the latest follow-up, who underwent allogenic HSCT between 1991 and 2012, were assessed after an average follow-up period of 6.4 years (range 0.7-22.5). Seventeen patients achieved long-term engraftment, two developed graft failures. The majority of patients showed a steady state or improvements in the mobility of knees (31 %/63 %), hips (47 %/40 %) and elbows (56 %/38 %). However, shoulder abduction was impaired in ¾ of patients and showed the highest rate of progression (31 %). In patients with graft failure, progressive restrictions in JROM were noted. Assessments of the craniocervical junction by MRI showed stable or improved diameters in 67 % of patients. Correction or stabilization of odontoid hypoplasia was found in 64 %. However thoracolumbar kyphosis, scoliosis, hip dysplasia and genua valga were progressive despite HSCT. At the last follow up, 47 % of patients were partially wheelchair dependent, 10 % wheelchair bound and 25 % regularly experienced pain in the spine, hips and lower extremities due to orthopedic problems.

CONCLUSION

Joint mobility, odontoid hypoplasia and craniocervical stenosis might stabilize or even improve in Hurler patients following HSCT. However, despite the beneficial effects on some musculoskeletal manifestations, skeletal complications are frequently observed and the overall burden of orthopedic disease is significant. Frequent multi-disciplinary follow-up in a specialized center are essential. Novel therapeutic approaches (e.g. anti-inflammatory drugs) are needed to improve musculoskeletal outcomes.

Review and evaluation of the methodological quality of the existing guidelines and recommendations for inherited neurometabolic disorders

BACKGROUND

Inherited neurometabolic disorders (iNMDs) represent a group of almost seven hundred rare diseases whose common manifestations are clinical neurologic or cognitive symptoms that can appear at any time, in the first months/years of age or even later in adulthood. Early diagnosis and timely treatments are often pivotal for the favorable course of the disease. Thus, the elaboration of new evidence-based recommendations for iNMD diagnosis and management is increasingly requested by health care professionals and patients, even though the methodological quality of existing guidelines is largely unclear. InNerMeD-I-Network is the first European network on iNMDs that was created with the aim of sharing and increasing validated information about diagnosis and management of neurometabolic disorders. One of the goals of the project was to determine the number and the methodological quality of existing guidelines and recommendations for iNMDs.

METHODS

We performed a systematic search on PubMed, the National Guideline Clearinghouse (NGC), the Guidelines International Network (G-I-N), the Scottish Intercollegiate Guideline Network (SIGN) and the National Institute for Health and Care Excellence (NICE) to identify all the published guidelines and recommendations for iNMDs from January 2000 to June 2015. The methodological quality of the selected documents was determined using the AGREE II instrument, an appraisal tool composed of 6 domains covering 23 key items.

RESULTS

A total of 55 records met the inclusion criteria, 11 % were about groups of disorders, whereas the majority encompassed only one disorder. Lysosomal disorders, and in particular Fabry, Gaucher disease and mucopolysaccharidoses where the most studied. The overall methodological quality of the recommendation was acceptable and increased over time, with 25 % of the identified guidelines strongly recommended by the appraisers, 64 % recommended, and 11 % not recommended. However, heterogeneity in the obtained scores for each domain was observed among documents covering different groups of disorders and some domains like 'stakeholder involvement' and 'applicability' were generally scarcely addressed.

CONCLUSIONS

Greater efforts should be devoted to improve the methodological quality of guidelines and recommendations for iNMDs and AGREE II instrument seems advisable for new guideline development. The elaboration of new guidelines encompassing still uncovered disorders is badly needed.

