Pompe disease in adulthood: effects of antibody formation on enzyme replacement therapy.

PURPOSE: To determine the effect of antibodies against recombinant human acid α-glucosidase (rhGAA) on treatment efficacy and safety, and to test whether the GAA genotype is involved in antibody formation. METHODS: We used enzyme-linked immunosorbent assay (ELISA) to determine anti-rhGAA antibody titers at baseline and at 6, 12, and 36 months of rhGAA treatment. We measured the capacity of antibodies to neutralize rhGAA enzymatic activity or cellular uptake and the effects on infusion-associated reactions (IARs), muscle strength, and pulmonary function. RESULTS: Of 73 patients, 45 developed antibodies. Maximal titers were high (≥1:31,250) in 22% of patients, intermediate (1:1,250-1:31,250) in 40%, and none or low (0-1:1,250) in 38%. The common IVS1/delex18 GAA genotype was absent only in the high-titer group. The height of the titer positively correlated with the occurrence and number of IARs (P ≤ 0.001). On the group level, antibody titers did not correlate with treatment efficacy. Eight patients (11%) developed very high maximal titers (≥156,250), but only one patient showed high sustained neutralizing antibodies that probably interfered with treatment efficacy. CONCLUSIONS: In adults with Pompe disease, antibody formation does not interfere with rhGAA efficacy in the majority of patients, is associated with IARs, and may be attenuated by the IVS1/delex18 GAA genotype.Genet Med 19 1, 90-97.

Quality of life and participation in daily life of adults with Pompe disease receiving enzyme replacement therapy: 10 years of international follow-up.

BACKGROUND: Pompe disease is an inheritable metabolic disorder for which enzyme replacement therapy (ERT) has been available since 2006. Effects of ERT have been shown on distance walked, pulmonary function and survival. We investigated whether it also improves quality of life and participation in daily life in adult patients with the disease. METHODS: In an international survey, we assessed quality of life (Short Form 36, SF-36) and participation (Rotterdam Handicap Scale, RHS) annually between 2002 and 2012. Repeated measurements mixed effects models were used to describe the data over time. RESULTS: Responses were available for 174 adult patients. In the periods before and after start of ERT, the median follow-up times were 4 years each (range 0.5-8). The SF-36 Physical Component Summary measure (PCS) deteriorated before ERT (-0.73 score points per year (sp/y); CI 95 % -1.07 to -0.39), while it improved in the first 2 years of ERT (1.49 sp/y; CI 0.76 to 2.21), and remained stable thereafter. The Mental Component Summary measure (MCS) remained stable before and during ERT. After declining beforehand (-0.49 sp/year; CI -0.64 to-0.34), the RHS stabilized under ERT. CONCLUSION: In adult patients with Pompe disease, ERT positively affects quality of life and participation in daily life. Our results reinforce previous findings regarding the effect of ERT on muscle strength, pulmonary function and survival.

Exercise training in adults with Pompe disease: the effects on pain, fatigue, and functioning.

OBJECTIVE: To assess if a 12-week exercise intervention to improve aerobic fitness, muscle strength, and core stability also had an impact on fatigue, pain, activity, and participation in adults with Pompe disease, an inherited neuromuscular disorder. DESIGN: Open-label trial. Change was assessed by the chi-square test and Wilcoxon signed-rank test. SETTING: Physiotherapy practices. PARTICIPANTS: Mildly affected adult patients with Pompe disease who were not dependent on ventilators and/or walking devices and were receiving enzyme replacement therapy. INTERVENTION: Patients participated in a 12-week exercise program, which included 36 sessions of standardized aerobic, resistance, and core stability exercises. MAIN OUTCOME MEASURES: Before and after the training program we evaluated fatigue (Fatigue Severity Scale), pain (yes/no), motor function (Quantitative Muscle Function Test, Rasch-built Pompe-specific Activity Scale), amount of physical activity (activity monitor), and health status (Medical Outcomes Study 36-Item Short-Form Health Survey). RESULTS: Of the 25 patients enrolled, 23 completed the program. At the end of the program, levels of fatigue (median, 5.33 to 4.78, P=.01) and pain (56.5% to 21.7%, P=.04) improved. The quality of motor function and the amount of physical activity patients engaged in did not change. Changes in pain and fatigue were not related to improvements in aerobic fitness or muscle strength. CONCLUSIONS: This study in mildly affected adult patients with Pompe disease suggests that a combined training program aiming to increase aerobic fitness, muscle strength, and core stability also leads to improvements in fatigue and pain.

Lung MRI and impairment of diaphragmatic function in Pompe disease.

