Distribution of Exonic Variants in Glycogen Synthesis and Catabolism Genes in Late Onset Pompe Disease (LOPD).

Pompe disease (PD) is a monogenic autosomal recessive disorder caused by biallelic pathogenic variants of the GAA gene encoding lysosomal alpha-glucosidase; its loss causes glycogen storage in lysosomes, mainly in the muscular tissue. The genotype-phenotype correlation has been extensively discussed, and caution is recommended when interpreting the clinical significance of any mutation in a single patient. As there is no evidence that environmental factors can modulate the phenotype, the observed clinical variability in PD suggests that genetic variants other than pathogenic GAA mutations influence the mechanisms of muscle damage/repair and the overall clinical picture. Genes encoding proteins involved in glycogen synthesis and catabolism may represent excellent candidates as phenotypic modifiers of PD. The genes analyzed for glycogen synthesis included UGP2, glycogenin (GYG1-muscle, GYG2, and other tissues), glycogen synthase (GYS1-muscle and GYS2-liver), GBE1, EPM2A, NHLRC1, GSK3A, and GSK3B. The only enzyme involved in glycogen catabolism in lysosomes is α-glucosidase, which is encoded by GAA, while two cytoplasmic enzymes, phosphorylase (PYGB-brain, PGL-liver, and PYGM-muscle) and glycogen debranching (AGL) are needed to obtain glucose 1-phosphate or free glucose. Here, we report the potentially relevant variants in genes related to glycogen synthesis and catabolism, identified by whole exome sequencing in a group of 30 patients with late-onset Pompe disease (LOPD). In our exploratory analysis, we observed a reduced number of variants in the genes expressed in muscles versus the genes expressed in other tissues, but we did not find a single variant that strongly affected the phenotype. From our work, it also appears that the current clinical scores used in LOPD do not describe muscle impairment with enough qualitative/quantitative details to correlate it with genes that, even with a slightly reduced function due to genetic variants, impact the phenotype.

An integrative correlation of myopathology, phenotype and genotype in late onset Pompe disease.

AIMS: Pompe disease is caused by pathogenic mutations in the alpha 1,4-glucosidase (GAA) gene and in patients with late onset Pome disease (LOPD), genotype-phenotype correlations are unpredictable. Skeletal muscle pathology includes glycogen accumulation and altered autophagy of various degrees. A correlation of the muscle morphology with clinical features and the genetic background in GAA may contribute to the understanding of the phenotypic variability. METHODS: Muscle biopsies taken before enzyme replacement therapy were analysed from 53 patients with LOPD. On resin sections, glycogen accumulation, fibrosis, autophagic vacuoles and the degree of muscle damage (morphology-score) were analysed and the results were compared with clinical findings. Additional autophagy markers microtubule-associated protein 1A/1B-light chain 3, p62 and Bcl2-associated athanogene 3 were analysed on cryosections from 22 LOPD biopsies. RESULTS: The myopathology showed a high variability with, in most patients, a moderate glycogen accumulation and a low morphology-score. High morphology-scores were associated with increased fibrosis and autophagy highlighting the role of autophagy in severe stages of skeletal muscle damage. The morphology-score did not correlate with the patient's age at biopsy, disease duration, nor with the residual GAA enzyme activity or creatine-kinase levels. In 37 patients with LOPD, genetic analysis identified the most frequent mutation, c.-32-13T>G, in 95%, most commonly in combination with c.525delT (19%). No significant correlation was found between the different GAA genotypes and muscle morphology type. CONCLUSIONS: Muscle morphology in LOPD patients shows a high variability with, in most cases, moderate pathology. Increased pathology is associated with more fibrosis and autophagy.

Clinical characteristics and genotypes in the ADVANCE baseline data set, a comprehensive cohort of US children and adolescents with Pompe disease.

