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

Clinical modeling of motor function to predict treatment efficacy and enable in silico treatment comparisons in infantile-onset Pompe disease

Infantile-onset Pompe disease (IOPD) is a rare, deadly, quickly-progressing degenerative disease. Even with life-sustaining treatment (e.g., alglucosidase alfa [ALGLU]), many patients experience continued motor impairment. The Mini-COMET trial evaluated avalglucosidase alfa (AVAL) versus ALGLU on motor and other outcomes in IOPD. However, treatment groups were imbalanced at baseline and the trial was not powered to directly compare treatments. To supplement this limited data, we developed a modeling and simulation approach to compare AVAL versus ALGLU head-to-head in in silico (i.e., computer-simulated) trials. We first developed a longitudinal clinical model to establish the relationship between changes in motor function and changes in urinary hexose tetrasaccharide (uHex4), an established biomarker in IOPD. This model was based on pooled data from Mini-COMET (n = 21) and COMET trials (n = 100 patients with late-onset Pompe disease, LOPD). We then conducted in silico trials mimicking Mini-COMET. Simulated trials were informed by motor data generated from the clinical model and uHex4 profiles simulated in a quantitative systems pharmacology model. The virtual IOPD population was based on observed Mini-COMET baseline characteristics but engineered to have well-balanced baseline characteristics across treatment cohorts. In silico trials showed that patients with IOPD would have the greatest improvements in motor function with AVAL 40 mg/kg every other week (Q2W), suboptimal improvement with ALGLU 40 mg/kg Q2W, and no improvement with ALGLU 20 mg/kg Q2W. This study provides information on the relative efficacy of IOPD treatments and mitigates the confounding effects of imbalanced treatment cohorts. Our approach could also be applied in other rare diseases.

Home infusion experience in patients with Pompe disease receiving avalglucosidase alfa during three clinical trials

During three previously reported clinical trials of avalglucosidase alfa in patients with Pompe disease, 17 out of 142 participants were considered by the investigators to be appropriate candidates for home infusion. During their respective trials, these participants received a total of 419 avalglucosidase alfa infusions at home under healthcare professional supervision. They were clinically stable with no history of moderate or severe infusion-associated reactions within at least 12 months prior to starting home infusions. As of February 25, 2022, the 15 participants with late-onset Pompe disease (LOPD) had received between 2 and 48 home infusions and the 2 participants with infantile-onset Pompe disease (IOPD) had received 19 and 20 infusions. Adverse events occurred in 8 (53 %) participants with LOPD and neither of the participants with IOPD. Seven participants with LOPD had a total of 15 non-treatment-related, non-serious adverse events. One participant with LOPD experienced infusion-associated reactions of eyelid edema and flushing during the first home infusion; both were non-serious adverse events classified as grade 1 (mild). Home infusion was later resumed for this participant. Among LOPD participants, event rates for home infusions were comparable to those for clinic infusions: overall adverse events (0.028 vs 0.039 participants with events/infusion, respectively) and adverse events classified as infusion-associated reactions (0.003 vs. 0.006, respectively). No medication errors occurred during home infusion. These data suggest that infusion of avalglucosidase alfa at home is feasible and does not compromise safety for patients who have not experienced an infusion-associated reaction during the preceding 12 months of infusions in a clinical setting. Evaluation of real-world experience with avalglucosidase alfa home infusion in countries where it is already approved is ongoing.

Cipaglucosidase alfa plus miglustat: linking mechanism of action to clinical outcomes in late-onset Pompe disease

Enzyme replacement therapy (ERT) is the only approved disease-modifying treatment modality for Pompe disease, a rare, inherited metabolic disorder caused by a deficiency in the acid α-glucosidase (GAA) enzyme that catabolizes lysosomal glycogen. First-generation recombinant human GAA (rhGAA) ERT (alglucosidase alfa) can slow the progressive muscle degeneration characteristic of the disease. Still, most patients experience diminished efficacy over time, possibly because of poor uptake into target tissues. Next-generation ERTs aim to address this problem by increasing bis-phosphorylated high mannose (bis-M6P) N-glycans on rhGAA as these moieties have sufficiently high receptor binding affinity at the resultant low interstitial enzyme concentrations after dosing to drive uptake by the cation-independent mannose 6-phosphate receptor on target cells. However, some approaches introduce bis-M6P onto rhGAA via non-natural linkages that cannot be hydrolyzed by natural human enzymes and thus inhibit the endolysosomal glycan trimming necessary for complete enzyme activation after cell uptake. Furthermore, all rhGAA ERTs face potential inactivation during intravenous delivery (and subsequent non-productive clearance) as GAA is an acid hydrolase that is rapidly denatured in the near-neutral pH of the blood. One new therapy, cipaglucosidase alfa plus miglustat, is hypothesized to address these challenges by combining an enzyme enriched with naturally occurring bis-M6P N-glycans with a small-molecule stabilizer. Here, we investigate this hypothesis by analyzing published and new data related to the mechanism of action of the enzyme and stabilizer molecule. Based on an extensive collection of in vitro, preclinical, and clinical data, we conclude that cipaglucosidase alfa plus miglustat successfully addresses each of these challenges to offer meaningful advantages in terms of pharmacokinetic exposure, target-cell uptake, endolysosomal processing, and clinical benefit.

Comparing the efficacy of cipaglucosidase alfa plus miglustat with other enzyme replacement therapies for late-onset Pompe disease: a network meta-analysis utilizing patient-level and aggregate data

Aim: Late-onset Pompe disease is characterized by progressive loss of muscular and respiratory function. Until recently, standard of care was enzyme replacement therapy (ERT) with alglucosidase alfa. Second-generation ERTs avalglucosidase alfa (aval) and cipaglucosidase alfa with miglustat (cipa+mig) are now available. Without head-to-head trials comparing aval with cipa+mig, an indirect treatment comparison is informative and timely for understanding potential clinical differentiation. Materials & methods: A systematic literature review was performed to identify relevant studies on cipa+mig and aval. Using patient-level and aggregate published data from randomized controlled trials (RCTs) and phase I/II and open-label extension (OLE) trials, a multi-level network meta-regression was conducted, adjusting for various baseline covariates, including previous ERT duration, to obtain relative effect estimates on 6-minute walk distance (6MWD, meters [m]) and forced vital capacity (FVC, % predicted [pp]). Analyses of two networks were conducted: Network A, including only RCTs, and network B, additionally including single-arm OLE and phase I/II studies. Results: Network B (full evidence analysis) showed that cipa+mig was associated with a relative increase in 6MWD (mean difference 28.93 m, 95% credible interval [8.26-50.11 m]; Bayesian probability 99.7%) and FVC (2.88 pp [1.07-4.71 pp]; >99.9%) compared with aval. The comparison between cipa+mig and aval became more favorable for cipa+mig with increasing previous ERT duration for both end points. Analysis of network A showed that cipa+mig was associated with a relative decrease in 6MWD (-10.02 m [-23.62 to 4.00 m]; 91.8%) and FVC (-1.45 pp [-3.01 to 0.07 pp]; 96.8%) compared with aval. Conclusion: Cipa+mig showed a favorable effect versus aval when all available evidence was used in the analysis.

Comparative study on incorporation of three recombinant human α-galactosidase A drugs (agalsidases) into cultured fibroblasts and organs/tissues of Fabry mice

Enzyme replacement therapy (ERT) with recombinant human α-galactosidase A (α-Gal A) drugs (agalsidases) has been successfully used for treatment of Fabry disease, and three kinds of agalsidases are now available in Japan. To compare the biochemical characteristics of these drugs, especially focusing on their incorporation into cultured fibroblasts and organs/tissues of Fabry mice, we performed in vitro, cell, and animal experiments. The results revealed that there were no differences in the kinetic parameters and enzyme activity between these agalsidases. But their affinity for domain 9 of cation-independent mannose 6-phosphate receptor (CI-M6PR), which exists in various cells, was higher in the order: agalsidase beta biosimilar 1 (agalsidase beta BS) > agalsidase beta > agalsidase alfa, which almost coincided with the experimental results regarding the efficiency of their incorporation into cultured fibroblasts derived from a Fabry mouse. The results of animal experiments using Fabry mice revealed that the incorporation of the agalsidases into the kidneys and heart, where CI-M6PRs are widely distributed, was efficient in the order: agalsidase beta/agalsidase beta BS > agalsidase alfa, which reflected the degree of reduction of glycosphingolipids accumulated in the organs/tissues. On the other hand, no differences in the efficiency of their uptake or reduction of the accumulated substances were observed in the liver, probably due to asialoglycoprotein receptors expressed on the surface of hepatocytes. This information will be useful for making a suitable ERT plan for individual Fabry patients with various backgrounds and for developing new ERT drugs in the future.

Efficacy of avalglucosidase alfa on forced vital capacity percent predicted in treatment-naïve patients with late-onset Pompe disease: A pooled analysis of clinical trials

Background

The efficacy of avalglucosidase alfa (AVA) versus alglucosidase alfa (ALG) on forced vital capacity percent predicted (FVCpp) in patients with late-onset Pompe disease (LOPD) has been assessed in the Phase 3 COMET trial (NCT02782741). Due to the rarity of LOPD and thus small sample size in COMET, additional data were analyzed to gain further insights into the efficacy of AVA versus ALG.

