The pathophysiology of GD - current understanding and rationale for existing and emerging therapeutic approaches

Gaucher disease is a genetic disorder of sphingolipid metabolism resulting from dysfunction of the lysosomal membrane-associated glycoprotein glucocerebrosidase (GBA) and resulting in intracellular accumulation of glucosylceramide and other glycolipids. Although the gene defect and relevant biochemical pathways have been defined, the mechanisms by which substrate accumulation causes disease manifestations are not well understood. The direct effects of a build up of substrate laden cells may account for some aspects of disease but the overall pathology is likely to be more complex with effects of stored material on a variety of intra and extra cellular functions. In this article we review the GBA gene and its protein product, with associated defects, lipid metabolism and storage, enzyme misfolding and endoplasmic reticulum stress, calcium homeostasis, oxidative stress and autophagy and at each point examine how therapies that are currently available, in clinical development or at earlier stages of basic research might address the pathological mechanisms.

Evaluation of high density lipoprotein as a circulating biomarker of Gaucher disease activity

Circulating biomarkers are important surrogates for monitoring disease activity in type I Gaucher disease (GD1). We and others have reported low high-density lipoprotein (HDL) in GD1. We assessed HDL cholesterol as a biomarker of GD1, with respect to its correlation with indicators of disease severity and its response to imiglucerase enzyme replacement therapy (ERT). In 278 consecutively evaluated GD1 patients, we correlated HDL cholesterol, chitotriosidase, and angiotensin-converting enzyme (ACE) with indicators of disease severity. Additionally, we measured the response of these biomarkers to ERT. HDL cholesterol was negatively correlated with spleen volume, liver volume, and GD severity score index; the magnitude of this association of disease severity with HDL cholesterol was similar to that for ACE and for chitotriosidase. Within individual patients monitored over many years, there was a strikingly strong correlation of HDL with liver and spleen volumes; there was a similarly strong correlation of chitotriosidase and ACE with disease severity in individual patients monitored serially over many years (chitotriosidase r = 0.96 to 0.98, ACE r = 0.88 to 0.94, and HDL r = -0.84 to -0.94, p < 0.001). ERT for 3 years resulted in a striking increase of HDL while serum levels of chitotriosidase and ACE decreased. Our results reveal markedly low HDL cholesterol in untreated GD1, a correlation with indicators of disease severity in GD1, and a rise towards normal after ERT. These findings suggest HDL cholesterol merits inclusion within the "biomarker basket" for monitoring of patients with GD1.

Velaglucerase alfa as a therapeutic option for Gaucher disease

Gaucher disease (GD) is an inherited disorder characterized by deficiency of the lysosomal enzyme glucocerebrosidase and the accumulation of an incompletely metabolized substrate (glucocerebroside) in cells of monocyte lineage. Clinical manifestations include anemia, thrombocytopenia, hepatosplenomegaly and bone disease; in a subset of patients with the neuropathic form, additional problems related to primary CNS involvement develop, resulting in a shortened lifespan. Velaglucerase alfa is a human recombinant formulation of glucocerebrosidase; in clinical trials it has been shown to be safe and effective in reversing the cardinal systemic features of GD. Prior to the introduction of velaglucerase alfa, enzyme replacement therapy with imiglucerase for GD type 1 (the non-neuronopathic form) had been established as the standard of care. Problems with imiglucerase supply have resulted in the increased use of velaglucerase alfa, through an expanded access program prior to regulatory approval (which was obtained in February 2010 in the USA and more recently in countries of the EU). Thus far, the therapeutic profile for velaglucerase alfa appears comparable to the historical data set for imiglucerase, although the reported rate of antibody formation against velaglucerase alfa is lower (1 vs 15%). In addition, in vitrostudies involving human macrophages have demonstrated a more rapid internalization of velaglucerase alfa. The long-term implications of these observations need to be established. Moreover, factors that will influence the choice of treatment agent in GD patients will need to be determined.