PURPOSE: To characterize clinical characteristics and genotypes of patients in the ADVANCE study of 4000 L-scale alglucosidase alfa (NCT01526785), the largest prospective United States Pompe disease cohort to date. METHODS: Patients aged ≥1 year with confirmed Pompe disease previously receiving 160 L alglucosidase alfa were eligible. GAA genotypes were determined before/at enrollment. Baseline assessments included histories/physical exams, Gross Motor Function Measure-88 (GMFM-88), pulmonary function tests, and cardiac assessments. RESULTS: Of 113 enrollees (60 male/53 female) aged 1-18 years, 87 had infantile-onset Pompe disease (IOPD) and 26 late-onset (LOPD). One hundred eight enrollees with GAA genotypes had 215 pathogenic variants (220 including combinations): 118 missense (4 combinations), 23 splice, 35 nonsense, 34 insertions/deletions, 9 duplications (1 combination), 6 other; c.2560C>T (n = 23), c.-32-13T>G (n = 13), and c.525delT (n = 12) were most common. Four patients had previously unpublished variants, and 14/83 (17%) genotyped IOPD patients were cross-reactive immunological material-negative. All IOPD and 6/26 LOPD patients had cardiac involvement, all without c.-32-13T>G. Thirty-two (26 IOPD, 6 LOPD) were invasively ventilated. GMFM-88 total %scores (mean ± SD, median, range): overall 46.3 ± 33.0% (47.9%, 0.0-100.0%), IOPD 41.6 ± 31.64% (38.9%, 0.0-99.7%), LOPD: 61.8 ± 33.2 (70.9%, 0.0-100.0%). CONCLUSION: ADVANCE, a uniformly assessed cohort comprising most US children and adolescents with treated Pompe disease, expands understanding of the phenotype and observed variants in the United States.

White matter lesions in treated late onset Pompe disease are not different to matched controls.

INTRODUCTION: Genetic deficiency of α-1,4-glucosidase leads to multi-systemic glycogen storage and causes muscular disorder known as classic infantile Pompe disease (CIOPD) and late onset Pompe disease (LOPD). Treatment with recombinant human alglucosidase alfa is available as enzyme replacement therapy (ERT). Recently progressive white matter lesions (WML) have been observed as a new phenotype in CIOPD patients on treatment with ERT. OBJECTIVE: To investigate the impact of disease and ERT for the development of WML in LOPD. METHODS: WML were analysed in 19 treated LOPD patients and compared with findings of 38 matched controls. RESULTS: Patients median age was 54.4 years (range 19 to 82 years) with median disease duration of 7 years (range 2 to 40 years). Median ERT duration was 63 months (range 9 to 135 months). Grading of WML by Fazekas Score was not different in LOPD patients and controls: Mean of total Fazekas score in LOPD was 2.42 ±â€¯2.40 and in controls 1.60 ±â€¯2.64; p = 0.68. Also volume of WML was similar in patients and controls (mean 5.27 ml ±â€¯5.88 and 7.89 ml ±â€¯11.40 respectively, p = 0.35). Total Fazekas grade correlated directly with the age in LOPD patients (r = 0.60; p = 0.007) and in controls (r = 0.32; p = 0.04). There was a negative correlation of ERT duration and total Fazekas grade (r = -0.41; p = 0.04). CONCLUSION: The study suggests that WML in LOPD mainly result from concomitant cerebrovascular risk factors rather than from the Pompe disease itself.

Real-world outcomes from a series of patients with late onset Pompe disease who switched from alglucosidase alfa to avalglucosidase alfa.