Methods

Data from treatment-naive patients with LOPD were pooled from COMET and Phase 1/2 NEO1/NEO-EXT (NCT01898364/NCT02032524) trials for patients treated with AVA, and Phase 3 LOTS trial (NCT00158600) for patients treated with ALG. Regression analyses using mixed models with repeated measures consistent with those pre-specified in COMET were performed post-hoc. Analyses were adjusted for trials and differences in baseline characteristics. Four models were developed: Model 1 considered all trials; Model 2 included Phase 3 trials; Model 3 included Phase 3 trials and was adjusted for baseline ventilation use; Model 4 included COMET and NEO1/NEO-EXT (i.e., AVA trials only).

Results

Overall, 100 randomized patients from COMET (AVA, n = 51, ALG, n = 49), 60 from LOTS (ALG arm only), and three patients from NEO1/NEO-EXT (who received open-label AVA only) were considered for analysis. Mean age at enrollment was similar across trials (45.3-50.3 years); however, patients from LOTS had a longer mean duration of disease versus COMET and NEO1/NEO-EXT trials (9.0 years and 0.5-2.2 years, respectively) and younger mean age at diagnosis (36.2 years and 44.7-48.6 years, respectively). Least squares mean (95% confidence interval) improvement from baseline in FVCpp at Week 49-52 for AVA versus ALG was 2.43 (-0.13; 4.99) for COMET (n = 98); 2.31 (0.06; 4.57) for Model 1 (n = 160); 2.43 (0.21; 4.65) for Model 2 (n = 157); 2.80 (0.54; 5.05) for Model 3 (n = 154); and 2.27 (-0.30; 4.45) for Model 4 (n = 101).

Conclusions

Models 1 to 3, which had an increased sample size versus COMET, demonstrated a nominally significant effect on FVCpp favoring AVA versus ALG after 1 year of treatment, consistent with results from COMET.

Neurological glycogen storage diseases and emerging therapeutics

Glycogen storage diseases (GSDs) comprise a group of inherited metabolic disorders characterized by defects in glycogen metabolism, leading to abnormal glycogen accumulation in multiple tissues, most notably affecting the liver, skeletal muscle, and heart. Recent findings have uncovered the importance of glycogen metabolism in the brain, sustaining a myriad of physiological functions and linking its perturbation to central nervous system (CNS) pathology. This link resulted in classification of neurological-GSDs (n-GSDs), a group of diseases with shared deficits in neurological glycogen metabolism. The n-GSD patients exhibit a spectrum of clinical presentations with common etiology while requiring tailored therapeutic approaches from the traditional GSDs. Recent research has elucidated the genetic and biochemical mechanisms and pathophysiological basis underlying different n-GSDs. Further, the last decade has witnessed some promising developments in novel therapeutic approaches, including enzyme replacement therapy (ERT), substrate reduction therapy (SRT), small molecule drugs, and gene therapy targeting key aspects of glycogen metabolism in specific n-GSDs. This preclinical progress has generated noticeable success in potentially modifying disease course and improving clinical outcomes in patients. Herein, we provide an overview of current perspectives on n-GSDs, emphasizing recent advances in understanding their molecular basis, therapeutic developments, underscore key challenges and the need to deepen our understanding of n-GSDs pathogenesis to develop better therapeutic strategies that could offer improved treatment and sustainable benefits to the patients.

Changes in forced vital capacity over ≤ 13 years among patients with late-onset Pompe disease treated with alglucosidase alfa: new modeling of real-world data from the Pompe Registry

BACKGROUND

Chronic respiratory insufficiency from progressive muscle weakness causes morbidity and mortality in late-onset Pompe disease (LOPD). Previous Pompe Registry (NCT00231400) analyses for ≤ 5 years' alglucosidase alfa treatment showed a single linear time trend of stable forced vital capacity (FVC) % predicted.

METHODS

To assess longer term Pompe Registry data, piecewise linear mixed model regression analyses estimated FVC% predicted trajectories in invasive-ventilator-free patients with LOPD aged ≥ 5 years. We estimated annual FVC change 0-6 months, > 6 months-5 years, and > 5-13 years from treatment initiation, adjusting for baseline age, sex, and non-invasive ventilation.

FINDINGS

Among 485 patients (4612 FVC measurements; 8.3 years median follow-up), median ages at symptom onset, diagnosis, and alglucosidase alfa initiation were 34.3, 41.1, and 44.9 years, respectively. FVC% increased during the first 6 months' treatment (slope 1.83%/year; 95% confidence interval: 0.66, 3.01; P = 0.0023), then modestly declined -0.54%/year (-0.79, -0.30; P < 0.0001) during > 6 months-5 years, and -1.00%/year (-1.36, -0.63; P < 0.0001) during > 5-13 years. The latter two periods' slopes were not significantly different from each other (Pdifference = 0.0654) and were less steep than published natural history slopes (-1% to -4.6%/year). Estimated individual slopes were ≥ 0%/year in 96.1%, 30.3%, and 13.2% of patients during the 0-6 month, > 6 month-5 year, and > 5-13 year periods, respectively.

CONCLUSION

These real-world data indicate an alglucosidase alfa benefit on FVC trajectory that persists at least 13 years compared with published natural history data. Nevertheless, unmet need remains since most individuals demonstrate lung function decline 5 years after initiating treatment. Whether altered FVC trajectory impacts respiratory failure incidence remains undetermined.

TRIAL REGISTRATION

This study was registered (NCT00231400) on ClinicalTrials.gov on September 30, 2005, retrospectively registered.

Lung Diseases and Rare Disorders: Is It a Lysosomal Storage Disease? Differential Diagnosis, Pathogenetic Mechanisms and Management

Pulmonologists may be involved in managing pulmonary diseases in children with complex clinical pictures without a diagnosis. Moreover, they are routinely involved in the multidisciplinary care of children with rare diseases, at baseline and during follow-up, for lung function monitoring. Lysosomal storage diseases (LSDs) are a group of genetic diseases characterised by a specific lysosomal enzyme deficiency. Despite varying pathogen and organ involvement, they are linked by the pathological accumulation of exceeding substrates, leading to cellular toxicity and subsequent organ damage. Less severe forms of LSDs can manifest during childhood or later in life, sometimes being underdiagnosed. Respiratory impairment may stem from different pathogenetic mechanisms, depending on substrate storage in bones, with skeletal deformity and restrictive pattern, in bronchi, with obstructive pattern, in lung interstitium, with altered alveolar gas exchange, and in muscles, with hypotonia. This narrative review aims to outline different pulmonary clinical findings and a diagnostic approach based on key elements for differential diagnosis in some treatable LSDs like Gaucher disease, Acid Sphingomyelinase deficiency, Pompe disease and Mucopolysaccharidosis. Alongside their respiratory clinical aspects, which might overlap, we will describe radiological findings, lung functional patterns and associated symptoms to guide pediatric pulmonologists in differential diagnosis. The second part of the paper will address follow-up and management specifics. Recent evidence suggests that new therapeutic strategies play a substantial role in preventing lung involvement in early-treated patients and enhancing lung function and radiological signs in others. Timely diagnosis, driven by clinical suspicion and diagnostic workup, can help in treating LSDs effectively.

Long-term safety and efficacy of cipaglucosidase alfa plus miglustat in individuals living with Pompe disease: an open-label phase I/II study (ATB200-02)

Cipaglucosidase alfa plus miglustat (cipa + mig) is a novel, two-component therapy for Pompe disease. We report data from the Phase I/II ATB200-02 study for up to 48 months of treatment. Four adult cohorts, including one non-ambulatory ERT-experienced (n = 6) and three ambulatory cohorts, (two enzyme replacement therapy [ERT]-experienced cohorts [2-6 years (n = 11) and ≥ 7 years (n = 6)]), one ERT-naïve cohort (n = 6), received 20 mg/kg intravenous-infused cipa plus 260 mg oral mig biweekly. Change from baseline (CFBL) for multiple efficacy endpoints at 12, 24, 36, and 48 months, pharmacodynamics, pharmacokinetics, safety, and immunogenicity data were assessed. Six-minute walking distance (% predicted) improved at 12, 24, 36, and 48 months: pooled ambulatory ERT-experienced cohorts, mean(± standard deviation [SD]) CFBL: 6.1(± 7.84), n = 16; 5.4(± 10.56), n = 13; 3.4(± 14.66), n = 12; 5.9(± 17.36), n = 9, respectively; ERT-naïve cohort: 10.7(± 3.93), n = 6; 11.0(± 5.06), n = 6; 9.0(± 7.98), n = 5; 11.7(± 7.69), n = 4, respectively. Percent predicted forced vital capacity was generally stable in ERT-experienced cohorts, mean(± SD) CFBL - 1.2(± 5.95), n = 16; 1.0(± 7.96), n = 13; - 0.3(± 6.68), n = 10; 1.0(± 6.42), n = 6, respectively, and improved in the ERT-naïve cohort: 3.2(± 8.42), n = 6; 4.7(± 5.09), n = 6; 6.2(± 3.35), n = 5; 8.3(± 4.50), n = 4, respectively. Over 48 months, CK and Hex4 biomarkers improved in ambulatory cohorts. Overall, cipa + mig was well tolerated with a safety profile like alglucosidase alfa. ATB200-02 results show the potential benefits of cipa + mig as a long-term treatment option for Pompe disease. Trial registration number: NCT02675465 January 26, 2016.

