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.

Complex Transposon Insertion as a Novel Cause of Pompe Disease.

Pompe disease (OMIM#232300) is an autosomal recessive lysosomal storage disorder caused by mutations in the GAA gene. According to public mutation databases, more than 679 pathogenic variants have been described in GAA, none of which are associated with mobile genetic elements. In this article, we report a novel molecular genetic cause of Pompe disease, which could be hardly detected using routine molecular genetic analysis. Whole genome sequencing followed by comprehensive functional analysis allowed us to discover and characterize a complex mobile genetic element insertion deep in the intron 15 of the GAA gene in a patient with infantile onset Pompe disease.

Pompe disease: pathogenesis, molecular genetics and diagnosis.

Pompe disease (PD) is a rare autosomal recessive disorder caused by mutations in the GAA gene, localized on chromosome 17 and encoding for acid alpha-1,4-glucosidase (GAA). Currently, more than 560 mutations spread throughout GAA gene have been reported. GAA catalyzes the hydrolysis of α-1,4 and α-1,6-glucosidic bonds of glycogen and its deficiency leads to lysosomal storage of glycogen in several tissues, particularly in muscle. PD is a chronic and progressive pathology usually characterized by limb-girdle muscle weakness and respiratory failure. PD is classified as infantile and childhood/adult forms. PD patients exhibit a multisystemic manifestation that depends on age of onset.Early diagnosis is essential to prevent or reduce the irreversible organ damage associated with PD progression. Here, we make an overview of PD focusing on pathogenesis, clinical phenotypes, molecular genetics, diagnosis, therapies, autophagy and the role of miRNAs as potential biomarkers for PD.

Moss-Derived Human Recombinant GAA Provides an Optimized Enzyme Uptake in Differentiated Human Muscle Cells of Pompe Disease.

Pompe disease is an autosomal recessive lysosomal storage disorder (LSD) caused by deficiency of lysosomal acid alpha-glucosidase (GAA). The result of the GAA deficiency is a ubiquitous lysosomal and non-lysosomal accumulation of glycogen. The most affected tissues are heart, skeletal muscle, liver, and the nervous system. Replacement therapy with the currently approved enzyme relies on M6P-mediated endocytosis. However, therapeutic outcomes still leave room for improvement, especially with regard to skeletal muscles. We tested the uptake, activity, and effect on glucose metabolism of a non-phosphorylated recombinant human GAA produced in moss (moss-GAA). Three variants of moss-GAA differing in glycosylation pattern have been analyzed: two with terminal mannose residues in a paucimannosidic (Man3) or high-mannose (Man 5) configuration and one with terminal N-acetylglucosamine residues (GnGn). Compared to alglucosidase alfa the moss-GAA GnGn variant showed increased uptake in differentiated myotubes. Moreover, incubation of immortalized muscle cells of Gaa-/- mice with moss-GAA GnGn led to similarly efficient clearance of accumulated glycogen as with alglucosidase alfa. These initial data suggest that M6P-residues might not always be necessary for the cellular uptake in enzyme replacement therapy (ERT) and indicate the potential of moss-GAA GnGn as novel alternative drug for targeting skeletal muscle in Pompe patients.

Links between autophagy and disorders of glycogen metabolism - Perspectives on pathogenesis and possible treatments.

The glycogen storage diseases are a group of inherited metabolic disorders that are characterized by specific enzymatic defects involving the synthesis or degradation of glycogen. Each disorder presents with a set of symptoms that are due to the underlying enzyme deficiency and the particular tissues that are affected. Autophagy is a process by which cells degrade and recycle unneeded or damaged intracellular components such as lipids, glycogen, and damaged mitochondria. Recent studies showed that several of the glycogen storage disorders have abnormal autophagy which can disturb normal cellular metabolism and/or mitochondrial function. Here, we provide a clinical overview of the glycogen storage disorders, a brief description of autophagy, and the known links between specific glycogen storage disorders and autophagy.

A computational method to characterize the missense mutations in the catalytic domain of GAA protein causing Pompe disease.

Pompe disease is an autosomal recessive lysosomal storage disease caused by acid α-glucosidase (GAA) deficiency, resulting in intralysosomal accumulation of glycogen, including cardiac, skeletal, and smooth muscle cells. The GAA gene is located on chromosome 17 (17q25.3), the GAA protein consists of 952 amino acids; of which 378 amino acids (347-726) falls within the catalytic domain of the protein and comprises of active sites (518 and 521) and binding sites (404, 600, 616, and 674). In this study, we used several computational tools to classify the missense mutations in the catalytic domain of GAA for their pathogenicity and stability. Eight missense mutations (R437C, G478R, N573H, Y575S, G605D, V642D, L705P, and L712P) were predicted to be pathogenic and destabilizing to the protein structure. These mutations were further subjected to phenotyping analysis using SNPeffect 4.0 to predict the chaperone binding sites and structural stability of the protein. The mutations R437C and G478R were found to compromise the chaperone-binding activity with GAA. Molecular docking analysis revealed that the G478R mutation to be more significant and hinders binding to the DNJ (Miglustat) compared with the R437C. Further molecular dynamic analysis for the two mutations demonstrated that the G478R mutation was acquired higher deviation, fluctuation, and lower compactness with decreased intramolecular hydrogen bonds compared to the mutant R437C. These data are expected to serve as a platform for drug design against Pompe disease and will serve as an ultimate tool for variant classification and interpretations.