Introduction: Pompe disease is an inherited, progressive neuromuscular disorder caused by deficiency of lysosomal acid α-glucosidase and accumulation of glycogen in tissues, resulting in cellular dysfunction, muscle damage, and functional disabilities. Enzyme replacement therapy with alglucosidase alfa (Myozyme/Lumizyme) has led to better outcomes, but many patients have plateaued or declined despite treatment. The second-generation ERT avalglucosidase alfa (Nexviazyme) was designed to have enhanced cellular uptake via the conjugation of additional bis-mannose-6-phosphate residues. There have been trials comparing the efficacy of alglucosidase and avalglucosidase, but there remains a need for more real-world data on patients who switched from alglucosidase to avalglucosidase. Methods: A chart review was conducted on n = 15 patients with late-onset Pompe disease followed at a single center who switched from alglucosidase to avalglucosidase and continued for at least 6 months. Results: A total of n = 8/15 patients received alglucosidase for more than 3 years prior to switching, and n = 7/15 received it for more than 5 years prior to switching. There were statistically significant improvements in CK, Hex4, and AST with mean differences of -104.8 U/L, -3.0 mmol/molCr, and -14.7 U/L, respectively, post-switch. 6-Minute Walk Test; comfortable gait speed; Gait, Stairs, Gower, Chair; and Quick Motor Function Test scores improved or stabilized in most patients post-switch (n = 8/12, n = 11/12, n = 9/12, n =7/11, respectively). Of n = 7 patients with pulmonary function testing, n = 4/7 had improved upright FVC. Patient-reported outcomes revealed improvements in dyspnea (n = 4/4), physical function (n = 3/4), fatigue (n = 2/3), and lower back pain (n = 3/3). Avalglucosidase was well tolerated without infusion-associated reactions, and all n = 7 patients on home infusions continued receiving ERT at home. Anti-drug antibodies were seen in n = 9/10 of patients on alglucosidase and n = 8/13 of those on avalglucosidase, with titers below 12,800 in a majority of patients. We also present the first outcome data for a patient with LOPD who is non-ambulatory and a full-time wheelchair user; she demonstrated meaningful improvements in quality of life and motor function with the switch. Discussion: In summary, improved outcomes were seen in most patients, with a subset whose decline persisted. This study presents evidence that switching from alglucosidase to avalglucosidase may be associated with improved outcomes in certain patients with LOPD.

Clinical manifestations and acid alpha-glucosidase mutation characterisation of a cohort of patients with late-onset Pompe disease in eastern China.

BACKGROUND: Pompe disease is a rare, progressive, and life-threatening autosomal recessive disorder. In its late-onset form, the disease is primarily characterised by mild progressive proximal limb and respiratory muscle weakness. Mutations in the acid alpha-glucosidase (GAA) gene cause lysosomal enzyme GAA to be significantly reduced or missing altogether, for which supplementation can be given through enzyme replacement therapy. METHODS: Fourteen patients diagnosed with late-onset Pompe disease (LOPD) in the First Affiliated Hospital of Nanjing Medical University from 2017 to 2021 were enrolled. GAA activity was measured based on enzymatic activity in dried blood spots, and next-generation sequencing was used to detect mutations in the GAA gene. The impacts of novel missense variants were determined by five different prediction algorithms. The structural figures of novel variants and their wide types were processed with PyMOL. RESULTS: The study included 14 patients with LOPD (male-to-female ratio, 1:1) from eastern China. The median age at symptom onset and diagnosis was 15.0 years (7-36 years) and 21.5 years (8-47 years), respectively. The median diagnostic delay from onset was 3.0 years (0-22 years). Proximal muscle weakness was the first prominent symptom in 8 patients, while the other 6 patients experienced respiratory failure, chest congestion and asthma, and scoliosis. The most frequent mutation of the GAA gene was c.2238G>C (p.W746C), which was observed at an allele frequency of 14.3% (4/28) and in 28.6% of patients (4/14). Four novel variants potentially related to the pathogenicity of LOPD were found: c.1299G>C (p.Q433H), c.1409A>G (p.N470S), c.2242delG (p.E748Rfs*16), and c.2832delA (p.E945Sfs*78). CONCLUSIONS: The c.2238G>C (p.W746C) mutation was the most common mutation in 14 patients with LOPD from eastern China. This study has identified four novel variants in patients with LOPD. Predicting the pathogenicity of these novel variants may increase the understanding of the genetic mutation spectrum in LOPD. Our findings may also improve recognition of the characteristics of Chinese patients with LOPD.

Regional variation of thigh muscle fat infiltration in patients with neuromuscular diseases compared to healthy controls.