Evaluating avalglucosidase alfa for the management of late-onset Pompe disease

INTRODUCTION

Glycogenosis type II (GSDII) is a rare autosomal disorder that is caused by the deficiency of alpha-glucosidase, a lysosomal enzyme that hydrolyzes glycogen to glucose. Autophagy dysregulation plays a critical role. Importantly, since 2006, both patients with infantile (classic Pompe disease) and adult GSDII (late-onset Pompe disease or LOPD) have been treated with enzyme replacement therapy (ERT). To support this use, several double-blind and observational studies including large cohorts of GSDII patients have been undertaken and have shown ERT to be effective in modifying the natural course of disease. Indeed, most LOPD cases improve in the first 20 months of treatment in a six-minute walk test (6MWT), while those who are untreated do not; instead, their response declines over time.

AREAS COVERED

The author reviews avalglucosidase alpha, a therapy approved by both the FDA and European regulatory agencies. Herein, the author considers the pathophysiological approaches such as the role of enzyme entry, autophagy, and the response to ERT treatment of motor and respiratory components.

EXPERT OPINION

There has been a notable drive toward the research of various aspects of this disease regarding the role of new enzyme penetration and immune adverse events. Consequently, avalglucosidase alpha might be a further step forward.

Real-world evidence study finds no new-onset diabetes or drug-related hyperglycemia in Pompe disease patients treated with avalglucosidase alfa

Avalglucosidase alfa therapy for Pompe disease is diluted in dextrose 5% solution in water (D5W) for infusion, which raises questions about the potential for hyperglycemia or worsening diabetes. Using United States insurance claims data, we assessed the impact of biweekly infusions on hyperglycemia, new-onset diabetes mellitus, insulin resistance, and prediabetes in patients with Pompe disease. After starting avalglucosidase alfa treatment, 1 of 26 patients had one claim for hyperglycemia, which was attributed to acute pancreatitis.

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.

Lysosomal Dysfunction: Connecting the Dots in the Landscape of Human Diseases

Lysosomes are the main organelles responsible for the degradation of macromolecules in eukaryotic cells. Beyond their fundamental role in degradation, lysosomes are involved in different physiological processes such as autophagy, nutrient sensing, and intracellular signaling. In some circumstances, lysosomal abnormalities underlie several human pathologies with different etiologies known as known as lysosomal storage disorders (LSDs). These disorders can result from deficiencies in primary lysosomal enzymes, dysfunction of lysosomal enzyme activators, alterations in modifiers that impact lysosomal function, or changes in membrane-associated proteins, among other factors. The clinical phenotype observed in affected patients hinges on the type and location of the accumulating substrate, influenced by genetic mutations and residual enzyme activity. In this context, the scientific community is dedicated to exploring potential therapeutic approaches, striving not only to extend lifespan but also to enhance the overall quality of life for individuals afflicted with LSDs. This review provides insights into lysosomal dysfunction from a molecular perspective, particularly in the context of human diseases, and highlights recent advancements and breakthroughs in this field.

The Importance of Early Treatment of Inherited Neuromuscular Conditions

There has been tremendous progress in treatment of neuromuscular diseases over the last 20 years, which has transformed the natural history of these severely debilitating conditions. Although the factors that determine the response to therapy are many and in some instance remain to be fully elucidated, early treatment clearly has a major impact on patient outcomes across a number of inherited neuromuscular conditions. To improve patient care and outcomes, clinicians should be aware of neuromuscular conditions that require prompt treatment initiation. This review describes data that underscore the importance of early treatment of children with inherited neuromuscular conditions with an emphasis on data resulting from newborn screening efforts.

Targeted protein degradation through site-specific antibody conjugation with mannose 6-phosphate glycan

Recent developments in targeted protein degradation have provided great opportunities to eliminating extracellular protein targets using potential therapies with unique mechanisms of action and pharmacology. Among them, Lysosome-Targeting Chimeras (LYTACs) acting through mannose 6-phosphate receptor (M6PR) have been shown to facilitate degradation of several soluble and membrane-associated proteins in lysosomes with high efficiency. Herein we have developed a novel site-specific antibody conjugation approach to generate antibody mannose 6-phosphate (M6P) conjugates. The method uses a high affinity synthetic M6P glycan, bisM6P, that is coupled to an Fc-engineered antibody NNAS. This mutant without any effector function was generated by switching the native glycosylation site from position 297 to 298 converting non-sialylated structures to highly sialylated N-glycans. The sialic acid of the glycans attached to Asn298 in the engineered antibody was selectively conjugated to bisM6P without chemoenzymatic modification, which is often used for site-specific antibody conjugation through glycans. The conjugate is mainly homogeneous by analysis using mass spectrometry, typically with one or two glycans coupled. The M6P-conjugated antibody against a protein of interest (POI) efficiently internalized targeted soluble proteins, such as human tumor necrosis factor (TNF), in both cancer cell lines and human immune cells, through the endo-lysosomal pathway as demonstrated by confocal microscopy and flow cytometry. TNF in cell culture media was significantly depleted after the cells were incubated with the M6P-conjugated antibody. TNF internalization is mediated through M6PR, and it is correlated well with cell surface expression of cation-independent M6PR (CI-MPR) in immune cells. A significant amount of CI-MPR remains on the cell surface, while internalized TNF is degraded in lysosomes. Thus, the antibody-M6P conjugate is highly efficient in inducing internalization and subsequent lysosome-mediated protein degradation. Our platform provides a unique method for producing biologics-based degraders that may be used to treat diseases through event-driven pharmacology, thereby addressing unmet medical needs.

Long-Term Outcome of Infantile Onset Pompe Disease Patients Treated with Enzyme Replacement Therapy - Data from a German-Austrian Cohort

BACKGROUND

Enzyme replacement therapy (ERT) with recombinant human alglucosidase alfa (rhGAA) was approved in Europe in 2006. Nevertheless, data on the long-term outcome of infantile onset Pompe disease (IOPD) patients at school age is still limited.

OBJECTIVE

We analyzed in detail cardiac, respiratory, motor, and cognitive function of 15 German-speaking patients aged 7 and older who started ERT at a median age of 5 months.

RESULTS

Starting dose was 20 mg/kg biweekly in 12 patients, 20 mg/kg weekly in 2, and 40 mg/kg weekly in one patient. CRIM-status was positive in 13 patients (86.7%) and negative or unknown in one patient each (6.7%). Three patients (20%) received immunomodulation. Median age at last assessment was 9.1 (7.0-19.5) years. At last follow-up 1 patient (6.7%) had mild cardiac hypertrophy, 6 (42.9%) had cardiac arrhythmias, and 7 (46.7%) required assisted ventilation. Seven patients (46.7%) achieved the ability to walk independently and 5 (33.3%) were still ambulatory at last follow-up. Six patients (40%) were able to sit without support, while the remaining 4 (26.7%) were tetraplegic. Eleven patients underwent cognitive testing (Culture Fair Intelligence Test), while 4 were unable to meet the requirements for cognitive testing. Intelligence quotients (IQs) ranged from normal (IQ 117, 102, 96, 94) in 4 patients (36.4%) to mild developmental delay (IQ 81) in one patient (9.1%) to intellectual disability (IQ 69, 63, 61, 3x <55) in 6 patients (54.5%). White matter abnormalities were present in 10 out of 12 cerebral MRIs from 7 patients.

CONCLUSION

Substantial motor, cardiac, respiratory, and cognitive deficits are frequent in IOPD long-term survivors who started ERT before 2016. The findings of this study can be valuable as comparative data when evaluating the impact of newer treatment strategies including higher enzyme dosage, immunomodulation, modified enzymes, or early start of treatment following newborn screening.

Population pharmacokinetic modeling and dosing simulation of avalglucosidase alfa for selecting alternative dosing regimen in pediatric patients with late-onset pompe disease

Avalglucosidase alfa (AVAL) was approved in the United States (2021) for patients with late-onset Pompe disease (LOPD), aged ≥ 1 year. In the present study, pharmacokinetic (PK) simulations were conducted to propose alternative dosing regimens for pediatric LOPD patients based on a bodyweight cut-off. Population PK (PopPK) analysis was performed using nonlinear mixed effect modeling approach on pooled data from three clinical trials with LOPD patients, and a phase 2 study (NCT03019406) with infantile-onset Pompe disease (IOPD: 1-12 years) patients. A total of 2257 concentration-time points from 91 patients (LOPD, n = 75; IOPD, n = 16) were included in the analysis. The model was bodyweight dependent allometric scaling with time varying bodyweight included on clearance and distribution volume. Simulations were performed for two dosing regimens (20 mg/kg or 40 mg/kg) with different bodyweight cut-off (25, 30, 35 and 40 kg) by generating virtual pediatric (1-17 years) and adult patients. Corresponding simulated individual exposures (maximal concentration, Cmax and area under the curve in the 2-week dosing interval, AUC2W), and distributions were calculated. It was found that dosing of 40 mg/kg and 20 mg/kg in pediatric patients < 30 kg and ≥ 30 kg, respectively, achieved similar AVAL exposure (based on AUC2W) to adult patients receiving 20 mg/kg. PK simulations conducted on the basis of this model provided supporting data for the currently approved US labelling for dosing adapted bodyweight in LOPD patients ≥ 1 year by USFDA.