BACKGROUND: Pompe disease is a progressive metabolic myopathy. Involvement of respiratory muscles leads to progressive pulmonary dysfunction, particularly in supine position. Diaphragmatic weakness is considered to be the most important component. Standard spirometry is to some extent indicative but provides too little insight into diaphragmatic dynamics. We used lung MRI to study diaphragmatic and chest-wall movements in Pompe disease. METHODS: In ten adult Pompe patients and six volunteers, we acquired two static spirometer-controlled MRI scans during maximum inspiration and expiration. Images were manually segmented. After normalization for lung size, changes in lung dimensions between inspiration and expiration were used for analysis; normalization was based on the cranial-caudal length ratio (representing vertical diaphragmatic displacement), and the anterior-posterior and left-right length ratios (representing chest-wall movements due to thoracic muscles). RESULTS: We observed striking dysfunction of the diaphragm in Pompe patients; in some patients the diaphragm did not show any displacement. Patients had smaller cranial-caudal length ratios than volunteers (p < 0.001), indicating diaphragmatic weakness. This variable strongly correlated with forced vital capacity in supine position (r = 0.88) and postural drop (r = 0.89). While anterior-posterior length ratios also differed between patients and volunteers (p = 0.04), left-right length ratios did not (p = 0.1). CONCLUSIONS: MRI is an innovative tool to visualize diaphragmatic dynamics in Pompe patients and to study chest-walland diaphragmatic movements in more detail. Our data indicate that diaphragmatic displacement may be severely disturbed in patients with Pompe disease.

Increased aortic stiffness and blood pressure in non-classic Pompe disease.

Vascular abnormalities and glycogen accumulation in vascular smooth muscle fibres have been described in Pompe disease. Using carotid-femoral pulse wave velocity (cfPWV), the gold standard methodology for determining aortic stiffness, we studied whether aortic stiffness is increased in patients with Pompe disease. Eighty-four adult Pompe patients and 179 age- and gender-matched volunteers participated in this cross-sectional case-controlled study. Intima media thickness and the distensibility of the right common carotid artery were measured using a Duplex scanner. Aortic augmentation index, central pulse pressure, aortic reflexion time and cfPWV were assessed using the SphygmoCor® system. CfPWV was higher in patients than in volunteers (8.8 versus 7.4 m/s, p < 0.001). This difference was still present after adjustment for age, gender, mean arterial blood pressure (MAP), heart rate and diabetes mellitus (p = 0.001), and was shown by subgroup analysis to apply to the 40-59 years age group (p = 0.004) and 60+ years age group (p = 0.01), but not to younger age groups (p = 0.99). Except for a shorter aortic reflexion time (p = 0.02), indirect indicators of arterial stiffness did not differ between patients and volunteers. Relative to volunteers (20%), more Pompe patients had a history of hypertension (36%, p = 0.005), and the MAP was higher than in volunteers (100 versus 92 mmHg, p < 0.001). This study shows that patients with non-classic Pompe disease have increased aortic stiffness and blood pressure. Whether this is due to glycogen accumulation requires further investigation. To reduce the potential risk of cardiovascular diseases, we recommend that blood pressure and other common cardiovascular risk factors are monitored regularly.

Remarkably low fibroblast acid α-glucosidase activity in three adults with Pompe disease.

INTRODUCTION: Most adults with Pompe disease are compound heterozygotes in which one acid α-glucosidase (GAA) allele harbors the c.-32-13T>G mutation, causing partial loss of GAA, and the other allele harbors a fully deleterious mutation. The fibroblast GAA activity in these patients is usually between 5% and 25% of the average in healthy individuals. In some adult patients, however, the fibroblast GAA activity is much lower and is in the range that is normally observed in classic-infantile Pompe disease. We investigated the genotype-phenotype correlation in three such adult patients and measured the GAA activity as well as the glycogen content in muscle and fibroblasts in order to better understand the clinical course. METHODS: DNA was sequenced and GAA activity and glycogen content were measured in leukocytes, fibroblasts and muscle. Muscle biopsies were microscopically analyzed and the biosynthesis of GAA in fibroblasts was analyzed by immunoblotting. GAA activity and glycogen content in fibroblasts and muscle tissue in healthy controls, adult patients with Pompe disease and classic-infantile patients were compared with those of the three index patients. RESULTS: One patient had genotype c.525delT/c.671G>A (r.0/p.Arg224Gln). Two affected brothers had genotype c.569G>A/c.1447G>A (p.Arg190His/p.Gly483Arg). In all three cases the GAA activity and the glycogen content in fibroblasts were within the same range as in classic-infantile Pompe disease, but the activity and glycogen content in muscle were both within the adult range. In fibroblasts, the first step of GAA synthesis appeared unaffected but lysosomal forms of GAA were not detectable with immunoblotting. CONCLUSION: Some adult patients with mutations other than c.-32-13T>G can have very low GAA activity in fibroblasts but express higher activity in muscle and store less glycogen in muscle than patients with classic-infantile Pompe disease. This might explain why these patients have a slowly progressive course of Pompe disease.

