Phase I study of liver depot gene therapy in late-onset Pompe disease.

Gene therapy with an adeno-associated virus serotype 8 (AAV8) vector (AAV8-LSPhGAA) could eliminate the need for enzyme replacement therapy (ERT) by creating a liver depot for acid α-glucosidase (GAA) production. We report initial safety and bioactivity of the first dose (1.6 × 1012 vector genomes/kg) cohort (n = 3) in a 52-week open-label, single-dose, dose-escalation study (NCT03533673) in patients with late-onset Pompe disease (LOPD). Subjects discontinued biweekly ERT after week 26 based on the detection of elevated serum GAA activity and the absence of clinically significant declines per protocol. Prednisone (60 mg/day) was administered as immunoprophylaxis through week 4, followed by an 11-week taper. All subjects demonstrated sustained serum GAA activities from 101% to 235% of baseline trough activity 2 weeks following the preceding ERT dose. There were no treatment-related serious adverse events. No subject had anti-capsid T cell responses that decreased transgene expression. Muscle biopsy at week 24 revealed unchanged muscle glycogen content in two of three subjects. At week 52, muscle GAA activity for the cohort was significantly increased (p < 0.05). Overall, these initial data support the safety and bioactivity of AAV8-LSPhGAA, the safety of withdrawing ERT, successful immunoprophylaxis, and justify continued clinical development of AAV8-LSPhGAA therapy in Pompe disease.

Glucosylsphingosine (Lyso-Gb1): An Informative Biomarker in the Clinical Monitoring of Patients with Gaucher Disease.

Historically, disease burden and treatment responses in patients with Gaucher disease (GD) was assessed by monitoring clinical data, laboratory, imaging, chitotriosidase (CHITO), and other biomarkers; however, these biomarkers lack specificity and CHITO is uninformative in patients heterozygous or homozygous for the CHIT1 c.1049_1072dup24 variant. Recently, glucosylsphingosine (lyso-Gb1), a sensitive and specific GD biomarker, has been recommended for patient monitoring. Furthermore, studies measuring lyso-Gb1 and CHITO in patients on long-term treatment with enzyme replacement therapy (ERT) and/or substrate reduction therapy (SRT) reported as group data show a reduction in both analytes, yet individualized patient data are generally unavailable. We describe seven patients on long-term treatment with longitudinal clinical data with monitoring based on current treatment guidelines. We present four patients who exhibit stable disease with normalized CHITO despite elevated lyso-Gb1. We present one patient who transitioned from ERT to SRT due to lack of a clinical response with life-threatening thrombocytopenia who responded with marked improvement in platelets, and normalized levels of both CHITO and lyso-Gb1. Finally, we present two ERT to SRT switch patients with stable disease on ERT who exhibited non-compliance on SRT, one with mirrored marked elevations of CHITO and lyso-Gb1; and another with normal CHITO and platelets, but increasing lyso-Gb1 levels and enlarged spleen. These clinical vignettes highlight the role of lyso-Gb1 as a sensitive biomarker in management of patients with GD, and its further value when CHITO is normal and thus uninformative. We highlight the personalized medicine approach needed to optimize treatment outcomes and recommendations for these patients.

Higher dosing of alglucosidase alfa improves outcomes in children with Pompe disease: a clinical study and review of the literature.

PURPOSE: Enzyme replacement therapy (ERT) with recombinant human acid-α glucosidase (rhGAA) at standard dose of 20 mg/kg every other week is insufficient to halt the long-term progression of myopathy in Pompe disease. METHODS: We conducted a retrospective study on infantile-onset Pompe disease (IPD) and late-onset Pompe disease (LOPD) patients with onset before age 5 years, ≥12 months of treatment with standard dose ERT, and rhGAA immunogenic tolerance prior to dose escalation. Long-term follow-up of up to 18 years was obtained. We obtained physical therapy, lingual strength, biochemical, and pulmonary assessments as dose was escalated. RESULTS: Eleven patients with IPD (n = 7) or LOPD (n = 4) were treated with higher doses of up to 40 mg/kg weekly. There were improvements in gross motor function measure in 9/10 patients, in lingual strength in 6/6 patients, and in pulmonary function in 4/11. Significant reductions in urinary glucose tetrasaccharide, creatine kinase, aspartate aminotransferase, and alanine aminotransferase were observed at 40 mg/kg weekly compared with lower doses (p < 0.05). No safety or immunogenicity concerns were observed at higher doses. CONCLUSION: Higher rhGAA doses are safe, improve gross motor outcomes, lingual strength, pulmonary function measures, and biochemical markers in early-onset Pompe disease, and should be considered in patients with clinical and functional decline.