[Mucopolysaccharidosis: clinical features, diagnosis and management]

The mucopolysaccharidoses (MPS) are a group of rare (orphan) diseases, characterised by a deficiency of enzymes involved in the metabolism of glycosaminoglycans (GAGs) at lysosomal level. When there is a deficiency of a particular enzyme there is an accumulation of GAGs in the cells resulting in progressive cellular damage, which can affect multiple organ systems and lead to organ failure. Diagnosis is based on knowledge of the clinical manifestations, performing biochemical analyses to identify the type of GAG that is accumulating, and confirm the type of disorder with the corresponding enzymatic determination. Their identification is essential to initiate early treatment, taking into account that multidisciplinary management and enzyme replacement therapy is available for MPS I (Hurler syndrome), MPS II (Hunter syndrome), MPS IV (Morquio syndrome), and MPS VI (Maroteaux-Lamy syndrome. In this review, an analysis is made of each of these syndromes, as well as their diagnosis and treatment.

Effects of enzyme replacement therapy started late in a murine model of mucopolysaccharidosis type I

Mucopolysaccharidosis type I (MPS I) is a progressive disorder caused by deficiency of α-L-iduronidase (IDUA), which leads to storage of heparan and dermatan sulphate. It is suggested that early enzyme replacement therapy (ERT) leads to better outcomes, although many patients are diagnosed late and don’t receive immediate treatment. This study aims to evaluate the effects of late onset ERT in a MPS I murine model. MPS I mice received treatment from 6 to 8 months of age (ERT 6–8mo) with 1.2mg laronidase/kg every 2 weeks and were compared to 8 months-old wild-type (Normal) and untreated animals (MPS I). ERT was effective in reducing urinary and visceral GAG to normal levels. Heart GAG levels and left ventricular (LV) shortening fraction were normalized but cardiac function was not completely improved. While no significant improvements were found on aortic wall width, treatment was able to significantly reduce heart valves thickening. High variability was found in behavior tests, with treated animals presenting intermediate results between normal and affected mice, without correlation with cerebral cortex GAG levels. Cathepsin D activity in cerebral cortex also did not correlate with behavior heterogeneity. All treated animals developed anti-laronidase antibodies but no correlation was found with any parameters analyzed. However, intermediary results from locomotion parameters analyzed are in accordance with intermediary levels of heart function, cathepsin D, activated glia and reduction of TNF-α expression in the cerebral cortex. In conclusion, even if started late, ERT can have beneficial effects on many aspects of the disease and should be considered whenever possible.

Long-term outcome of Hurler syndrome patients after hematopoietic cell transplantation: an international multicenter study

Mucopolysaccharidosis type I-Hurler syndrome (MPS-IH) is a lysosomal storage disease characterized by multisystem morbidity and death in early childhood. Although hematopoietic cell transplantation (HCT) has been performed in these patients for more than 30 years, large studies on the long-term outcome of patients with MPS-IH after HCT are lacking. The goal of this international study was to identify predictors of the long-term outcome of patients with MPS-IH after successful HCT. Two hundred seventeen patients with MPS-IH successfully engrafted with a median follow-up age of 9.2 years were included in this retrospective analysis. Primary endpoints were neurodevelopmental outcomes and growth. Secondary endpoints included neurologic, orthopedic, cardiac, respiratory, ophthalmologic, audiologic, and endocrinologic outcomes. Considerable residual disease burden was observed in the majority of the transplanted patients with MPS-IH, with high variability between patients. Preservation of cognitive function at HCT and a younger age at transplantation were major predictors for superior cognitive development posttransplant. A normal α-l-iduronidase enzyme level obtained post-HCT was another highly significant predictor for superior long-term outcome in most organ systems. The long-term prognosis of patients with MPS-IH receiving HCT can be improved by reducing the age at HCT through earlier diagnosis, as well as using exclusively noncarrier donors and achieving complete donor chimerism.