Long-term benefit of enzyme replacement therapy in Pompe disease: A 5-year prospective study.

OBJECTIVE: To determine the effect of enzyme replacement therapy (ERT) after 5 years and to identify predictors for a favorable response because few data are available on the long-term efficacy of ERT in Pompe disease. METHODS: We included 102 adult patients with Pompe disease in a nationwide, prospective cohort study. We assessed muscle strength (manual muscle testing with Medical Research Council [MRC] grading, handheld dynamometry [HHD]), muscle function (6-minute walk test, Quick Motor Function Test), daily life activities (Rasch-Built Pompe-Specific Activity [R-PAct] Scale), and pulmonary function (forced vital capacity [FVC] in upright and supine positions, maximum inspiratory and expiratory pressures) at 3- to 6-month intervals before and after the start of ERT. Data were analyzed with linear mixed-effects models for repeated measurements. RESULTS: Median follow-up duration was 6.1 years (range 0.4-7.9 years), of which 5.0 years (range 0.2-7.3 years) were during ERT. Treated patients had better muscle strength (MRC sum score +6.6 percentage points [pp]; HHD sum score +9.6 pp, both p < 0.0001), activity levels (R-PAct +10.8 pp, p < 0.002), and pulmonary function (FVC upright +7.3 pp, FVC supine +7.6 pp, both p < 0.0003) than expected for their untreated disease course. Walking distance improved (416 vs 376 m at baseline, p = 0.03). The largest increase was seen during the first 2 to 3 years of treatment. Response to treatment was similar between groups regardless of sex, age, or disease duration. CONCLUSIONS: Long-term ERT positively affects muscle strength, pulmonary function, and daily life activities in adult patients with Pompe disease, with a peak effect at ≈2 to 3 years of treatment. CLASSIFICATION OF EVIDENCE: This study provides Class IV evidence that for patients with Pompe disease, long-term ERT positively affects muscle strength, pulmonary function, and daily life activities.

Quantification of Diaphragm Mechanics in Pompe Disease Using Dynamic 3D MRI.

BACKGROUND: Diaphragm weakness is the main reason for respiratory dysfunction in patients with Pompe disease, a progressive metabolic myopathy affecting respiratory and limb-girdle muscles. Since respiratory failure is the major cause of death among adult patients, early identification of respiratory muscle involvement is necessary to initiate treatment in time and possibly prevent irreversible damage. In this paper we investigate the suitability of dynamic MR imaging in combination with state-of-the-art image analysis methods to assess respiratory muscle weakness. METHODS: The proposed methodology relies on image registration and lung surface extraction to quantify lung kinematics during breathing. This allows for the extraction of geometry and motion features of the lung that characterize the independent contribution of the diaphragm and the thoracic muscles to the respiratory cycle. RESULTS: Results in 16 3D+t MRI scans (10 Pompe patients and 6 controls) of a slow expiratory maneuver show that kinematic analysis from dynamic 3D images reveals important additional information about diaphragm mechanics and respiratory muscle involvement when compared to conventional pulmonary function tests. Pompe patients with severely reduced pulmonary function showed severe diaphragm weakness presented by minimal motion of the diaphragm. In patients with moderately reduced pulmonary function, cranial displacement of posterior diaphragm parts was reduced and the diaphragm dome was oriented more horizontally at full inspiration compared to healthy controls. CONCLUSION: Dynamic 3D MRI provides data for analyzing the contribution of both diaphragm and thoracic muscles independently. The proposed image analysis method has the potential to detect less severe diaphragm weakness and could thus be used to determine the optimal start of treatment in adult patients with Pompe disease in prospect of increased treatment response.

Elevated Plasma Cardiac Troponin T Levels Caused by Skeletal Muscle Damage in Pompe Disease.