BACKGROUND: Chemical shift encoding-based water-fat magnetic resonance imaging (CSE-MRI) measures a quantitative biomarker: the proton density fat fraction (PDFF). The aim was to assess regional and proximo-distal PDFF variations at the thigh in patients with myotonic dystrophy type 2 (DM2), limb-girdle muscular dystrophy type 2A (LGMD2A), and late-onset Pompe disease (LOPD) as compared to healthy controls. METHODS: Seven patients (n=2 DM2, n=2 LGMD2A, n=3 LOPD) and 20 controls were recruited. A 3D-spoiled gradient echo sequence was used to scan the thigh musculature. Muscles were manually segmented to generate mean muscle PDFF. RESULTS: In all three disease entities, there was an increase in muscle fat replacement compared to healthy controls. However, within each disease group, there were patients with a shorter time since symptom onset that only showed mild PDFF elevation (range, 10% to 20%) compared to controls (P≤0.05), whereas patients with a longer period since symptom onset showed a more severe grade of fat replacement with a range of 50% to 70% (P<0.01). Increased PDFF of around 5% was observed for vastus medialis, semimembranosus and gracilis muscles in advanced compared to early DM2. LGMD2A_1 showed an early disease stage with predominantly mild PDFF elevations over all muscles and levels (10.9%±7.1%) compared to controls. The quadriceps, gracilis and biceps femoris muscles showed the highest difference between LGMD2A_1 with 5 years since symptom onset (average PDFF 11.1%±6.9%) compared to LGMD2A_2 with 32 years since symptom onset (average PDFF 66.3%±6.3%). For LOPD patients, overall PDFF elevations were observed in all major hip flexors and extensors (range, 25.8% to 30.8%) compared to controls (range, 1.7% to 2.3%, P<0.05). Proximal-to-distal PDFF highly varied within and between diseases and within controls. The intra-reader reliability was high (reproducibility coefficient ≤2.19%). CONCLUSIONS: By quantitatively measuring muscle fat infiltration at the thigh, we identified candidate muscles for disease monitoring due to their gradual PDFF elevation with longer disease duration. Regional variation between proximal, central, and distal muscle PDFF was high and is important to consider when performing longitudinal MRI follow-ups in the clinical setting or in longitudinal studies.

Safety and efficacy of short- and long-term inspiratory muscle training in late-onset Pompe disease (LOPD): a pilot study.

BACKGROUND: In patients with late-onset Pompe disease, progressive respiratory muscle weakness with predominantly diaphragmatic involvement is a frequent finding at later stages of the disease. Respiratory muscle training (RMT) is an established therapy option for patients with several neuromuscular disorders including Duchenne muscular dystrophy. Forced voluntary muscle contractions of inspiration and/or expiration muscles enhance ventilation by increasing respiratory coordination, endurance, and strength. Efficacy of RMT in LOPD is rarely examined, and the clinical studies performed are difficult to compare because of different training programs and protocols. This impedes a useful statement and recommendation about the safety and efficacy of respiratory muscle training. METHODS: We conducted a monocentric unblinded single-arm pilot study in patients with LOPD to evaluate the safety and efficacy of inspiratory muscle training (IMT). The primary objective was to determine the efficacy of a 6-week repetitive IMT with a gradual increase of inspiratory resistance, measured by MIP (maximum inspiratory pressure) in the upright position. For statistical analysis, we used an A-B-C single subject design. The 6-week training-period A was followed by a 6-week non-training period B and an optional training period of 40 weeks in period C. The total study duration for the periods A, B and C was 52 weeks. Throughout the study, spirometry assessments (FCV, FEV1) and measurements of respiratory strength (MIP, MEP) were performed at defined time points, as well as capillary oximetry and capnometry, motor function test and patient's questionnaires for quality of life and dyspnea, measured by St. George's Respiratory Questionnaire (SGRQ) and MMRC-Dyspnea scale. For the cross-sectional comparison, a paired two-sided t test, and for the longitudinal comparison, a two-sample, two-sided t test were used. When data were not normally distributed, a Wilcoxon-Mann-Whitney test was added. Finally, the annual decline in FVC and FEV1 before and after IMT was compared. FINDINGS: 11 subjects were included in this pilot study. Overall, IMT was well tolerated. In four subjects, a total of six adverse events related to the study procedures were noticed. Training compliance was excellent in the first weeks of training, but declined continuously in the extension period. There was a significant increase in our primary outcome measure MIP within the 6-week period of frequent IMT with a mean of 15.7% (p =0.024; d =0.402). A significant increase was also seen after week 52 by a mean of + 26.4% (mean + 13.4 cmH2O, p =0.001, d =0.636). In the 6-week non-training interim-period (period B), the values remained stable, and there was no clinically meaningful decline in secondary outcome measures. The increase in MIP did not have any effect on secondary outcome measures like spirometry tests (FVC, FEV1), capillary blood gas analysis, motor function tests, patient's perceived quality of life or any significant change in dyspnea score. CONCLUSIONS: Frequent IMT improves MIP and thereby stabilizes and decelerates the decline of the diaphragm strength. The gradual increase of inspiratory resistance is well tolerated without any increase of side effects, as long as IMT is supervised and resistance is individually adjusted to the patient's perceived grade of exhaustion. Although we could not detect a significant impact on secondary outcome measures, IMT should be offered to all LOPD patients, especially to those who demonstrate a progressive decline in respiratory muscle function or are unable to receive ERT.