Clinical and biochemical footprints of inherited metabolic diseases. XIII. Respiratory manifestations

At any age, respiratory manifestations are a major cause of increased morbidity and mortality of inherited metabolic diseases (IMDs). Type and severity are extremely variable, this depending on the type of the underlying disorder. Symptoms and signs originating from upper or lower airways and/or thoracic wall and/or respiratory muscles involvement can occur either at presentation or in the late clinical course. Acute respiratory symptoms can trigger metabolic decompensation which, in turn, makes airway symptoms worse, creating a vicious circle. We have identified 181 IMDs associated with various types of respiratory symptoms which were classified into seven groups according to the type of clinical manifestations affecting the respiratory system: (i) respiratory failure, (ii) restrictive lung disease, (iii) interstitial lung disease, (iv) lower airway disease, (v) upper airway obstruction, (vi) apnea, and (vii) other. We also provided a list of investigations to be performed based on the respiratory phenotypes and indicated the therapeutic strategies currently available for IMD-associated airway disease. This represents the thirteenth issue in a series of educational summaries providing a comprehensive and updated list of metabolic differential diagnoses according to system involvement.

Increasing Enzyme Mannose-6-Phosphate Levels but Not Miglustat Coadministration Enhances the Efficacy of Enzyme Replacement Therapy in Pompe Mice

Pompe disease is a rare glycogen storage disorder caused by a deficiency in the lysosomal enzyme acid α-glucosidase, which leads to muscle weakness, cardiac and respiratory failure, and early mortality. Alglucosidase alfa, a recombinant human acid α-glucosidase, was the first approved treatment of Pompe disease, but its uptake into skeletal muscle via the cation-independent mannose-6-phosphate (M6P) receptor (CIMPR) is limited. Avalglucosidase alfa has received marketing authorization in several countries for infantile-onset and/or late-onset Pompe disease. This recently approved enzyme replacement therapy (ERT) was glycoengineered to maximize CIMPR binding through high-affinity interactions with ∼7 bis-M6P moieties. Recently, small molecules like the glucosylceramide synthase inhibitor miglustat were reported to increase the stability of recombinant human acid α-glucosidase, and it was suggested that an increased serum half-life would result in better glycogen clearance. Here, the effects of miglustat on alglucosidase alfa and avalglucosidase alfa stability, activity, and efficacy in Pompe mice were evaluated. Although miglustat increased the stability of both enzymes in fluorescent protein thermal shift assays and when incubated in neutral pH buffer over time, it reduced their enzymatic activity by ∼50%. Improvement in tissue glycogen clearance and transcriptional dysregulation in Pompe mice correlated with M6P levels but not with miglustat coadministration. These results further substantiate the crucial role of CIMPR binding in lysosomal targeting of ERTs. SIGNIFICANCE STATEMENT: This work describes important new insights into the treatment of Pompe disease using currently approved enzyme replacement therapies (ERTs) coadministered with miglustat. Although miglustat increased the stability of ERTs in vitro, there was no positive impact to glycogen clearance and transcriptional correction in Pompe mice. However, increasing mannose-6-phosphate levels resulted in increased cell uptake in vitro and increased glycogen clearance and transcriptional correction in Pompe mice, further underscoring the crucial role of cation-independent mannose-6-phosphate receptor-mediated lysosomal targeting for ERTs.

Population Pharmacokinetic Modeling and Determination of Individual Exposure to Avalglucosidase Alfa in Adolescent and Adult Patients With Late-Onset Pompe Disease: Analysis of Pooled Data From Phase I to III Clinical Trials

BACKGROUND

Pompe disease is a rare genetic disorder caused by a deficiency of a lysosomal enzyme called acid alpha-glucosidase and is classified into infantile and late-onset forms. Since 2006, an enzyme replacement therapy involving alglucosidase alfa has been available. In 2021, a new enzyme replacement therapy involving avalglucosidase alfa demonstrated improved clinical benefits. In this article, the authors describe the pharmacokinetics of avalglucosidase alfa using a population pharmacokinetic approach.

METHODS

The population pharmacokinetic model was developed using a data set that included 75 patients and 2042 plasma drug concentrations determined through enzymatic activity assay from 3 studies (phases I/II and III) and involved 3 dose levels (5, 10, and 20 mg/kg). The analysis was performed using NONMEM software.

RESULTS

Two sequences were observed in the plasma drug concentration profile: the first kinetic driving exposure, and after 12 hours postdose, a slight rebound addressing very low concentrations that lasted up to 2 weeks. Following model screening, a model with a central compartment with parallel linear and nonlinear elimination and 2 concatenated peripheral compartments was proposed. A putative back-redistribution of a marginal fraction of the drug from the second peripheral compartment to the central compartment may explain the slight rebound in concentration. The final model's mean bias and precision for individual predictions were -2.66% and 30.7%, respectively, and -0.433% and 38.9%, respectively, for population predictions.

CONCLUSIONS

A concatenated 3-compartment model was developed to describe the avalglucosidase alfa concentrations in patients with late-onset Pompe disease. None of the covariates tested could explain the interindividual variability.

Glycogen storage diseases

Glycogen storage diseases (GSDs) are a group of rare, monogenic disorders that share a defect in the synthesis or breakdown of glycogen. This Primer describes the multi-organ clinical features of hepatic GSDs and muscle GSDs, in addition to their epidemiology, biochemistry and mechanisms of disease, diagnosis, management, quality of life and future research directions. Some GSDs have available guidelines for diagnosis and management. Diagnostic considerations include phenotypic characterization, biomarkers, imaging, genetic testing, enzyme activity analysis and histology. Management includes surveillance for development of characteristic disease sequelae, avoidance of fasting in several hepatic GSDs, medically prescribed diets, appropriate exercise regimens and emergency letters. Specific therapeutic interventions are available for some diseases, such as enzyme replacement therapy to correct enzyme deficiency in Pompe disease and SGLT2 inhibitors for neutropenia and neutrophil dysfunction in GSD Ib. Progress in diagnosis, management and definitive therapies affects the natural course and hence morbidity and mortality. The natural history of GSDs is still being described. The quality of life of patients with these conditions varies, and standard sets of patient-centred outcomes have not yet been developed. The landscape of novel therapeutics and GSD clinical trials is vast, and emerging research is discussed herein.

Hypertrophic Cardiomyopathy versus Storage Diseases with Myocardial Involvement

One of the main causes of heart failure is cardiomyopathies. Among them, the most common is hypertrophic cardiomyopathy (HCM), characterized by thickening of the left ventricular muscle. This article focuses on HCM and other cardiomyopathies with myocardial hypertrophy, including Fabry disease, Pompe disease, and Danon disease. The genetics and pathogenesis of these diseases are described, as well as current and experimental treatment options, such as pharmacological intervention and the potential of gene therapies. Although genetic approaches are promising and have the potential to become the best treatments for these diseases, further research is needed to evaluate their efficacy and safety. This article describes current knowledge and advances in the treatment of the aforementioned cardiomyopathies.

A Comprehensive Update on Late-Onset Pompe Disease

Pompe disease (PD) is an autosomal recessive disorder caused by mutations in the GAA gene that lead to a deficiency in the acid alpha-glucosidase enzyme. Two clinical presentations are usually considered, named infantile-onset Pompe disease (IOPD) and late-onset Pompe disease (LOPD), which differ in age of onset, organ involvement, and severity of disease. Assessment of acid alpha-glucosidase activity on a dried blood spot is the first-line screening test, which needs to be confirmed by genetic analysis in case of suspected deficiency. LOPD is a multi-system disease, thus requiring a multidisciplinary approach for efficacious management. Enzyme replacement therapy (ERT), which was introduced over 15 years ago, changes the natural progression of the disease. However, it has limitations, including a reduction in efficacy over time and heterogeneous therapeutic responses among patients. Novel therapeutic approaches, such as gene therapy, are currently under study. We provide a comprehensive review of diagnostic advances in LOPD and a critical discussion about the advantages and limitations of current and future treatments.

Hypersensitivity infusion-associated reactions induced by enzyme replacement therapy in a cohort of patients with late-onset Pompe disease: An experience from the French Pompe Registry

BACKGROUND AND OBJECTIVES

Pompe disease is a rare hereditary glycogen storage disorder due to lysosomal acid alpha-glucosidase deficiency. Enzyme replacement therapy (ERT) is the only available treatment. Infusion-associated reactions (IAR) are challenging since there are no guidelines for ERT rechallenge after a drug hypersensitivity reaction (DHR) in Pompe disease. The objective of the present study was to describe IAR and their management in late-onset Pompe disease (LOPD) patients in France, and to discuss the various possibilities of ERT rechallenge.

METHODS

An exhaustive screening of LOPD patients receiving ERT between 2006 and 2020 from the 31-participating hospital-based or reference centers was performed. The patients who had presented at least one hypersensitivity IAR (=DHR) episode were included. Demographic characteristics of the patients, IAR onset and timing, were retrospectively collected from the French Pompe Registry.