Enzyme replacement therapy with alglucosidase alfa in Pompe disease: Clinical experience with rate escalation.

Patients with Pompe disease have realized significant medical benefits due to enzyme replacement therapy (ERT) infusions with alglucosidase alfa. However, regular infusions are time-consuming. Utilizing recommended infusion rates, infusion duration is 3h 45min for a patient receiving the standard dose of 20mg/kg, not including additional time needed for preparation of ERT, assessment of vital signs, intravenous access, and post-infusion monitoring. Recent studies have demonstrated increased effectiveness of higher dose of ERT (40mg/kg) in infantile-onset Pompe disease (IOPD), which increases the infusion duration to 6h 36min. Increased infusion durations compound the psychosocial burden on patients and families and potentially further disrupt family activities and obligations. We developed a stepwise infusion rate escalation protocol to administer higher dose ERT safely while decreasing infusion duration, which has been implemented in 15 patients to date. Reported here in detail are five patients with IOPD on 40mg/kg/weekly ERT in whom infusion duration was decreased with individualized, stepwise rate escalation. All patients tolerated rate escalations above the recommended rates without experiencing any infusion associated reactions and experienced a reduction in infusion duration by 1h and 24min with a corresponding increase in reported satisfaction. Our experience with ERT rate escalation is presented. SYNOPSIS: A careful stepwise method of enzyme replacement therapy (ERT) rate escalation can safely reduce infusion duration in patients with Pompe disease.

Sensitivity of whole exome sequencing in detecting infantile- and late-onset Pompe disease.

Pompe disease is a metabolic myopathy with a wide spectrum of clinical presentation. The gold-standard diagnostic test is acid alpha-glucosidase assay on skin fibroblasts, muscle or blood. Identification of two GAA pathogenic variants in-trans is confirmatory. Optimal effectiveness of enzyme replacement therapy hinges on early diagnosis, which is challenging in late-onset form of the disease due to non-specific presentation. Next-generation sequencing-based panels effectively facilitate diagnosis, but the sensitivity of whole-exome sequencing (WES) in detecting pathogenic GAA variants remains unknown. We analyzed WES data from 93 patients with confirmed Pompe disease and GAA genotypes based on PCR/Sanger sequencing. After ensuring that the common intronic variant c.-32-13T>G is not filtered out, whole-exome sequencing identified both GAA pathogenic variants in 77/93 (83%) patients. However, one variant was missed in 14/93 (15%), and both variants were missed in 2/93 (2%). One complex indel leading to a severe phenotype was incorrectly called a nonsynonymous substitution c.-32-13T>C due to misalignment. These results demonstrate that WES may fail to diagnose Pompe disease. Clinicians need to be aware of limitations of WES, and consider tests specific to Pompe disease when WES does not provide a diagnosis in patients with proximal myopathy, progressive respiratory failure or other subtle symptoms.

Longitudinal polysomnographic findings in infantile Pompe disease.

Infantile Pompe disease is a rare, metabolic disorder due to deficiency of the enzyme acid α-glucosidase that degrades lysosomal glycogen. The deficiency leads to multisystem dysfunction. Neuromuscular weakness due to metabolic myopathy is present, which predisposes children to sleep-disordered breathing. With the advent of enzyme replacement therapy (ERT), children are living longer, and there is a new natural history that is emerging. In a prior paper on our cohort of infantile Pompe disease patients, we reported a high incidence of both hypoventilation and obstructive sleep apnea (OSA). In this retrospective study, we analyzed longitudinal nocturnal polysomnography results from 10 patients with infantile-onset Pompe disease, all of which were on enzyme replacement therapy for a mean of 34.9 months at the time of follow-up study. Patients demonstrated relative stability in sleep disordered breathing, with a trend towards improvement in both OSA and central sleep apnea. ERT may help in the treatment of sleep apnea in this cohort.

Low anal sphincter tone in infantile-onset Pompe Disease: an emerging clinical issue in enzyme replacement therapy patients requiring special attention.

Pompe Disease (PD) is a lysosomal storage disease caused by acid α-glucosidase deficiency. The infantile form typically results in death in the first year of life. Patient survival has improved with enzyme replacement therapy (ERT), but new complications are being recognized. We report three cases of infantile onset PD on ERT who present with a new finding of poor anal tone, a finding that requires special attention for further complications such as rectal prolapse.