Safety, tolerability, pharmacokinetics, pharmacodynamics, and exploratory efficacy of the novel enzyme replacement therapy avalglucosidase alfa (neoGAA) in treatment-naïve and alglucosidase alfa-treated patients with late-onset Pompe disease: A phase 1, open-label, multicenter, multinational, ascending dose study.

This multicenter/multinational, open-label, ascending-dose study (NCT01898364) evaluated safety, tolerability, pharmacokinetics, pharmacodynamics, and exploratory efficacy of repeat-dose avalglucosidase alfa (neoGAA), a second-generation, recombinant acid α-glucosidase replacement therapy, in late-onset Pompe disease (LOPD). Patients ≥18 years, alglucosidase alfa naïve (Naïve) or previously receiving alglucosidase alfa for ≥9 months (Switch), with baseline FVC ≥50% predicted and independently ambulatory, received every-other-week avalglucosidase alfa 5, 10, or 20 mg/kg over 24 weeks. 9/10 Naïve and 12/14 Switch patients completed the study. Avalglucosidase alfa was well-tolerated; no deaths/life-threatening serious adverse events (SAEs). One Naïve patient withdrew for study drug-related SAEs (respiratory distress/chest discomfort). Infusion-associated reactions (IARs) affected 8 patients. Most treatment-emergent AEs/IARs were non-serious with mild-to-moderate intensity. At screening, 5 Switch patients tested positive for anti-avalglucosidase alfa antibodies; on-treatment, 2 Switch and 9 Naïve patients seroconverted. Post-infusion, avalglucosidase alfa plasma concentrations declined monoexponentially (t1/2z∼1.0 h). AUC was 5-6 × higher in the 20 vs 5 mg/kg group. Pharmacokinetics were similar between Switch and Naïve groups and over time. Baseline quadriceps muscle glycogen was low (∼6%) in most patients, generally remaining unchanged thereafter. Exploratory efficacy parameters (pulmonary function/functional capacity) generally remained stable or improved. Avalglucosidase alfa's well-tolerated safety profile and exploratory efficacy results support further avalglucosidase alfa development.

Targeted gene panel screening is an effective tool to identify undiagnosed late onset Pompe disease.

Mutations in the GAA gene may cause a late onset Pompe disease presenting with proximal weakness without the characteristic muscle pathology, and therefore a test for GAA activity is the first tier analysis in all undiagnosed patients with hyperCKemia and/or limb-girdle muscular weakness. By using MotorPlex, a targeted gene panel for next generation sequencing, we analyzed GAA and other muscle disease-genes in a large cohort of undiagnosed patients with suspected inherited skeletal muscle disorders (n = 504). In this cohort, 275 patients presented with limb-girdle phenotype and/or an isolated hyperCKemia. Mutational analysis identified GAA mutations in ten patients. Further seven affected relatives were identified by segregation studies. All the patients carried the common GAA mutation c.-32-13T >G and a second, previously reported mutation. In the subcohort of 275 patients with proximal muscle weakness and/or hyperCKemia, we identified late-onset Pompe disease in 10 patients. The clinical overlap between Pompe disease and LGMDs or other skeletal muscle disorders suggests that GAA and the genes causing a metabolic myopathy should be analyzed in all the gene panels used for testing neuromuscular patients. However, enzymatic tests are essential for the interpretation and validation of genetic results.