BACKGROUND: Elevated plasma cardiac troponin T (cTnT) levels in patients with neuromuscular disorders may erroneously lead to the diagnosis of acute myocardial infarction or myocardial injury. METHODS AND RESULTS: In 122 patients with Pompe disease, the relationship between cTnT, cardiac troponin I, creatine kinase (CK), CK-myocardial band levels, and skeletal muscle damage was assessed. ECG and echocardiography were used to evaluate possible cardiac disease. Patients were divided into classic infantile, childhood-onset, and adult-onset patients. cTnT levels were elevated in 82% of patients (median 27 ng/L, normal values <14 ng/L). Cardiac troponin I levels were normal in all patients, whereas CK-myocardial band levels were increased in 59% of patients. cTnT levels correlated with CK levels in all 3 subgroups (P<0.001). None of the abnormal ECGs recorded in 21 patients were indicative of acute myocardial infarction, and there were no differences in cTnT levels between patients with and without (n=90) abnormalities on ECG (median 28 ng/L in both groups). The median left ventricular mass index measured with echocardiography was normal in all the 3 subgroups. cTnT mRNA expression in skeletal muscle was not detectable in controls but was strongly induced in patients with Pompe disease. cTnT protein was identified by mass spectrometry in patient-derived skeletal muscle tissue. CONCLUSIONS: Elevated plasma cTnT levels in patients with Pompe disease are associated with skeletal muscle damage, rather than acute myocardial injury. Increased cTnT levels in Pompe disease and likely other neuromuscular disorders should be interpreted with caution to avoid unnecessary cardiac interventions.

Safety and efficacy of exercise training in adults with Pompe disease: evalution of endurance, muscle strength and core stability before and after a 12 week training program.

BACKGROUND: Pompe disease is a proximal myopathy. We investigated whether exercise training is a safe and useful adjuvant therapy for adult Pompe patients, receiving enzyme replacement therapy. METHODS: Training comprised 36 sessions of standardized aerobic, resistance and core stability exercises over 12 weeks. Before and after, the primary outcome measures safety, endurance (aerobic exercise capacity and distance walked on the 6 min walk test) and muscle strength, and secondary outcome measures core stability, muscle function and body composition, were evaluated. RESULTS: Of 25 patients enrolled, 23 successfully completed the training. Improvements in endurance were shown by increases in maximum workload capacity (110 W before to 122 W after training, [95 % CI of the difference 6 · 0 to 19 · 7]), maximal oxygen uptake capacity (69 · 4 % and 75 · 9 % of normal, [2 · 5 to 10 · 4]), and maximum walking distance (6 min walk test: 492 meters and 508, [-4 · 4 to 27 · 7] ). There were increases in muscle strength of the hip flexors (156 · 4 N to 180 · 7 N [1 · 6 to 13 · 6) and shoulder abductors (143 · 1 N to 150 · 7 N [13 · 2 to 35 · 2]). As an important finding in secondary outcome measures the number of patients who were able to perform the core stability exercises rose, as did the core stability balancing time (p < 0.05, for all four exercises). Functional tests showed small reductions in the time needed to climb four steps (2 · 4 sec to 2 · 1, [- 0 · 54 to -0 · 04 ]) and rise to standing position (5 · 8 sec to 4 · 8, [-2 · 0 to 0 · 0]), while time to run, the quick motor function test results and body composition remained unchanged. CONCLUSIONS: Our study shows that a combination of aerobic, strength and core stability exercises is feasible, safe and beneficial to adults with Pompe disease.

Phenotypical variation within 22 families with Pompe disease.

BACKGROUND: Pompe disease has a broad clinical spectrum, in which the phenotype is partially explained by the genotype. The aim of this study was to describe phenotypical variation among siblings with non-classic Pompe disease. We hypothesized that siblings and families with the same genotype share more similar phenotypes than the total population of non-classic Pompe patients, and that this might reveal genotype-phenotype correlations. METHODS: We identified all Dutch families in which two or three siblings were diagnosed with Pompe disease and described genotype, acid α-glucosidase activity, age at symptom onset, presenting symptoms, specific clinical features, mobility and ventilator dependency. RESULTS: We identified 22 families comprising two or three siblings. All carried the most common mutation c.-32-13 T > G in combination with another pathogenic mutation. The median age at symptom onset was 33 years (range 1-62 years). Within sibships symptom onset was either in childhood or in adulthood. The median variation in symptom onset between siblings was nine years (range 0-31 years). Presenting symptoms were similar across siblings in 14 out of 22 families. Limb girdle weakness was most frequently reported. In some families ptosis or bulbar weakness were present in all siblings. A large variation in disease severity (based on wheelchair/ventilator dependency) was observed in 11 families. This variation did not always result from a difference in duration of the disease since a third of the less affected siblings had a longer course of the disease. Enzyme activity could not explain this variation either. In most families male patients were more severely affected. Finally, symptom onset varied substantially in twelve families despite the same GAA genotype. CONCLUSION: In most families with non-classic Pompe disease siblings share a similar phenotype regarding symptom onset, presenting symptoms and specific clinical features. However, in some families the course and severity of disease varied substantially. This phenotypical variation was also observed in families with identical GAA genotypes. The commonalities and differences indicate that besides genotype, other factors such as epigenetic and environmental effects influence the clinical presentation and disease course.