Polysomnographic findings in infantile Pompe disease.

Infantile Pompe disease is a rare, autosomal recessive disorder due to deficiency of the enzyme acid α-glucosidase that degrades lysosomal glycogen. Clinical features of diffuse hypotonia, cardiomyopathy, and weakness are present within the first days to months of life in patients with classic infantile Pompe disease. Progression of the disease often leads to respiratory failure. Although sleep apnea is reported in late-onset Pompe disease, sleep pathology is not well characterized in infantile disease. In this retrospective study, we analyzed nocturnal polysomnography results from 17 patients with infantile-onset Pompe disease. Obstructive sleep apnea and hypoventilation were common among this cohort, even in those that did not have symptoms of sleep-disordered breathing. All patients with infantile-onset Pompe disease should undergo polysomnography as a routine part of their care.

The emerging phenotype of long-term survivors with infantile Pompe disease.

PURPOSE: Enzyme replacement therapy with alglucosidase alfa for infantile Pompe disease has improved survival creating new management challenges. We describe an emerging phenotype in a retrospective review of long-term survivors. METHODS: Inclusion criteria included ventilator-free status and age ≤6 months at treatment initiation, and survival to age ≥5 years. Clinical outcome measures included invasive ventilator-free survival and parameters for cardiac, pulmonary, musculoskeletal, gross motor, and ambulatory status; growth; speech, hearing, and swallowing; and gastrointestinal and nutritional status. RESULTS: Eleven of 17 patients met study criteria. All were cross-reactive immunologic material-positive, alive, and invasive ventilator-free at most recent assessment, with a median age of 8.0 years (range: 5.4-12.0 years). All had marked improvements in cardiac parameters. Commonly present were gross motor weakness, motor speech deficits, sensorineural and/or conductive hearing loss, osteopenia, gastroesophageal reflux, and dysphagia with aspiration risk. Seven of 11 patients were independently ambulatory and four required the use of assistive ambulatory devices. All long-term survivors had low or undetectable anti-alglucosidase alfa antibody titers. CONCLUSION: Long-term survivors exhibited sustained improvements in cardiac parameters and gross motor function. Residual muscle weakness, hearing loss, risk for arrhythmias, hypernasal speech, dysphagia with risk for aspiration, and osteopenia were commonly observed findings.

An individually, modified approach to desensitize infants and young children with Pompe disease, and significant reactions to alglucosidase alfa infusions.

PURPOSE: Pompe disease (PD) is a progressive metabolic myopathy for which the only available treatment is alglucosidase alfa (Myozyme®). Enzyme replacement therapy (ERT) has improved ventilator-free survival, and cardiac and motor functions in patients with infantile PD. However, for an adequate response to occur, a large amount of enzymes must be infused. In some patients, this may be problematic due to infusion-associated reactions (IARs) occurring in approximately 50% of patients receiving alglucosidase alfa infusions. Whilst the majority of these reactions are mild, life threatening hypersensitivity reactions may occur in some patients. In these patients desensitization is indicated to enable continued ERT safely. Infants and young children with PD and significant infusion reactions pose unique management challenges because of their young age, limited communication skills, variable presentation and underlying cardiomyopathy. METHODS/SUBJECTS: In 2 patients with PD who experienced significant ERT-related reactions: an infant (IgE positive) and a young child (IgE negative), we implemented a desensitization protocol, that started by administering a reduced dose of alglucosidase alfa (10 mg/kg weekly) instead of the standard (20 mg/kg bi-weekly) using serial micro-dilutions that were individually prepared and delivered in a highly regulated manner based on patients' clinical manifestations and tolerance. RESULTS: Successful desensitization was achieved in both patients, allowing them to eventually continue to receive the full dose of ERT safely. CONCLUSION: Therapeutic demands in infants and young children with PD need to be tailored according to the patient presentation, and underlying cardiac and fluid-volume status. Desensitization allowed both patients to continue alglucosidase alfa treatment at the recommended dose without prolonged interruption of therapy, or further reactions.

Cross-reactive immunologic material status affects treatment outcomes in Pompe disease infants.