Focal splenic lesions in type I Gaucher disease are associated with poor platelet and splenic response to macrophage-targeted enzyme replacement therapy

Focal splenic lesions (FSL) occur in Gaucher disease type I (GD1), but their clinical significance is not known. Previous studies estimated the prevalence of FSL at 4% (pediatric) to 33% (adult) of GD1 patients and reported an association with splenomegaly. We tested the hypothesis that the presence of FSL is associated with suboptimal response to macrophage-directed enzyme replacement therapy (ERT). Additionally we investigated whether FSL were associated with other phenotypic features of GD1. The splenic parenchyma was assessed by MRI performed for routine evaluation of GD1 in 239 consecutive GD1 patients with intact spleens. The prevalence of FSL was 18.4% (44/239). Following a mean of 3.5 years of ERT, platelet response was inferior among patients with FSL (80,700 ± 9,600 to 90,100 ± 7,200/mm(3) , P = 0.2) compared to patients without FSL in whom there was a robust platelet response: 108,600 ± 5,670 to 150,200 ± 6,710/mm(3), P < 0.001. Compared to patients without FSL, patients harboring FSL had worse thrombocytopenia (platelet count: 83,700 ± 8,800 vs. 112,100 ± 4,200/mm(3), P = 0.004), greater frequency of pre-ERT splenomegaly, and greater post-ERT splenomegaly (8.5 ± 0.77 vs. 4.8 ± 0.25× normal, P < 0.001). Additionally, the prevalence of osteonecrosis was higher among patients with FSL compared to patients without FSL (38 vs. 20.7%, P = 0.026). FSL appear to be a determinant of response to ERT, suggesting studies comparing relative efficacy of newly emerging therapies for GD1 should adjust for this factor. Moreover, occurrences of FSL coincide with more severe manifestations of GD1 such as avascular osteonecrosis.

Long-term outcomes of liver transplantation in type 1 Gaucher disease

Gaucher disease (GD) is the most prevalent lysosomal storage disorder. Enzyme replacement therapy (ERT) has demonstrable efficacy in reversing clinical and pathological manifestations of GD. We report four patients with GD and severe hepatic impairment who were successfully treated by orthotopic liver transplantation. Liver failure resulted from GD in two patients and due to a comorbidity in two others (HCV and autoimmune chronic active hepatitis). Following successful liver transplantation, patients received long-term ERT. Liver transplantation is a life-saving treatment for end-stage liver disease in patients with Gaucher disease. All four patients have had excellent outcomes from liver transplantation for up to 10 years postprocedure with no evidence of Gaucher-related pathology in the graft.

Therapeutic approaches for lysosomal storage diseases

The lysosomal storage disorders (LSDs) comprise a heterogeneous group of inborn errors of metabolism characterized by tissue substrate deposits, most often caused by a deficiency of the enzyme normally responsible for catabolism of various byproducts of cellular turnover. Individual entities are typified by involvement of multiple body organs, in a pattern reflecting the sites of substrate storage. It is increasingly recognized that one or more processes, such as aberrant inflammation, dysregulation of apoptosis and/or defects of autophagy, may mediate organ dysfunction or failure. Several therapeutic options for various LSDs have been introduced, including hematopoietic stem cell transplantation, enzyme replacement therapy and substrate reduction therapy. Additional strategies are being explored, including the use of pharmacological chaperones and gene therapy. Most LSDs include a variant characterized by primary central nervous system (CNS) involvement. At present, therapy of the CNS manifestations remains a major challenge because of the inability to deliver therapeutic agents across the intact blood-brain barrier. With improved understanding of underlying disease mechanisms, additional therapeutic options may be developed, complemented by various strategies to deliver the therapeutic agent(s) to recalcitrant sites of pathology such as brain, bones and lungs.

Enzyme replacement therapy for Anderson-Fabry disease

BACKGROUND

Anderson-Fabry disease is an X-linked defect of glycosphingolipid metabolism. Progressive renal insufficiency is a major source of morbidity, additional complications result from cardio- and cerebro-vascular involvement. Survival is reduced among affected males and symptomatic female carriers.