RESULTS

Fifteen patients among 115 treated LOPD patients in France presented at least 1 IAR; 80.0% were women. Twenty-nine IAR were reported; 18 (62.1%) IAR were Grade I reactions, 10 (34.5%) IAR were Grade II, and 1 (3.4%) IAR was Grade III. IgE-mediated hypersensitivity was found in 2/15 patients (13.3%). The median [IQR] time from ERT introduction to the first IAR was 15.0 months [11.0-24.0]. ERT was safely and effectively re-introduced either with premedication alone, or in combination with either modified regimen or desensitization protocol, in all 9 rechallenged patients; including in patients with IgE-mediated hypersensitivity, in the patient with the Grade III reaction, as well as in patients with very high anti-GAA titer.

DISCUSSION

Based on the results herein and previous reports, we discuss premedication and modified regimen for Grade I reactions, and desensitization in Grade II and III reactions. In conclusion, ERT-induced IAR can be safely and effectively managed with a modified regimen or desensitization protocol in LOPD patients.

Efficacy and Safety of Avalglucosidase Alfa in Patients With Late-Onset Pompe Disease After 97 Weeks: A Phase 3 Randomized Clinical Trial

Importance

In the previously reported Comparative Enzyme Replacement Trial With neoGAA Versus rhGAA (COMET) trial, avalglucosidase alfa treatment for 49 weeks showed clinically meaningful improvements in upright forced vital capacity (FVC) percent predicted and 6-minute walk test (6MWT) compared with alglucosidase alfa.

Objective

To report avalglucosidase alfa treatment outcomes during the COMET trial extension.

Design, Setting, and Participants

This phase 3 double-blind randomized clinical trial with crossover in the extension period enrolled patients 3 years and older with previously untreated late-onset Pompe disease (LOPD) between November 2, 2016, and February 10, 2021, with primary analysis after 49 weeks. Patients were treated at 55 referral centers in 20 countries. Efficacy outcomes were assessed at 97 weeks and safety outcomes to last follow-up, with data cutoff at February 10, 2021. Data were analyzed from May to June 2021.

Interventions

Random assignment (1:1) to receive 20 mg/kg of avalglucosidase alfa or alglucosidase alfa by intravenous infusion every other week for 49 weeks; thereafter, all patients received 20 mg/kg of avalglucosidase alfa every other week.

Main Outcomes and Measures

The primary outcome was the least squares (LS) mean change from baseline in FVC percent predicted. Secondary outcomes included the LS mean change from baseline in 6MWT, muscle strength, motor function, quality of life, and disease biomarkers. Safety and tolerability were also assessed.

Results

Of 100 participants from the double-blind treatment period, 95 entered the extension period. Of these, 51 (54%) were men, and the mean (range) age was 48.3 (10-79) years. At the start of this study, mean upright FVC percent predicted was similar between treatment arms, and 6MWT distance was greater in the avalglucosidase alfa arm. From baseline to week 97, LS mean (SE) FVC percent predicted increased by 2.65 (1.05) for those who continued avalglucosidase alfa and 0.36 (1.12) for those who switched to avalglucosidase alfa. The LS mean (SE) 6MWT distance increased by 18.60 (12.01) m and 4.56 (12.44) m, respectively. For participants who switched to avalglucosidase alfa, FVC percent predicted remained stable (LS mean [SE] change from week 49 to 97, 0.09 [0.88]) and 6MWT distance improved (LS mean [SE] change from week 49 to 97, 5.33 [10.81] m). Potentially treatment-related adverse events were reported in 29 patients (56.9%) who continued avalglucosidase alfa and in 25 patients (56.8%) who switched.

Conclusions and Relevance

In this randomized clinical trial extension, maintenance of positive clinical outcomes was demonstrated for patients continuing avalglucosidase alfa treatment and, to a lesser extent, patients who switched from alglucosidase alfa. No new safety concerns were observed.

Trial Registration

ClinicalTrials.gov Identifier: NCT02782741.

Hypersensitivity reaction during enzyme replacement therapy in lysosomal storage disorders. A systematic review of desensitization strategies

Lysosomal storage diseases (LSDs) are rare genetic metabolic disorders that cause the accumulation of glycosaminoglycans in lysosomes due to enzyme deficiency or reduced function. Enzyme replacement therapy (ERT) represents the gold standard treatment, but hypersensitivity reaction can occur resulting in treatment discontinuation. Thus, desensitization procedures for different culprit recombinant enzymes can be performed to restore ERT. We searched desensitization procedures performed in LSDs and focused on skin test results, protocols and premedication performed, and breakthrough reactions occurred during infusions. Fifty-two patients have been subjected to desensitization procedures successfully. Skin tests, with the culprit recombinant enzyme, deemed positive in 29 cases, doubtful in two cases, and not performed in four patients. Moreover, 29 of the 52 desensitization protocols used at the first infusion were breakthrough reaction free. Different desensitization strategies have proved safe and effective in restoring ERT in patients with previous hypersensitivity reactions. Most of these events seem to be Type I hypersensitivity reactions (IgE-mediated). Standardized in vivo and in vitro testing is necessary to better estimate the risk of the procedure and find the safest individualized desensitization protocol.

Transcriptomic characterization of clinical skeletal muscle biopsy from late-onset Pompe patients

Pompe disease is a rare lysosomal storage disorder arising from recessive mutations in the acid α-glucosidase gene and resulting in the accumulation of glycogen, particularly in the cardiac and skeletal muscle. The current standard of care is administration of enzyme replacement therapy in the form of alglucosidase alfa or the recently approved avalglucosidase alfa. In order to better understand the underlying cellular processes that are disrupted in Pompe disease, we conducted gene expression analysis on skeletal muscle biopsies obtained from late-onset Pompe disease patients (LOPD) prior to treatment and following six months of enzyme replacement with avalglucosidase alfa. The LOPD patients had a distinct transcriptomic signature as compared to control patient samples, largely characterized by perturbations in pathways involved in lysosomal function and energy metabolism. Although patients were highly heterogeneous, they collectively exhibited a strong trend towards attenuation of the dysregulated genes following just six months of treatment. Notably, the enzyme replacement therapy had a strong stabilizing effect on gene expression, with minimal worsening in genes that were initially dysregulated. Many of the cellular process that were altered in LOPD patients were also affected in the more clinically severe infantile-onset (IOPD) patients. Additionally, both LOPD and IOPD patients demonstrated enrichment across several inflammatory pathways, despite a lack of overt immune cell infiltration. This study provides further insight into Pompe disease biology and demonstrates the positive effects of avalglucosidase alfa treatment.

Safety and efficacy of avalglucosidase alfa in individuals with infantile-onset Pompe disease enrolled in the phase 2, open-label Mini-COMET study: The 6-month primary analysis report

PURPOSE

Mini-COMET (NCT03019406; Sanofi) is a phase 2, open-label, ascending-dose, 3-cohort study, evaluating avalglucosidase alfa safety, pharmacokinetics, and efficacy in individuals with infantile-onset Pompe disease aged <18 years who previously received alglucosidase alfa and showed clinical decline (cohorts 1 and 2) or suboptimal response (cohort 3).

METHODS

During a 25-week primary analysis period, cohorts 1 and 2 received avalglucosidase alfa 20 and 40 mg/kg every other week, respectively, for 6 months, whereas cohort 3 individuals were randomized (1:1) to receive avalglucosidase alfa 40 mg/kg every other week or alglucosidase alfa (current stable dose) for 6 months.

RESULTS

In total, 22 individuals were enrolled (cohort 1 [n = 6], cohort 2 [n = 5], cohort 3-avalglucosidase alfa [n = 5], and cohort 3-alglucosidase alfa [n = 6]). Median treatment compliance was 100%. None of the individuals discontinued treatment or died. Percentages of individuals with treatment-emergent adverse events were similar across dose and treatment groups. No serious or severe treatment-related treatment-emergent adverse events occurred. Trends for better motor function from baseline to week 25 were observed for 40 mg/kg every other week avalglucosidase alfa compared with either 20 mg/kg every other week avalglucosidase alfa or alglucosidase alfa up to 40 mg/kg weekly.

CONCLUSION

These data support the positive clinical effect of avalglucosidase alfa in patients with infantile-onset Pompe disease previously declining on alglucosidase alfa.

Motor Function Characteristics of Adults With Late-Onset Pompe Disease: A Systematic Scoping Review

BACKGROUND AND OBJECTIVES

Pompe disease is a rare neuromuscular disease caused by a deficiency of the lysosomal enzyme acid α-glucosidase. The late-onset Pompe disease (LOPD) in adults is characterized by weakness of ventilatory, axial, and proximal extremity muscles. These muscle impairments progressively impair various motor functions such as locomotion and postural control. Nearly 87% of adults with LOPD (aLOPD) report walking problems, and more than 80% report instability and falls. Knowledge of these motor functions is now sufficient to provide a clear and comprehensive overview of motor function in aLOPD. Therefore, this scoping review aimed to summarize current knowledge about motor function in aLOPD. It specifically targeted neuromuscular performance, locomotion, and postural control.

METHODS

A systematic search in MEDLINE (through PubMed), EMBASE, and Cochrane databases was conducted until May 2021. We included studies providing primary data on at least 4 participants, exploring neuromuscular performance, locomotion, and/or postural control in aLOPD. Risk of bias analysis was assessed using tools appropriate to the study designs; the risk of bias 2 (Cochrane tool) for randomized controlled trials, risk of bias in Nonrandomized Studies - of Interventions (Cochrane tool) for nonrandomized interventional trials, and the Newcastle-Ottawa Scale for cohort studies and case-control studies.