[Hurler syndrome: early diagnosis and treatment]

Hurler syndrome, the most severe form of mucopolysaccharidosis type I (MPS I), is a rare lysosomal storage disease. The overall incidence of MPS I is 0.99-1.99/100,000 live births. Accumulation of glycosaminoglycans causes the progressive dysfunction of multiple organs. We report the case of a 3-week-old newborn who was hospitalized in the Neonatal Intensive Care Unit for feeding problems. Coarse facial features and gingival hypertrophy, associated with axial hypotonia, upper airway obstruction, and moderate hepatomegaly, led to the early diagnosis of MPS I at 3 weeks of age and was confirmed by an abnormally elevated amount of dermatan and heparan sulphate in the urine and complete deficiency of alpha-L-iduronidase lysosomal enzyme activity. The child was homozygous for the p.W402X mutation, located on chromosome 4p16.3 of the alpha-L-iduronidase (IDUA) gene. The clinical condition gradually deteriorated until the age of 4 months, with thoracic and lumbar dysostoses, glaucoma, cerebral ventricular dilatation and cervical spinal stenosis, dilated cardiomyopathy, and umbilical hernia. Early diagnosis allowed enzyme replacement therapy (iaronidase, Aldurazyme(®), Genzyme) started at the age of 5 months, which provided stabilization of the heart disease, significant regression of rhinologic symptoms, and regression of hepatomegaly. Cord blood hematopoietic stem cell transplantation was performed at 11 months of age, allowing optimal preservation of cognitive development.

Isokinetic muscle strength differences in patients with mucopolysaccharidosis I, II, and VI

PURPOSE

To determine muscular strength differences in patients with MPS-I, II, and VI versus age- and sex-matched healthy controls.

METHODS

Dominant leg isokinetic knee extension strength was measured at 90 and 120 degrees per second (d/s) using a dynamometer in 30 subjects with MPS and 42 controls (5-16 yrs). MPS-I was further divided into MPS-IA (attenuated) and MPS-IH (severe). Strength measures analyzed were peak torque (PkT), peak torque per unit body weight (PkT/BW) and per unit lean body mass (PkT/LBM), and average power (AP).

RESULTS

Following adjusting strength measures for age, MPS-IH and MPS-II had significantly lower strength measures for all variables at both angular velocities. MPS-VI had significantly lower PkT, PkT/LBM, and AP compared to controls at 90 and 120d/s. In contrast, MPS-IA was not significantly different from controls for any strength variable at either angular velocity.

CONCLUSION

The results of this study suggest that decrements in skeletal muscle strength depend on MPS diagnosis and severity of disease. Children with MPS-IH demonstrate the greatest difference in muscular strength compared to healthy controls.

Osteoimmunology in mucopolysaccharidoses type I, II, VI and VII. Immunological regulation of the osteoarticular system in the course of metabolic inflammation

BACKGROUND

Mucopolysaccharidoses (MPSs) are rare genetic diseases caused by a deficient activity of one of the lysosomal enzymes involved in the glycosaminoglycan (GAG) breakdown pathway. These metabolic blocks lead to the accumulation of GAGs in various organs and tissues, resulting in a multisystemic clinical picture. The pathological GAG accumulation begins a cascade of interrelated responses: metabolic, inflammatory and immunological with systemic effects. Metabolic inflammation, secondary to GAG storage, is a significant cause of osteoarticular symptoms in MPS disorders.

OBJECTIVE AND METHOD

The aim of this review is to present recent progress in the understanding of the role of inflammatory and immune processes in the pathophysiology of osteoarticular symptoms in MPS disorders and potential therapeutic interventions based on published reports in MPS patients and studies in animal models.

RESULTS AND CONCLUSIONS

The immune and skeletal systems have a number of shared regulatory molecules and many relationships between bone disorders and aberrant immune responses in MPS can be explained by osteoimmunology. The treatment options currently available are not sufficiently effective in the prevention, inhibition and treatment of osteoarticular symptoms in MPS disease. A lot can be learnt from interactions between skeletal and immune systems in autoimmune diseases such as rheumatoid arthritis (RA) and similarities between RA and MPS point to the possibility of using the experience with RA in the treatment of MPS in the future. The use of different anti-inflammatory drugs requires further study, but it seems to be an important direction for new therapeutic options for MPS patients.