OBJECTIVES

To evaluate the effectiveness and safety of enzyme replacement therapy compared to other interventions, placebo or no interventions, for treating Anderson-Fabry disease.

SEARCH STRATEGY

We searched 'Clinical Trials' on The Cochrane Library, MEDLINE, EMBASE, LILACS and the Cystic Fibrosis and Genetic Disorders Group's Inborn Errors of Metabolism Trials Register (date of the most recent search: 07 April 2010).

SELECTION CRITERIA

Randomized controlled trials of agalsidase alfa or beta in participants diagnosed with Anderson-Fabry disease.

DATA COLLECTION AND ANALYSIS

Two authors selected relevant trials, assessed methodological quality and extracted data.

MAIN RESULTS

Five studies comparing either agalsidase alfa or beta in 187 participants fulfilled the selection criteria.Both trials comparing agalsidase alfa to placebo reported on globotriaosylceramide concentration in plasma and tissue; aggregate results were non-significant. One study reported pain scores, there was a statistically significant improvement for participants receiving treatment at up to three months, mean difference -2.10 (95% confidence interval (CI) -3.79 to -0.41); at up to five months, mean difference -1.90 (95% CI -3.65 to -0.15); and at up to six months, mean difference -2.00 (95% CI -3.66 to -0.34). There was a significant difference in pain-related quality of life at over five months and up to six months, mean difference -2.10 (95% CI -3.92 to -0.28) but not at other time-points. Neither study reported deaths.One of the three trials comparing agalsidase beta to placebo reported on globotriaosylceramide concentration in plasma and tissue and showed significant improvement: kidney, mean difference -1.70 (95% CI -2.09 to -1.31); heart, mean difference -0.90 (95% CI -1.18 to -0.62); and composite results (renal, cardiac, and cerebrovascular complications and death), mean difference -4.80 (95% CI -5.45 to -4.15). There was no significant difference between groups for death; no studies reported on pain.

AUTHORS' CONCLUSIONS

Five small, poor quality randomised controlled trials provide no robust evidence for use of either agalsidase alfa and beta to treat Anderson-Fabry disease.

Expanding spectrum of the association between Type 1 Gaucher disease and cancers: a series of patients with up to 3 sequential cancers of multiple types--correlation with genotype and phenotype

In Gaucher disease (GD), inherited deficiency of lysosomal glucocerebrosidase due to mutations in GBA1 gene results in accumulation of glucosylceramide in tissue macrophages, systemic macrophage activation, and a complex multisystemic phenotype. We and others have reported an increased risk of multiple myeloma and other malignancies in non-neuronopathic Type 1 GD (GD1). Here, we describe a subset of GD1 patients with multiple malignancies. In our cohort of 403 patients with GD1, nine patients (2.2%) developed two or three different types of cancers either consecutively or simultaneously. Patients were characterized by age at diagnosis of GD1, GBA1 genotype, disease severity, age at cancer diagnosis, enzyme replacement therapy (ERT) status, and splenectomy status. Of the nine patients, six developed two types of malignancies and three had three cancers each. Overall, the hematologic malignancies comprised lymphoma/leukemia (4) and multiple myeloma (4). Nonhematologic malignancies included colon (2), lung (2), thyroid (2), and prostate cancer (1). Of the seven patients who received ERT, the first cancer was diagnosed before initiation of ERT in all but one. Asplenic patients were more likely to have single or multiple cancers compared with patients with intact spleens (P < 0.0072 and P < 0.0203, respectively). Our data strengthen the association of GD1 and cancer and suggest that patients may be at risk of developing multiple malignancies. We found an association between splenectomy and multiple cancers in GD1. It will be of interest to determine whether timely ERT and declining rates of splenectomy will translate into declining rates of multiple and single cancers.