Deficiency of acid alpha glucosidase (GAA) causes Pompe disease, which is usually fatal if onset occurs in infancy. Patients synthesize a non-functional form of GAA or are unable to form native enzyme. Enzyme replacement therapy with recombinant human GAA (rhGAA) prolongs survival in infantile Pompe patients but may be less effective in cross-reactive immunologic material (CRIM)-negative patients. We retrospectively analyzed the influence of CRIM status on outcome in 21 CRIM-positive and 11 CRIM-negative infantile Pompe patients receiving rhGAA. Patients were from the clinical setting and from clinical trials of rhGAA, were 6 months of age, were not invasively ventilated, and were treated with IV rhGAA at a cumulative or total dose of 20 or 40 mg/kg/2 weeks. Outcome measures included survival, invasive ventilator-free survival, cardiac status, gross motor development, development of antibodies to rhGAA, and levels of urinary Glc(4). Following 52 weeks of treatment, 6/11 (54.5%) CRIM-negative and 1/21 (4.8%) CRIM-positive patients were deceased or invasively ventilated (p<0.0001). By age 27.1 months, all CRIM-negative patients and 4/21 (19.0%) CRIM-positive patients were deceased or invasively ventilated. Cardiac function and gross motor development improved significantly more in the CRIM-positive group. IgG antibodies to rhGAA developed earlier and serotiters were higher and more sustained in the CRIM-negative group. CRIM-negative status predicted reduced overall survival and invasive ventilator-free survival and poorer clinical outcomes in infants with Pompe disease treated with rhGAA. The effect of CRIM status on outcome appears to be mediated by antibody responses to the exogenous protein.

Use of cardiac magnetic resonance imaging to evaluate cardiac structure, function and fibrosis in children with infantile Pompe disease on enzyme replacement therapy.

BACKGROUND: Pompe disease (acid α-glucosidase deficiency) is one of several lysosomal storage diseases amenable to treatment with enzyme replacement therapy (ERT). While echocardiography (echo) has been the standard method to evaluate the cardiac response to ERT, cardiac magnetic resonance imaging (CMR) has the advantage of a better tissue definition and characterization of myocardial fibrosis. However, CMR for Pompe disease is not frequently performed due to a high risk of sedation. We report the first use of CMR in a feasible protocol to quantify left ventricular (LV) mass, function, and the presence of myocardial fibrosis in the Pompe population. METHODS: Children with Pompe disease on ERT were assessed with transthoracic echo and CMR over a 3 year period at a single institution. Echocardiography was performed using standard techniques without sedation. CMR was performed using retrospectively gated and real-time imaging, with and without sedation. LV mass indexed to body surface area (LVMI) and ejection fraction (EF) were measured by both echo and CMR, and evaluated for change over time. Myocardial fibrosis was assessed by CMR with delayed enhancement imaging 5-10 min after gadolinium contrast using single shot inversion recovery sequences with inversion time set to null the signal from normal myocardium. RESULTS: Seventeen CMR scans were successfully performed in 10 subjects with Pompe disease (median age at first CMR is 9 months, range 1-38 months, 80% male), with sedation only performed in 4 studies. There was a median interval of 5 months (range 0-34 months) from the start of ERT to first CMR (baseline). At baseline, the median indexed LVMI by CMR (140.0 g/m(2), range 43.8-334.0) tended to be lower than that assessed by echo (median 204.0 g/m(2), range 52.0-385.0), but did not reach statistical significance. At baseline, CMR EF was similar to that assessed by echo (55% vs. 55%). Overall, there was no significant decrease in CMR measured LVMI over time (CMR median LVMI at baseline 94 g/m(2) (range 43.8-334) vs. CMR median at most recent study 44.5 g/m(2) (range 34-303), p=0.44). In 5 patients with serial CMR scans over time, LVMI decreased in 2, was similar in 2, and increased in 1 patient with high sustained antibodies to exogenous enzyme. Delayed enhancement was noted in only l separate patient who also had high sustained antibodies to exogenous enzyme. CONCLUSION: CMR is an imaging tool that is feasible to use to serially follow LVMI and EF in children with Pompe disease on ERT. Real-time imaging is adequate for quantification purposes in these patients and minimizes the need for sedation. Quantitative CMR LVMI is generally lower than echo derived LVMI. Delayed enhancement appears to be a rare finding by CMR in Pompe disease. A further follow-up is necessary to better understand the long term effects of ERT in infantile Pompe survivors, especially those with high sustained antibody titers or advanced cardiac disease at treatment outset.

Pulmonary outcome measures in long-term survivors of infantile Pompe disease on enzyme replacement therapy: A case series.