RESULTS

The search identified 2,885 articles. After screening, 58 articles were included in the analysis. In these studies, 88% explored locomotion, 83% neuromuscular performance, and 3% postural control. This review showed that aLOPD experience symmetrical weakness, concerning especially the hip and lumbar muscles. Locomotor activities are limited with a distance reduction, spatiotemporal gait parameter modification, and an increased pelvic drop and tilt. Balance disorders are also observed especially in the anteroposterior direction.

DISCUSSION

We performed the first review on motor function characteristics in aLOPD. Although a significant amount of knowledge was synthesized in this review, our study also highlighted the lack of current research on this topic. Maximal muscle strength was the only neuromuscular performance studied, and gait biomechanics and postural control were poorly explored in LOPD. Relationships between the degree of muscle weakness and motor function alterations also remain to be determined in aLOPD.

Therapeutic Options for the Management of Pompe Disease: Current Challenges and Clinical Evidence in Therapeutics and Clinical Risk Management

Pompe disease is a genetic disorder produced by mutations in the GAA gene leading to absence or reduced expression of acid alpha-glucosidase, an enzyme that metabolizes the breakdown of glycogen into glucose. There are two main phenotypes, the infantile consisting of early onset severe weakness and cardiomyopathy, and the adult which is characterized by slowly progressive skeletal and respiratory muscle weakness. Enzymatic replacement therapy (ERT) has been available for Pompe disease for more than 15 years. Although the treatment has improved many aspects of the disease, such as prolonged survival through improved cardiomyopathy and acquisition of motor milestones in infants and slower progression rate in adults, ERT is far from being a cure as both infantile and adult patients continue to progress. This fact has prompted the development of improved or new enzymes and other treatments such as gene therapy or substrate reduction strategies. Here, we review the data obtained from randomized clinical trials but also from open-label studies published so far that have assessed the advantages and limitations of this therapy. Moreover, we also review the new therapeutic strategies that are under development and provide our opinion on which are the unmet needs for patients with this disease.

Emerging Perspectives on Gene Therapy Delivery for Neurodegenerative and Neuromuscular Disorders

Neurodegenerative disorders (NDDs), such as Alzheimer's disease (AD) and Parkinson's Disease (PD), are a group of heterogeneous diseases that mainly affect central nervous system (CNS) functions. A subset of NDDs exhibit CNS dysfunction and muscle degeneration, as observed in Gangliosidosis 1 (GM1) and late stages of PD. Neuromuscular disorders (NMDs) are a group of diseases in which patients show primary progressive muscle weaknesses, including Duchenne Muscular Dystrophy (DMD), Pompe disease, and Spinal Muscular Atrophy (SMA). NDDs and NMDs typically have a genetic component, which affects the physiological functioning of critical cellular processes, leading to pathogenesis. Currently, there is no cure or efficient treatment for most of these diseases. More than 200 clinical trials have been completed or are currently underway in order to establish safety, tolerability, and efficacy of promising gene therapy approaches. Thus, gene therapy-based therapeutics, including viral or non-viral delivery, are very appealing for the treatment of NDDs and NMDs. In particular, adeno-associated viral vectors (AAV) are an attractive option for gene therapy for NDDs and NMDs. However, limitations have been identified after systemic delivery, including the suboptimal capacity of these therapies to traverse the blood-brain barrier (BBB), degradation of the particles during the delivery, high reactivity of the patient's immune system during the treatment, and the potential need for redosing. To circumvent these limitations, several preclinical and clinical studies have suggested intrathecal (IT) delivery to target the CNS and peripheral organs via cerebrospinal fluid (CSF). CSF administration can vastly improve the delivery of small molecules and drugs to the brain and spinal cord as compared to systemic delivery. Here, we review AAV biology and vector design elements, different therapeutic routes of administration, and highlight CSF delivery as an attractive route of administration. We discuss the different aspects of neuromuscular and neurodegenerative diseases, such as pathogenesis, the landscape of mutations, and the biological processes associated with the disease. We also describe the hallmarks of NDDs and NMDs as well as discuss current therapeutic approaches and clinical progress in viral and non-viral gene therapy and enzyme replacement strategies for those diseases.

Screening chimeric GAA variants in preclinical study results in hematopoietic stem cell gene therapy candidate vectors for Pompe disease

Pompe disease is a rare genetic neuromuscular disorder caused by acid α-glucosidase (GAA) deficiency resulting in lysosomal glycogen accumulation and progressive myopathy. Enzyme replacement therapy, the current standard of care, penetrates poorly into the skeletal muscles and the peripheral and central nervous system (CNS), risks recombinant enzyme immunogenicity, and requires high doses and frequent infusions. Lentiviral vector-mediated hematopoietic stem and progenitor cell (HSPC) gene therapy was investigated in a Pompe mouse model using a clinically relevant promoter driving nine engineered GAA coding sequences incorporating distinct peptide tags and codon optimizations. Vectors solely including glycosylation-independent lysosomal targeting tags enhanced secretion and improved reduction of glycogen, myofiber, and CNS vacuolation in key tissues, although GAA enzyme activity and protein was consistently lower compared with native GAA. Genetically modified microglial cells in brains were detected at low levels but provided robust phenotypic correction. Furthermore, an amino acid substitution introduced in the tag reduced insulin receptor-mediated signaling with no evidence of an effect on blood glucose levels in Pompe mice. This study demonstrated the therapeutic potential of lentiviral HSPC gene therapy exploiting optimized GAA tagged coding sequences to reverse Pompe disease pathology in a preclinical mouse model, providing promising vector candidates for further investigation.

Liposomal formulations for treating lysosomal storage disorders

Lysosomal storage disorders (LSD) are a group of rare life-threatening diseases caused by a lysosomal dysfunction, usually due to the lack of a single enzyme required for the metabolism of macromolecules, which leads to a lysosomal accumulation of specific substrates, resulting in severe disease manifestations and early death. There is currently no definitive cure for LSD, and despite the approval of certain therapies, their effectiveness is limited. Therefore, an appropriate nanocarrier could help improve the efficacy of some of these therapies. Liposomes show excellent properties as drug carriers, because they can entrap active therapeutic compounds offering protection, biocompatibility, and selectivity. Here, we discuss the potential of liposomes for LSD treatment and conduct a detailed analysis of promising liposomal formulations still in the preclinical development stage from various perspectives, including treatment strategy, manufacturing, characterization, and future directions for implementing liposomal formulations for LSD.

Therapeutic thoroughfares for adults living with Pompe disease

PURPOSE OF REVIEW

Pompe disease is caused by autosomal recessive mutations in the acid α-glucosidase gene leading to a multiorgan deficiency of the enzyme acid glucosidase alfa. To recover to a nondiseased status, a lift over a threshold of 25% acid glucosidase alfa enzyme activity is required. This update on therapeutic thoroughfares for adult Pompe disease aims to assist neuromuscular and metabolic specialists.

RECENT FINDINGS

We reviewed the recent studies covering enzyme replacement therapy, gene therapy, and substrate reduction therapy in adult Pompe disease. Results of phase 3 studies and the first sets of long-term data of both novel enzyme replacement therapies, avalglucosidase alfa, and ciplaglucodsidase alfa combined with miglustat, are public. First gene therapy trials are ongoing. Substrate reduction therapy is in early transition to the clinical trial phase. We still miss dose escalation and intensification of frequency trials on enzyme replacement therapy in adults, probably suitable to echo current results in infantile and juvenile Pompe disease.

SUMMARY

Therapy of Pompe disease reaches new thoroughfares reducing the overall disease burden of patients; however, individualization of these novel therapeutic options remains challenging. Consensus-based and shared decision-based recommendations need to be established based on reliable real-world data to allow the best standards of care worldwide.

The Clinical Management of Pompe Disease: A Pediatric Perspective

Pompe disease (PD) is an inherited metabolic disorder caused by a deficiency of acid α-glucosidase (GAA), leading to lysosomal accumulation of glycogen, mainly in skeletal and cardiac muscles as well as the nervous system. Patients with PD develop cellular dysfunction and muscle damage. PD can be classified into two classic forms, namely infantile-onset PD (IOPD) and late-onset PD (LOPD). Delayed treatment, particularly in IOPD, would result in significant organ damage and early death. Nonetheless, early diagnosis and timely treatment are often hampered by the rarity of PD and its wide variety of, but overlapping, symptoms. This article reviews the common clinical presentations of PD and outlines the essentials of PD management. In particular, the implications of newborn screening (NBS) and clinical performance of enzyme replacement therapy (ERT) are highlighted.

Long-term Safety and Efficacy of Avalglucosidase Alfa in Patients With Late-Onset Pompe Disease

BACKGROUND AND OBJECTIVES

Pompe disease is a rare, progressive neuromuscular disorder caused by deficiency of lysosomal acid α-glucosidase (GAA) and subsequent glycogen accumulation. Avalglucosidase alfa, a recombinant human GAA enzyme replacement therapy designed for increased cellular uptake and glycogen clearance, has been studied for long-term efficacy and safety in patients with late-onset Pompe disease (LOPD). Here, we report up to 6.5 years' experience with avalglucosidase alfa during the NEO1 and NEO-EXT studies.