Leukoencephalopathies and leukodystrophies

The leukoencephalopathies encompass a heterogeneous group of disorders that involve the brain white matter. The cause may be acquired or inherited; in the latter case, mutations have been found in genes that encode protein components of the myelin membrane or enzymes implicated in the turnover of myelin. In patients with cognitive dysfunction and white matter lesions evident on MRI, analysis of the type, pattern, and distribution of lesions can enable a presumptive diagnosis, which can be confirmed by biochemical and/or molecular testing. The presence or absence of peripheral neuropathy and/or autonomic dysfunction can be a helpful clue in differentiating individual diagnoses. Often, patients may be suspected of having and being initially treated inappropriately for a case of primary or secondary progressive multiple sclerosis. In a significant number of patients, the diagnosis may not be made, even after an extensive search. Establishing the cause enables counseling regarding prognosis, family planning, monitoring for disease-related complications, and introducing therapy, when available.

Velaglucerase alfa, a human recombinant glucocerebrosidase enzyme replacement therapy for type 1 Gaucher disease

Gaucher disease (GD) is caused by a deficiency of the lysosomal enzyme glucocerebrosidase, which results in the accumulation of its substrate, glucocerebroside, in macrophages. This excess in lipid storage within macrophages (subsequently recognized as Gaucher cells) leads to the development of disease, which presents clinical features including anemia, thrombocytopenia and hepatosplenomegaly, and can also lead to the development of neurological problems or bone disease. Velaglucerase alfa is a gene-activated human recombinant glucocerebrosidase being developed by Shire Human Genetic Therapies Inc as an enzyme replacement therapy for type 1 GD. In vitro, velaglucerase alfa was internalized by human macrophages more rapidly than imiglucerase, which has been the sole standard of care for GD for over 15 years. Clinical trials in patients with GD demonstrated that the safety and efficacy of velaglucerase alfa appeared to be comparable with historical imiglucerase data, although head-to-head data were unavailable. Recent problems with the production of imiglucerase led to the unanticipated introduction of velaglucerase alfa to patients with GD through a pre-approval expanded access protocol. Whether this will prove beneficial, in terms of uptake and prescribing of the enzyme, remains to be seen in a market dominated by imiglucerase.

Joint contractures in the absence of inflammation may indicate mucopolysaccharidosis

BACKGROUND

Undiagnosed patients with the attenuated form of mucopolysaccharidosis (MPS) type I often have joint symptoms in childhood that prompt referral to a rheumatologist. A survey conducted by Genzyme Corporation of 60 European and Canadian rheumatologists and pediatric rheumatologists demonstrated that < 20% recognized signs and symptoms of MPS I or could identify appropriate diagnosis tests. These results prompted formation of an international working group of rheumatologists, pediatric rheumatologists, and experts on MPS I to formulate a rheumatology-based diagnostic algorithm. The resulting algorithm applies to all MPS disorders with musculoskeletal manifestations.Bone and joint manifestations are prominent among most patients with MPS disorders. These life-threatening lysosomal storage diseases are caused by deficient activity of specific enzymes involved in the degradation of glycosaminoglycans. Patients with attenuated MPS disease often experience diagnostic delays. Enzyme replacement therapy is now commercially available for MPS I (laronidase), MPS II (idursulfase), and MPS VI (galsulfase).

PRESENTATION OF THE HYPOTHESIS

Evolving joint pain and joint contractures in the absence of inflammation should always raise the suspicion of an MPS disorder. All such patients should undergo urinary glycosaminoglycan (uGAG) analysis (not spot tests for screening) in a reputable laboratory. Elevated uGAG levels and/or an abnormal uGAG pattern confirms an MPS disorder and specific enzyme testing will determine the MPS type. If uGAG analysis is unavailable and the patient exhibits any other common sign or symptom of an MPS disorder, such as corneal clouding, history of hernia surgery, frequent respiratory and/or ear, nose and throat infections; carpal tunnel syndrome, or heart murmur, proceed directly to enzymatic testing. Refer patients with confirmed MPS to a geneticist or metabolic specialist for further evaluation and treatment.