OBJECTIVES: To report the respiratory function of school-aged children with infantile Pompe disease (IPD) who started enzyme replacement therapy (ERT) in infancy and early childhood. STUDY DESIGN: This is a retrospective chart review of pulmonary function tests of: (a) patients with IPD 5 to 18 years of age, (b) who were not ventilator dependent, and (c) were able to perform upright and supine spirometry. Subjects were divided into a younger (5-9 years) and older cohort (10-18 years) for the analysis. Upright and supine forced vital capacity (FVC), maximal inspiratory pressure (MIP), and maximal expiratory pressure (MEP) were analyzed. RESULTS: Fourteen patients, all cross-reactive immunologic material (CRIM)-positive, met the inclusion criteria and were included in this study. Mean upright and supine FVC were 70.3% and 64.9% predicted, respectively, in the 5- to 9-year-old cohort; and 61.5% and 52.5% predicted, respectively, in the 10- to 18-year-old group. Individual patient trends showed stability in FVC overtime in six of the 14 patients. MIPs and MEPs were consistent with inspiratory and expiratory muscle weakness in the younger and older age group but did not decline with age. CONCLUSION: Data from this cohort of CRIM-positive patients with IPD showed that ERT is able to maintain respiratory function in a subgroup of patients whereas others had a steady decline. There was a statistically significant decline in FVC from the upright to a supine position in both the younger and older age groups of CRIM-positive ERT-treated patients. Before ERT, patients with IPD were unable to maintain independent ventilation beyond the first few years of life.

Ectopic Ocular Surface Calcification in Patients With Hypophosphatasia Treated With Asfotase Alfa.

PURPOSE: To assess for ectopic ocular calcification in a series of patients with hypophosphatasia (HPP) treated with asfotase alfa, a recombinant tissue-nonspecific alkaline phosphatase. METHODS: This is a retrospective analysis of subjects enrolled at Duke University Medical Center in ENB-009-10 (ClinicalTrials.gov: NCT01163149), a randomized controlled trial of asfotase alfa in adolescents and adults with HPP. Seven patients between the ages of 45 and 66 years diagnosed with HPP based on clinical features and low serum alkaline phosphatase levels were enrolled at our site. Subjects were randomized to receive either daily subcutaneous injections of asfotase alfa or no treatment. After 24 weeks, during the open-label extension phase, all subjects received treatment for at least 4 years. All subjects underwent comprehensive eye examinations at baseline and at 24-week intervals throughout the study to assess for development of ocular calcifications. RESULTS: By week 120, all 7 subjects developed asymptomatic white refractile deposits in the interpalpebral perilimbal conjunctiva. Biopsy of the conjunctival lesions in 2 subjects revealed elastosis with subepithelial calcification. The lesions were nonprogressive and in 5 subjects exhibited some degree of regression. CONCLUSIONS: Asfotase alfa was invariably associated with development of mild focal conjunctival calcification, likely through disinhibition of hydroxyapatite crystal propagation. The calcifications were not symptomatic or vision-threatening and should not preclude enzyme replacement therapy for patients with this rare and often debilitating disease.

Improvement with ongoing Enzyme Replacement Therapy in advanced late-onset Pompe disease: a case study.

Benefits of enzyme replacement therapy with Myozyme (alglucosidase alfa), anecdotally reported in late-onset Pompe disease, range from motor and pulmonary improvement in less severely affected patients, to stabilization with minimal improvement in those with advanced disease. We report a case of a 63-year-old patient with significant morbidity who made notable motor and pulmonary function gains after two years on therapy. Thus, improvements in those with advanced disease may be possible after long-term treatment.

Corticobasal syndrome in a man with Gaucher disease type 1: Expansion of the understanding of the neurological spectrum.

Gaucher disease (GD) is an autosomal recessive condition that results from a deficiency of the enzyme ß-glucocerebrosidase. The increased risk of primary parkinsonism symptoms among individuals affected with GD and carriers for the disorder is well-documented in the literature. However, these risks and case reports often reflect patients with classical Parkinson's disease (PD) symptoms. We report a patient with GD type 1 who was diagnosed with corticobasal syndrome (CBS), a clinical atypical parkinsonism diagnosis, in his sixth decade of life. Our case highlights the need to consider forms of atypical parkinsonism such as CBS in addition to PD in the differential diagnosis of cognitive and motor changes in patients with GD type 1. We also recommend careful assessment and routine monitoring of cognition, mood, behavior, sleep patterns, olfaction, and memory in patients with GD type 1 to identify early symptoms indicative of neurological involvement.

Treatment of profound thrombocytopenia in a patient with Gaucher disease type 1: Is there a role for substrate reduction therapy.