Mucopolysaccharidoses and other lysosomal storage diseases

Mucopolysaccharidosis and other lysosomal storage diseases are rare, chronic, and progressive inherited diseases caused by a deficit of lysosomal enzymes. Patients are affected by a wide variety of symptoms. For some lysosomal storage diseases, effective treatments to arrest disease progression, or slow the pathologic process, and increase patient life expectancy are available or being developed. Timely diagnosis is crucial. Rheumatologists, orthopedics, and neurologists are commonly consulted due to unspecific musculoskeletal signs and symptoms. Pain, stiffness, contractures of joints in absence of clinical signs of inflammation, bone pain or abnormalities, osteopenia, osteonecrosis, secondary osteoarthritis or hip dysplasia are the alerting symptoms that should induce suspicion of a lysosomal storage disease.

An algorithm to predict phenotypic severity in mucopolysaccharidosis type I in the first month of life

Introduction

Mucopolysaccharidosis type I (MPS I) is a progressive multisystem lysosomal storage disease caused by deficiency of the enzyme α-L-iduronidase (IDUA). Patients present with a continuous spectrum of disease severity, and the most severely affected patients (Hurler phenotype; MPS I-H) develop progressive cognitive impairment. The treatment of choice for MPS I-H patients is haematopoietic stem cell transplantation, while patients with the more attenuated phenotypes benefit from enzyme replacement therapy.

The potential of newborn screening (NBS) for MPS I is currently studied in many countries. NBS for MPS I, however, necessitates early assessment of the phenotype, in order to decide on the appropriate treatment. In this study, we developed an algorithm to predict phenotypic severity in newborn MPS I patients.

Methods

Thirty patients were included in this study. Genotypes were collected from all patients and all patients were phenotypically categorized at an age of > 18 months based on the clinical course of the disease. In 18 patients, IDUA activity in fibroblast cultures was measured using an optimized IDUA assay. Clinical characteristics from the first month of life were collected from 23 patients.

Results

Homozygosity or compound heterozygosity for specific mutations which are associated with MPS I-H, discriminated a subset of patients with MPS I-H from patients with more attenuated phenotypes (specificity 100%, sensitivity 82%). Next, we found that enzymatic analysis of IDUA activity in fibroblasts allowed identification of patients affected by MPS I-H. Therefore, residual IDUA activity in fibroblasts was introduced as second step in the algorithm. Patients with an IDUA activity of < 0.32 nmol x mg^-1 × hr^-1 invariably were MPS I-H patients, while an IDUA activity of > 0.66 nmol × mg^-1 × hr^-1 was only observed in more attenuated patients. Patients with an intermediate IDUA activity could be further classified by the presence of differentiating clinical characteristics, resulting in a model with 100% sensitivity and specificity for this cohort of patients.

Conclusion

Using genetic, biochemical and clinical characteristics, all potentially available in the newborn period, an algorithm was developed to predict the MPS I phenotype, allowing timely initiation of the optimal treatment strategy after introduction of NBS.

Delphi approach to select rare diseases for a European representative survey. The BURQOL-RD study

OBJECTIVES

The BURQOL-RD project is intended to develop a disease based model capable of quantifying the socio-economic burden and health-related quality of life for patients with rare diseases (RDs) and their caregivers in Europe. We described the methodology used to select a set of 10 RDs to be approached in a pilot study.

METHODS

BURQOL-RD project includes 23 partners from 8 European countries: Spain, UK, France, Germany, Sweden, Italy, Hungary and Bulgaria. A two-round Delphi panels in combination with Carroll diagram was used to generate consensus in the selection of the 10 RDs among the project participants.

RESULTS

The two Delphi rounds yielded a prioritised list, to which the Carroll diagram was applied, taking into account three determinants: prevalence, availability of effective treatment and need for carer. The final set of RD to be studied was obtained: cystic fibrosis, Prader-Willi syndrome, haemophilia, duchenne muscular dystrophy, epidermolysis bullosa, fragile X syndrome, scleroderma, mucopolysaccharidosis, juvenile idiopathic arthritis and histiocytosis.

CONCLUSIONS

This methodology permitted the generation of an equilibrated set of RDs for the pilot study of BURQOL-RD project. The model will be suitable for application in a wide range of RDs.