TESTING OF THE HYPOTHESIS

We propose that rheumatologists, pediatric rheumatologists, and orthopedists consider our diagnostic algorithm when evaluating patients with joint pain and joint contractures.

IMPLICATIONS OF THE HYPOTHESIS

Children and young adults can suffer for years and sometimes even decades with unrecognized MPS. Rheumatologists may facilitate early diagnosis of MPS based on the presenting signs and symptoms, followed by appropriate testing. Early diagnosis helps ensure prompt and appropriate treatment for these progressive and debilitating diseases.

A systematic review of new advances in the management of mucopolysaccharidosis VI (Maroteaux-Lamy syndrome): focus on galsulfase

Introduction

Mucopolysaccharidosis type VI (MPS VI, Maroteaux-Lamy syndrome) is an autosomal recessive lysosomal storage disorder, characterized primarily by skeletal dysplasia and joint contracture. It is caused by a deficiency of N-acetylgalactosamine-4-sulfatase (arylsulfatase B), for which a recombinant formulation (galsulfase) is available as replacement therapy.

Objective

To evaluate the effectiveness and safety of galsulfase compared to placebo or no interventions, for treating MPS VI. We also considered studies evaluating different doses of galsulfase.

Methods

A systematic review of the literature was conducted. A computerized electronic search in MEDLINE, EMBASE, CENTRAL, SciELO, and LILACS was carried on to identify any randomized trials that met our inclusion criteria.

Results

Two studies were included in the review. Because the number of studies was small, our analysis probably did not find any statistically significant difference. Long-term follow-up will be required to ascertain full clinical benefit, on both event-free survival and quality of life measures.

Conclusions

There is some evidence to support the use of galsulfase in the treatment of MPS VI; however due to the very low quantity of included studies we could not analyze it in an appropriate way. This review highlights the need for continued research into the use of enzyme replacement therapy for MPS VI.

Multiple sulfatase deficiency: clinical report and description of two novel mutations in a Brazilian patient

Multiple Sulfatase Deficiency (MSD) is a rare autosomal recessive disease in which the activities of all sulfatases are reduced; its estimated prevalence is 1:1.4 million births. The disease is caused by mutations in SUMF1, which encodes an enzyme involved in the post-translational modification of sulfatases. The MSD phenotype is a combination of the clinical features found in diseases resulting from a deficiency of the individual sulfatases; i.e., mucopolysaccharidosis II, IIIA, IIID, IVA and VI, metachromatic leukodystrophy, X-linked ichthyosis, and the X-linked recessive form of chondrodysplasia punctata. We describe herein the first case of a Brazilian patient with MSD. The case was initially diagnosed as having mucopolysaccharidosis (MPS), due to skeletal alterations, coarse facial features, and urinary excretion of dermatan sulfate and heparan sulfate. Later, after a detailed biochemical investigation, the diagnosis of MSD was established. The analysis of the SUMF1 showed the patient was a compound heterozygote for two novel mutations (p.R349G and p.F244S). This case illustrates the challenges in the diagnosis of a disease considered rare, such as MSD. We point out that the availability of therapy for certain MPS disorders necessitates correct disease assignment, and the need to exclude the likelihood of MSD.

To see a world in a grain of sand: elucidating the pathophysiology of Anderson-Fabry disease through investigations of a cellular model

Thomaidis and colleagues have created a cellular model of Anderson-Fabry disease by 'silencing' alpha-galactosidase A (AGAL) activity in human tubular epithelial cells. Increased membrane globotriaosylceramide (Gb3/CD77) expression was observed; it is suggested that this finding may be potentially useful as a surrogate marker of disease severity. Decreased membrane Gb3/CD77 expression was observed following agalsidase-alpha treatment, providing evidence of changes in cellular phenotype in response to enzyme therapy.