The availability of three enzyme replacement therapy (ERT) drugs and two substrate reduction therapy (SRT) drugs to treat Gaucher disease provides an opportunity to tailor therapies to a patient's specific clinical concerns. However, there is a gap in the literature regarding individual drug effectiveness in treating particular symptoms and the potential benefits of combination treatment. This report details treatment of a patient with Gaucher disease type 1 whose main clinical concern was profound thrombocytopenia (around 20 × 109/L, normal range: 150-450 × 109/L) with several episodes of bleeding with minimal trauma and bruises. The patient was treated with ERT at doses up to 60 units/kg weekly, with no improvement in platelet levels for 6 years. Subsequently, the patient transitioned to SRT and platelet levels increased almost two fold within the first month, and have remained stable at safe levels (30-60 × 109/L) for almost 2.5 years at the time of publication. This report demonstrates a possible therapeutic benefit of SRT in individual patients who do not meet therapeutic goals in terms of thrombocytopenia after a considerable period on first-line ERT treatment. Oral administration of SRT also improved this patient's quality of life allowing discontinuation of weekly ERT infusions, which better accommodated her demanding career and busy lifestyle.

Case series: Odontohypophosphatasia or missed diagnosis of childhood/adult-onset hypophosphatasia? - Call for a long-term follow-up of premature loss of primary teeth.

INTRODUCTION: Hypophosphatasia, a metabolic bone disease caused by a tissue-nonspecific alkaline phosphatase deficiency, leads to undermineralization of bone and/or teeth, impaired vitamin B6 metabolism, and a spectrum of disease presentation. At the mild end of the spectrum, it presents as pathologic fractures in later adulthood. Patients with isolated dental manifestations, typically presenting as premature loss of primary teeth, are classified as having odontohypophosphatasia (odontoHPP). A subset of patients diagnosed with odontoHPP in childhood can later develop extra-dental manifestations that constitute childhood- or adult-onset hypophosphatasia. CASE REPORTS METHODS/RESULTS: Retrospective data related to onset, detailed clinical course, and method of diagnosis were collected as part of a natural history of adult patients with hypophosphatasia. Of 9 initial patients, all had low serum alkaline phosphatase levels for their age and gender at adult presentation (Table 2). The majority (8/9) demonstrated childhood dental signs of hypophosphatasia as the initial clinical manifestation: premature loss of primary teeth (7/9), absent primary teeth (1/9), and delayed loss of primary teeth (1/9). Despite childhood dental presentation and/or other signs/symptoms, diagnosis of hypophosphatasia was delayed 20-54 years (median = 46) since the primary tooth problems and 8-45 years (median = 27) since the first fracture or onset of a major adult tooth problem. CONCLUSION: Patients with primary tooth loss in childhood were often diagnosed with hypophosphatasia later in life. Pediatric patients classified as having odontoHPP under present practice can manifest significant disease burden later in life.

Safety and efficacy of alternative alglucosidase alfa regimens in Pompe disease.

Emerging phenotypes in long-term survivors with Pompe disease on standard enzyme replacement therapy (ERT) (alglucosidase alfa 20 mg/kg/2 weeks) can include patients with worsening motor function. Whether higher doses of ERT improve skeletal function in these patients has not been systematically studied. This exploratory, randomized, open-label, 52-week study examined the safety and efficacy of 2 ERT regimens of alglucosidase alfa (20 mg/kg/week or 40 mg/kg/2 weeks) in 13 patients with Pompe disease and clinical decline or a lack of improvement on standard ERT: late-onset (n = 4), infantile-onset (n = 9). Cross-reactive immunologic material assay-negative patients were excluded. Eleven of 13 patients completed the study. Trends for improvement were seen in total gross motor function, but not mobility; however, 6 (late-onset, 2; infantile-onset, 4) of 11 patients (55%) who met the entry criteria of motor decline (late-onset, 4; infantile-onset, 7) showed improvement in motor and/or mobility skills. No between-regimen differences in efficacy emerged. Two case studies highlight the benefits of increased ERT dose in patients with Pompe disease experiencing clinical decline. Both alternative regimens were generally well tolerated. This study was limited by the small sample size, which is not uncommon for small clinical studies of rare diseases. Additionally, the study did not include direct assessment of muscle pathology, which may have identified potential causes of decreased response to ERT. Results were inconclusive but suggest that increased ERT dose may be beneficial in some patients with Pompe disease experiencing motor decline. Controlled studies are needed to clarify the benefits and risks of this strategy.