METHODS

NEO1 participants with LOPD, either treatment naive (Naive Group) or receiving alglucosidase alfa for ≥9 months (Switch Group), received avalglucosidase alfa (5, 10, or 20 mg/kg every other week [qow]) for 6 months before entering NEO-EXT and continued their NEO1 dose until all proceeded with 20 mg/kg qow. Safety and efficacy, a prespecified exploratory secondary outcome, were assessed; slopes of change for efficacy outcomes were calculated from a repeated mixed-measures model.

RESULTS

Twenty-four participants enrolled in NEO1 (Naive Group, n = 10; Switch Group, n = 14); 21 completed and 19 entered NEO-EXT; in February 2020, 17 participants remained in NEO-EXT, with data up to 6.5 years. Avalglucosidase alfa was generally well tolerated during NEO-EXT, with a safety profile consistent with that in NEO1. No deaths or treatment-related life-threatening serious adverse events occurred. Eighteen participants developed antidrug antibodies without apparent effect on clinical outcomes. No participants who were tested developed immunoglobulin E antibodies. Upright forced vital capacity %predicted remained stable in most participants, with slope estimates (95% CIs) of -0.473 per year (-1.188 to 0.242) and -0.648 per year (-1.061 to -0.236) in the Naive and Switch Groups, respectively. Six-minute walk test (6MWT) %predicted was also stable for most participants, with slope estimates of -0.701 per year (-1.571 to 0.169) and -0.846 per year (-1.567 to -0.125) for the Naive and Switch Groups, respectively. Improvements in 6MWT distance were observed in most participants aged <45 years at NEO1 enrollment in both the Naive and Switch Groups.

DISCUSSION

Avalglucosidase alfa was generally well tolerated for up to 6.5 years in adult participants with LOPD either naive to alglucosidase alfa or who had previously received alglucosidase alfa for ≥9 months.

CLASSIFICATION OF EVIDENCE

This study provides Class IV evidence of long-term tolerability and sustained efficacy of avalglucosidase alfa in patients with LOPD after up to 6.5 years.

TRIAL REGISTRATION INFORMATION

NCT01898364 (NEO1 first posted: July 12, 2013; clinicaltrials.gov/ct2/show/NCT01898364); NCT02032524 (NEO-EXT first posted: January 10, 2014; clinicaltrials.gov/ct2/show/NCT02032524). First participant enrollment: NEO1-August 19, 2013; NEO-EXT-February 27, 2014.

MRI changes in diaphragmatic motion and curvature in Pompe disease over time

OBJECTIVES

To evaluate changes in diaphragmatic function in Pompe disease using MRI over time, both during natural disease course and during treatment with enzyme replacement therapy (ERT).

METHODS

In this prospective study, 30 adult Pompe patients and 10 healthy controls underwent pulmonary function tests and spirometry-controlled MRI twice, with an interval of 1 year. In the sagittal view of 3D gradient echo breath-hold acquisitions, diaphragmatic motion (cranial-caudal ratio between end-inspiration and end-expiration) and curvature (diaphragm height and area ratio) were calculated using a machine learning algorithm based on convolutional neural networks. Changes in outcomes after 1 year were compared between Pompe patients and healthy controls using the Mann-Whitney test.

RESULTS

Pulmonary function outcomes and cranial-caudal ratio in Pompe patients did not change significantly over time compared to healthy controls. Diaphragm height ratio increased by 0.04 (-0.38 to 1.79) in Pompe patients compared to -0.02 (-0.18 to 0.25) in healthy controls (p = 0.02). An increased diaphragmatic curvature over time was observed in particular in untreated Pompe patients (p = 0.03), in those receiving ERT already for over 3 years (p = 0.03), and when severe diaphragmatic weakness was found on the initial MRI (p = 0.01); no progression was observed in Pompe patients who started ERT less than 3 years ago and in Pompe patients with mild diaphragmatic weakness on their initial MRI.

CONCLUSIONS

MRI enables to detect small changes in diaphragmatic curvature over 1-year time in Pompe patients. It also showed that once severe diaphragmatic weakness has occurred, improvement of diaphragmatic muscle function seems unlikely.

KEY POINTS

• Changes in diaphragmatic curvature in Pompe patients over time assessed with 3D MRI may serve as an outcome measure to evaluate the effect of treatment on diaphragmatic function. • Diaphragmatic curvature showed a significant deterioration after 1 year in Pompe patients compared to healthy controls, but the curvature seems to remain stable over this period in patients who were treated with enzyme replacement therapy for less than 3 years, possibly indicating a positive effect of ERT. • Improvement of diaphragmatic curvature over time is rarely seen in Pompe patients once diaphragmatic motion shows severe impairment (cranial-caudal inspiratory/expiratory ratio < 1.4).

Modern therapeutic approaches to liver-related disorders

The liver is a key production and processing site that is essential for health. Liver dysfunction can result in both systemic and liver-specific diseases. To combat these diseases, genetic approaches have been developed that have high liver tropism and are based on gene addition/editing or gene silencing. The gene addition/editing approach has yielded encouraging clinical data on the use of viral vectors in patients with haemophilia, as well as neuromuscular diseases, and has led to trials for liver-related disorders. However, the immune response and the long-term stability of exogenous expression remain important challenges. Gene editing and mRNA therapy have yielded first in-human proof-of-concept therapeutics and vaccines, but the road to the treatment of liver-related disorders remains long. Gene silencing is accomplished primarily via antisense oligonucleotides and small-interfering RNAs (siRNAs). siRNA modification with N-acetyl galactosamine results in hepatocellular-specific targeting and catapulted the liver to the centre of siRNA research. Several siRNA drugs for liver-related disorders have recently been approved, and the pipeline of drugs under investigation is crowded. Loss-of-function mutations might also be treated with enzyme substitution therapy. This review summarises current genetic approaches as well as key enzyme substitution therapies, focusing on recently approved compounds, potential adverse effects, and future challenges. Collectively, these recent advances place the liver at the forefront of precision medicine for metabolic and genetic diseases and are expected to transform the care and treatment of patients with both liver-specific and systemic diseases.

Therapeutic Approaches in Lysosomal Storage Diseases

Lysosomal Storage Diseases are multisystemic disorders determined by genetic variants, which affect the proteins involved in lysosomal function and cellular metabolism. Different therapeutic approaches, which are based on the physiologic mechanisms that regulate lysosomal function, have been proposed for these diseases. Currently, enzyme replacement therapy, gene therapy, or small molecules have been approved or are under clinical development to treat lysosomal storage disorders. The present article reviews the main therapeutic strategies that have been proposed so far, highlighting possible limitations and future perspectives.

Safety and efficacy of avalglucosidase alfa versus alglucosidase alfa in patients with late-onset Pompe disease (COMET): a phase 3, randomised, multicentre trial

BACKGROUND

Pompe disease is a rare, progressive neuromuscular disorder caused by deficiency of acid α-glucosidase (GAA) and accumulation of lysosomal glycogen. We assessed the safety and efficacy of avalglucosidase alfa, a recombinant human GAA enzyme replacement therapy specifically designed for enhanced mannose-6-phosphate-receptor targeting and enzyme uptake aimed at increased glycogen clearance, compared with the current approved standard of care, alglucosidase alfa, in patients with late-onset Pompe disease.

METHODS

We did a randomised, double-blind, phase 3 trial at 55 sites in 20 countries. We enrolled individuals (aged ≥3 years) with enzymatically confirmed late-onset Pompe disease who had never received treatment. We used a centralised treatment allocation system to randomly allocate participants to either avalglucosidase alfa or alglucosidase alfa. Participants and investigators were unaware of their treatment allocation. The primary outcome measure was change from baseline to week 49 in upright forced vital capacity percent (FVC%) predicted. We used a hierarchical fixed sequential testing strategy, whereby non-inferiority of avalglucosidase alfa compared with alglucosidase alfa was assessed first, with a non-inferiority margin of 1·1. If non-inferiority was seen, then superiority was tested with a 5% significance level. The key secondary objective was effect on functional endurance, measured by the 6-minute walk test (6MWT). Safety was assessed, including treatment-emergent adverse events and infusion-associated reactions. The modified intent-to-treat population was the primary analysis population for all efficacy analyses. The safety population was the analysis population for safety analyses. This trial is registered with ClinicalTrials.gov, NCT02782741. We report results of the 49-week primary analysis period.

FINDINGS

Between Nov 2, 2016, and March 29, 2019, 100 participants were randomly allocated avalglucosidase alfa (n=51) or alglucosidase alfa (n=49). Treatment with avalglucosidase alfa resulted in a least-squares mean improvement in upright FVC% predicted of 2·89% (SE 0·88) compared with 0·46% (0·93) with alglucosidase alfa at week 49 (difference 2·43% [95% CI -0·13 to 4·99]). Non-inferiority was shown because the lower bound of the 95% CI for the difference far exceeded the predefined non-inferiority margin but did not exclude 0 (p=0·0074). Superiority was not reached (p=0·063), so formal testing was stopped, as per the testing hierarchy. Improvements were also seen in the 6MWT with avalglucosidase alfa compared with alglucosidase alfa, with greater increases in distance covered (difference 30·01 m [95% CI 1·33 to 58·69]) and percent predicted (4·71% [0·25 to 9·17]). Treatment-emergent adverse events potentially related to treatment were reported in 23 (45%) of 51 participants in the avalglucosidase alfa group and in 24 (49%) of 49 in the alglucosidase alfa group, and infusion-associated reactions were reported in 13 (26%) participants in the avalglucosidase alfa group and 16 (33%) in the alglucosidase alfa group. Of the five trial withdrawals, all in the alglucosidase alfa group, four were due to adverse events, including two infusion-associated reactions. Serious treatment-emergent adverse events were reported in eight (16%) participants who received avalglucosidase alfa and in 12 (25%) who received alglucosidase alfa. One participant treated with alglucosidase alfa died because of acute myocardial infarction determined to be unrelated to treatment. Antidrug antibody responses were similar in both groups. High and persistent titres (≥12 800) and neutralising antibodies were more common with alglucosidase alfa (in 16 [33%] participants) than with avalglucosidase alfa (ten [20%]).