Variable expression of a novel PLP1 mutation in members of a family with Pelizaeus-Merzbacher disease

Pelizaeus-Merzbacher disease is a rare X-linked disorder caused by mutations of the proteolipid protein 1 gene that encodes a structural component of myelin. It is characterized by progressive psychomotor delay, nystagmus, spastic quadriplegia, and cerebellar ataxia. Variable clinical expression was seen in 5 members of a family bearing a novel missense mutation in proteolipid protein 1, c.619T>C. Symptomatic patients included a 6-year-old girl, her younger brother, and their maternal uncle, a 29-year-old college graduate initially diagnosed with cerebral palsy; their brain magnetic resonance imaging studies showed diffuse dysmyelination. The mother had a history of delayed walking, achieved independently by age 3; she and the maternal grandmother were asymptomatic on presentation. Review of clinical information and family history led to consideration of Pelizaeus-Merzbacher disease. Subsequent identification of the causal mutation enabled preimplantation genetic diagnosis and the birth of an unaffected child.

A randomized trial comparing the efficacy and safety of imiglucerase (Cerezyme) infusions every 4 weeks versus every 2 weeks in the maintenance therapy of adult patients with Gaucher disease type 1

Imiglucerase (Cerezyme) has been the standard of care for treatment of Gaucher disease, a lysosomal storage disorder resulting from deficiency of glucocerebrosidase, since its approval in 1994. Infusions are typically given once every 2 weeks. However, many patients have expressed a desire for less frequent infusions as a matter of convenience. This clinical study assessed the safety and efficacy of intravenous imiglucerase infused once every 4 weeks (Q4) compared to once every 2 weeks (Q2) at the same total monthly dose in adult patients with clinically stable Gaucher disease type 1 (GD1). This was a 24-month, open-label, randomized, Phase 4, dose-frequency study conducted in 25 centers worldwide. Patients receiving imiglucerase were randomized to receive their monthly dose biweekly (n=33) or every 4 weeks (n=62). Changes from baseline in hemoglobin, platelets, liver and spleen volumes, bone crisis, and bone disease comprised a predefined composite endpoint; achievement or maintenance of established Gaucher disease therapeutic goals comprised a secondary endpoint. Sixty-three percent of Q4- and 81% of Q2-treated patients met the composite endpoint at Month 24; 89% of Q4- and 100% of Q2-treated patients met the therapeutic goals-based endpoint. The frequency of related adverse events was comparable between treatment groups. This study suggests that with comprehensive monitoring, a Q4 imiglucerase infusion regimen may be a safe and effective treatment option for the majority of clinically stable adult patients with GD1 but may not be appropriate for all GD1 patients. Continued monitoring in patients treated with Q4 dosing is required to assess long-term effectiveness.

The underrecognized progressive nature of N370S Gaucher disease and assessment of cancer risk in 403 patients

Mutations in GBA1 gene that encodes lysosomal glucocerebrosidase result in Type 1 Gaucher Disease (GD), the commonest lysosomal storage disorder; the most prevalent disease mutation is N370S. We investigated the heterogeneity and natural course of N370S GD in 403 patients. Demographic, clinical, and genetic characteristics of GD at presentation were examined in a cross-sectional study. In addition, the relative risk (RR) of cancer in patients compared with age-, sex-, and ethnic-group adjusted national rates of cancer was determined. Of the 403 patients, 54% of patients were homozygous (N370S/N370S) and 46% were compound heterozygous for the N370S mutation (N370S/other). The majority of N370S/N370S patients displayed a phenotype characterized by late onset, predominantly skeletal disease, whereas the majority of N370S/other patients displayed early onset, predominantly visceral/hematologic disease, P < 0.0001. There was a striking increase in lifetime risk of multiple myeloma in the entire cohort (RR 25, 95% CI 9.17-54.40), mostly confined to N370S homozygous patients. The risk of other hematologic malignancies (RR 3.45, 95% CI 1.49-6.79), and overall cancer risk (RR 1.80, 95% CI 1.32-2.40) was increased. Homozygous N370S GD leads to adult-onset progressive skeletal disease with relative sparing of the viscera, a strikingly high risk of multiple myeloma, and an increased risk of other cancers. High incidence of gammopathy suggests an important role of the adaptive immune system in the development of GD. Adult patients with GD should be monitored for skeletal disease and cancers including multiple myeloma.