Decreased outlet angle of the superior cerebellar artery as indicator for dolichoectasia in late onset Pompe disease.

BACKGROUND: Lysosomal α-glucosidase deficiency (Pompe disease) not only leads to glycogen accumulation in skeletal muscle, but also in the cerebral arteries. Dolichoectasia of the basilar artery (BA) has been frequently reported. Therefore progression of BA dolichoectasia in late onset Pompe patients (LOPD) was studied. METHODS: BA length, diameter and volume, and cerebral lesions were analysed by MRI/TOF-MR angiography or CT/CT angiography in 20 LOPD patients and 40 controls matching in age, sex- and cardiovascular risk factors. The height of BA bifurcation was assessed semi-quantitatively using the Smoker's criteria and quantitatively by measuring the outlet angle of the superior cerebellar artery (SUCA). Nine patients were followed over 5 years. RESULTS: The height of the BA bifurcation was abnormal in 12/20 (60%) LOPD patients and in 12/40 (30%) matched controls. The SUCA outlet angle was reduced in LOPD patients compared to controls (127 ± 33° vs. 156 ± 32°, p = 0.0024). The diameter, length and volume of the BA were significantly increased in LOPD patients compared to controls. 12/20 (60%) LOPD patients and 27/40 (68%) controls presented white matter lesions. During 5 years 2/9 LOPD patients developed an abnormal height of BA bifurcation according to the Smoker's criteria and in all patients the SUCA outlet angle decreased (138 ± 34° vs. 128 ± 32°, p = 0.019). One patient with prominent basilar dolichoectasia experienced a thalamic hemorrhage. CONCLUSION: Pompe disease is associated with BA dilation, elongation and elevated bifurcation height of the BA which might result in cerebrovascular complications. The SUCA outlet angle seems to be useful for monitoring the progression of BA dolichoectasia.

Survival and long-term outcomes in late-onset Pompe disease following alglucosidase alfa treatment: a systematic review and meta-analysis.

A number of studies have assessed the efficacy of alglucosidase alfa as an enzyme replacement therapy (ERT) on motor and respiratory endpoints in patients with late-onset Pompe disease (LOPD). A previous review evaluated the clinical efficacy and safety of alglucosidase alfa; however, it is difficult to draw inferences from individual studies due to small patient populations, particularly in evaluating the benefit on survival. To evaluate the current evidence on the long-term efficacy of alglucosidase alfa with regard to survival, motor, and respiratory function in patients with LOPD in relation to the natural progression of the disease, a new systematic literature review was performed identifying studies that assessed either mortality, percent predicted forced vital capacity (% FVC), or the 6-min walk test (6MWT) among treated and untreated LOPD patients. Patient overlap was avoided by removing smaller studies or ensuring the use of only one conflicting study per outcome. Mortality was modeled using Poisson models for each treatment group. Outcomes were modeled using first- and second-order fractional polynomial meta-analysis with fixed- and random-effects. Meta-regression was used to explore sources of heterogeneity. Twenty-two publications pertaining to 19 studies/trials were selected, including 438 patients when accounting for overlaps, with the average study duration being 45.7 months. Patients treated with alglucosidase alfa in these studies had a nearly five-fold lower mortality rate than untreated patients (rate ratio: 0.21; 95 % credible interval: 0.11, 0.41). On average, % FVC declined consistently among untreated patients, including a 2.3 % decline after 12 months follow-up and 6.2 % decline after 48 months. This is in contrast to alglucosidase alfa-treated patients, who, on average, improved rapidly, with an increase of 1.4 % FVC after 2 months, followed by a slow regression back to baseline over a three-year period. Nonetheless, the relative difference between those treated and not grew over time, from 4.5 % FVC after 12 months to 6 % FVC after 48 months. In the 6MWT, alglucosidase alfa-treated patients on average had the largest improvement over the first 20 months of treatment of approximately 50 meters increase over baseline, with its substantial stabilization in the following years. By comparison, untreated patients do not show 6MWT improvement over time. Alglucosidase alfa has a beneficial effect in LOPD patients as demonstrated by improvements in survival and ambulation maintained over time, as well as prevention of deterioration in respiratory function.