INTERPRETATION

We consider that this study provides evidence of clinically meaningful improvement with avalglucosidase alfa therapy over alglucosidase alfa in respiratory function, ambulation, and functional endurance, with no new safety signals reported. An open-label extended-treatment period is ongoing to confirm the long-term safety and efficacy of avalglucosidase alfa, with the aim for this therapy to become the new standard treatment in late-onset Pompe disease.

FUNDING

Sanofi Genzyme.

Hepatic expression of GAA results in enhanced enzyme bioavailability in mice and non-human primates

Pompe disease (PD) is a severe neuromuscular disorder caused by deficiency of the lysosomal enzyme acid alpha-glucosidase (GAA). PD is currently treated with enzyme replacement therapy (ERT) with intravenous infusions of recombinant human GAA (rhGAA). Although the introduction of ERT represents a breakthrough in the management of PD, the approach suffers from several shortcomings. Here, we developed a mouse model of PD to compare the efficacy of hepatic gene transfer with adeno-associated virus (AAV) vectors expressing secretable GAA with long-term ERT. Liver expression of GAA results in enhanced pharmacokinetics and uptake of the enzyme in peripheral tissues compared to ERT. Combination of gene transfer with pharmacological chaperones boosts GAA bioavailability, resulting in improved rescue of the PD phenotype. Scale-up of hepatic gene transfer to non-human primates also successfully results in enzyme secretion in blood and uptake in key target tissues, supporting the ongoing clinical translation of the approach.

Avalglucosidase alfa: First Approval

Avalglucosidase alfa (NEXVIAZYME™; avalglucosidase alfa-ngpt) is a hydrolytic lysosomal glycogen-specific recombinant human α-glucosidase product being developed by Sanofi Genzyme (formerly Genzyme Corporation) for the treatment of Pompe disease. Pompe disease is an autosomal recessive lysosomal storage disease caused by a deficiency of the lysosomal enzyme acid α-glucosidase (GAA), which results in intralysosomal accumulation of glycogen in various tissues. In August 2021, avalglucosidase alfa received its first approval in the USA for the treatment of patients 1 year of age and older with late-onset Pompe disease (GAA deficiency). In July 2021, avalglucosidase alfa received a positive opinion in the EU for long-term enzyme replacement therapy for the treatment of patients with Pompe disease. The drug is under regulatory review in the UK and Japan, and clinical studies are underway in several countries worldwide. This article summarizes the milestones in the development of avalglucosidase alfa leading to this first approval for late-onset Pompe disease.

Enzyme Replacement Therapy for Genetic Disorders Associated with Enzyme Deficiency

Mutations in human genes might lead to loss of functional proteins, causing diseases. Among these genetic disorders, a large class is associated with the deficiency in metabolic enzymes, resulting in both an increase in the concentration of substrates and a loss in the metabolites produced by the catalyzed reactions. The identification of therapeutic actions based on small molecules represents a challenge to medicinal chemists because the target is missing. Alternative approaches are biology-based, ranging from gene and stem cell therapy, CRISPR/Cas9 technology, distinct types of RNAs, and enzyme replacement therapy (ERT). This review will focus on the latter approach that since the 1990s has been successfully applied to cure many rare diseases, most of them being lysosomal storage diseases or metabolic diseases. So far, a dozen enzymes have been approved by FDA/EMA for lysosome storage disorders and only a few for metabolic diseases. Enzymes for replacement therapy are mainly produced in mammalian cells and some in plant cells and yeasts and are further processed to obtain active, highly bioavailable, less degradable products. Issues still under investigation for the increase in ERT efficacy are the optimization of enzymes interaction with cell membrane and internalization, the reduction in immunogenicity, and the overcoming of blood-brain barrier limitations when neuronal cells need to be targeted. Overall, ERT has demonstrated its efficacy and safety in the treatment of many genetic rare diseases, both saving newborn lives and improving patients' life quality, and represents a very successful example of targeted biologics.

The increasing role of muscle MRI to monitor changes over time in untreated and treated muscle diseases

PURPOSE OF REVIEW

This review aims to discuss the recent results of studies published applying quantitative MRI sequences to large cohorts of patients with neuromuscular diseases.

RECENT FINDINGS

Quantitative MRI sequences are now available to identify and quantify changes in muscle water and fat content. These two components have been associated with acute and chronic injuries, respectively. Studies show that the increase in muscle water is not only reversible if therapies are applied successfully but can also predict fat replacement in neurodegenerative diseases. Muscle fat fraction correlates with muscle function tests and increases gradually over time in parallel with the functional decline of patients with neuromuscular diseases. There are new spectrometry-based sequences to quantify other components, such as glycogen, electrolytes or the pH of the muscle fibre, extending the applicability of MRI to the study of several processes in neuromuscular diseases.

SUMMARY

The latest results obtained from the study of long cohorts of patients with various neuromuscular diseases open the door to the use of this technology in clinical trials, which would make it possible to obtain a new measure for assessing the effectiveness of new treatments. The challenge is currently the popularization of these studies and their application to the monitoring of patients in the daily clinic.

Adapting protein sequences for optimized therapeutic efficacy

Therapeutic proteins alleviate disease pathology by supplementing missing or defective native proteins, sequestering superfluous proteins, or by acting through designed non-natural mechanisms. Although therapeutic proteins often have the same amino acid sequence as their native counterpart, their maturation paths from expression to the site of physiological activity are inherently different, and optimizing protein sequences for properties that 100s of millions of years of evolution did not need to address presents an opportunity to develop better biological treatments. Because therapeutic proteins are inherently non-natural entities, optimization for their desired function should be considered analogous to that of small molecule drug candidates, which are optimized through expansive combinatorial variation by the medicinal chemist. Here, we review recent successes and challenges of protein engineering for optimized therapeutic efficacy.

STIG study: real-world data of long-term outcomes of adults with Pompe disease under enzyme replacement therapy with alglucosidase alfa

Background

Pompe disease is one of the few neuromuscular diseases with an approved drug therapy, which has been available since 2006. Our study aimed to determine the real-world long-term efficacy and safety of alglucosidase alfa.

Methods

This multicenter retrospective study (NCT02824068) collected data from adult Pompe disease patients receiving ERT for at least 3 years. Demographics and baseline characteristics, muscle strength, lung function (FVC), walking capability (6MWT), and safety were assessed once a year. Evaluation was done on the group and individual levels, using quantitative linear models (t test) and general univariate linear models (ANOVA).

Findings

Sixty-eight adult Pompe disease patients from four countries (Spain, Taiwan, Italy, Germany (STIG)) participated. The mean follow-up was 7.03 years ± 2.98. At group level in all outcome measures, an initial improvement followed by a secondary decline was observed. After 10 years, the 6MWT_%pred showed the most sustained positive effect (p = 0.304). The MRC_%max remained stable with a mild decline (p = 0.131), however, FVC_%pred deteriorated significantly (p < 0.001) by 14.93% over 10 years of ERT. The progression rate of FVC_%pred under ERT could be explained in most of the patients (83.5%) by the disease severity at baseline. Furthermore, our study shows a decline in the FVC combined with an increase in non-invasive and invasive ventilation requirements in adult Pompe disease patients over time.

Conclusions

The STIG real-world study confirms an initial efficacy of ERT in the first years with a secondary sustained decline in multiple outcome measures. Further efforts are required to establish a more valid long-term monitoring and improved therapies.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00415-021-10409-9.

The rapidly evolving view of lysosomal storage diseases

Lysosomal storage diseases are a group of metabolic disorders caused by deficiencies of several components of lysosomal function. Most commonly affected are lysosomal hydrolases, which are involved in the breakdown and recycling of a variety of complex molecules and cellular structures. The understanding of lysosomal biology has progressively improved over time. Lysosomes are no longer viewed as organelles exclusively involved in catabolic pathways, but rather as highly dynamic elements of the autophagic-lysosomal pathway, involved in multiple cellular functions, including signaling, and able to adapt to environmental stimuli. This refined vision of lysosomes has substantially impacted on our understanding of the pathophysiology of lysosomal disorders. It is now clear that substrate accumulation triggers complex pathogenetic cascades that are responsible for disease pathology, such as aberrant vesicle trafficking, impairment of autophagy, dysregulation of signaling pathways, abnormalities of calcium homeostasis, and mitochondrial dysfunction. Novel technologies, in most cases based on high-throughput approaches, have significantly contributed to the characterization of lysosomal biology or lysosomal dysfunction and have the potential to facilitate diagnostic processes, and to enable the identification of new therapeutic targets.