Musculoskeletal complications encountered in the lysosomal storage disorders

The lysosomal storage disorders are a heterogeneous group of inherited metabolic diseases resulting from defects in the degradation or transport of several distinct by-products of cellular turnover. The various subtypes are characterized by multi-systemic involvement; the wide range in patient ages at symptom onset is only partly explained by the underlying mutation(s). Neurodegenerative features and musculoskeletal complications are often seen in the most severe variants, and are features of the disease that have the most significant impact on patients' physical and functional well-being. Until recently, the care of affected individuals relied mainly on palliative or supportive measures. The introduction of therapies directed at correcting the primary defect (i.e., deficient enzyme activity) in several of these disorders has led to modification of the phenotype and natural history or disease course; however, clinical problems arising from brain and bone involvement remain major sources of morbidity. Factors that might influence therapeutic outcome include pre-existing pathology at the time of treatment initiation, drug access to tissues sites of pathology, and - in the case of enzyme therapy - antibody formation. Increasing understanding of the pathogenesis or relevant mechanism(s) of diseases is providing insights into additional therapeutic targets, enabling the potential for optimized patient outcomes with the use of adjunctive or supplemental agents. Physical and occupational therapy remain critical components of a comprehensive approach to patient care.

Long-term efficacy and safety of laronidase in the treatment of mucopolysaccharidosis I

OBJECTIVE

Our goal was to evaluate the long-term safety and efficacy of recombinant human alpha-l-iduronidase (laronidase) in patients with mucopolysaccharidosis I.

PATIENTS AND METHODS

All 45 patients who completed a 26-week, double-blind, placebo-controlled trial of laronidase were enrolled in a 3.5-year open-label extension study. Mean patient age at baseline was 16 (range: 6-43) years. All patients had attenuated disease (84% Hurler-Scheie, 16% Scheie phenotypes). Clinical, biochemical, and health outcomes measures were evaluated through the extension phase. Changes are presented as the mean +/- SEM.

RESULTS

All 40 patients (89%) who completed the trial received at least 80% of scheduled infusions. As shown in earlier trials, urinary glycosaminoglycan levels decreased within the first 12 weeks and liver volume decreased within the first year. Percent predicted forced vital capacity remained stable, with a linear slope of -0.78 percentage points per year. The 6-minute walk distance increased 31.7 +/- 10.2 m in the first 2 years, with a final gain of 17.1 +/- 16.8 m. Improvements in the apnea/hypopnea index (decrease of 7.6 +/- 4.5 events per hour among the patients with significant baseline sleep apnea) and shoulder flexion (increase of 17.4 degrees +/- 3.6 degrees) were most rapid during the first 2 years. Improvements in the Child Health Assessment Questionnaire/Health Assessment Questionnaire disability index (decrease of 0.31 +/- 0.11, signifying a clinically meaningful improvement in activities of daily living) were gradual and sustained over the treatment period. Laronidase infusions were generally well tolerated except in 1 patient who experienced an anaphylactic reaction. Infusion-associated reactions, which occurred in 53% of the patients, were mostly mild, easily managed, and decreased markedly after 6 months. One patient died as a result of an upper respiratory infection unrelated to treatment. Antibodies to laronidase developed in 93% of the patients; 29% of the patients were seronegative at their last assessment.

CONCLUSIONS

This trial demonstrates the long-term clinical benefit and safety of laronidase in attenuated patients with mucopolysaccharidosis I and highlights the magnitude and chronology of treatment effects. Prompt diagnosis and early treatment will maximize treatment outcomes.