Satellite cells fail to contribute to muscle repair but are functional in Pompe disease (glycogenosis type II).

Pompe disease, which is due to acid alpha-glucosidase deficiency, is characterized by skeletal muscle dysfunction attributed to the accumulation of glycogen-filled lysosomes and autophagic buildup. Despite the extensive tissue damages, a failure of satellite cell (SC) activation and lack of muscle regeneration have been reported in patients. However, the origin of this defective program is unknown. Additionally, whether these deficits occur gradually over the disease course is unclear. Using a longitudinal pathophysiological study of two muscles in a Pompe mouse model, here, we report that the enzymatic defect results in a premature saturating glycogen overload and a high number of enlarged lysosomes. The muscles gradually display profound remodeling as the number of autophagic vesicles, centronucleated fibers, and split fibers increases and larger fibers are lost. Only a few regenerated fibers were observed regardless of age, although the SC pool was preserved. Except for the early age, during which higher numbers of activated SCs and myoblasts were observed, no myogenic commitment was observed in response to the damage. Following in vivo injury, we established that muscle retains regenerative potential, demonstrating that the failure of SC participation in repair is related to an activation signal defect. Altogether, our findings provide new insight into the pathophysiology of Pompe disease and highlight that the activation signal defect of SCs compromises muscle repair, which could be related to the abnormal energetic supply following autophagic flux impairment.

Quantitative muscle MRI to follow up late onset Pompe patients: a prospective study.

Late onset Pompe disease (LOPD) is a slow, progressive disorder characterized by skeletal and respiratory muscle weakness. Enzyme replacement therapy (ERT) slows down the progression of muscle symptoms. Reliable biomarkers are needed to follow up ERT-treated and asymptomatic LOPD patients in clinical practice. In this study, 32 LOPD patients (22 symptomatic and 10 asymptomatic) underwent muscle MRI using 3-point Dixon and were evaluated at the time of the MRI with several motor function tests and patient-reported outcome measures, and again after one year. Muscle MRI showed a significant increase of 1.7% in the fat content of the thigh muscles in symptomatic LOPD patients. In contrast, there were no noteworthy differences between muscle function tests in the same period of time. We did not observe any significant changes either in muscle MRI or in muscle function tests in asymptomatic patients over the year. We conclude that 3-point Dixon muscle MRI is a useful tool for detecting changes in muscle structure in symptomatic LOPD patients and could become part of the current follow-up protocol in daily clinics.

Quantification of intramuscular fat in patients with late-onset Pompe disease by conventional magnetic resonance imaging for the long-term follow-up of enzyme replacement therapy.

OBJECTIVE: The objective of this study was to evaluate a quantitative method based on conventional T1-weighted magnetic resonance (MR) imaging to assess fatty muscular degeneration in patients with late-onset Pompe disease and to compare it with semi-quantitative visual evaluation (the Mercuri score). In addition, a long-term retrospective data analysis was performed to evaluate treatment response to enzyme replacement therapy with alglucosidase alfa. METHODS: MR images of the lumbar spine were acquired in 41 patients diagnosed with late-onset Pompe disease from 2006 through 2015. Two independent readers retrospectively evaluated fatty degeneration of the psoas and paraspinal muscles by applying the Mercuri score. Quantitative semi-automated muscle and fat tissue separation was performed, and inter-observer agreement and correlations with clinical parameters were assessed. Follow-up examinations were performed in 13 patients treated with alglucosidase alfa after a median of 39 months; in 7/13 patients, an additional follow-up examination was completed after a median of 63 months. RESULTS: Inter-observer agreement was high. Measurements derived from the quantitative method correlated well with Medical Research Council scores of muscle strength, with moderate correlations found for the 6-minute walk test, the 4-step stair climb test, and spirometry in the supine position. A significant increase in the MR-derived fat fraction of the psoas muscle was found between baseline and follow-up 1 (P = 0.016), as was a significant decrease in the performance on the 6-minute walk test (P = 0.006) and 4-step stair climb test (P = 0.034), as well as plasma creatine kinase (P = 0.016). No statistically significant difference in clinical or MR-derived parameters was found between follow-up 1 and follow-up 2. CONCLUSIONS: Quantification of fatty muscle degeneration using the semi-automated method can provide a more detailed overview of disease progression than semi-quantitative Mercuri scoring. MR-derived data correlated with clinical symptoms and patient exercise capacity. After an initial worsening, the fat fraction of the psoas muscle and performance on the 6-minute walk test stayed constant during long-term follow-up under enzyme replacement therapy.

Late-onset Pompe's disease in a hemodialysis patient: A first case report.

A 37-year-old hemodialysis patient appeared with unusual somnolence during 2 successive hemodialysis sessions. Blood gas analysis revealed hypercapnic respiratory failure and spirometry restrictive lung disease. After exclusion of other causes of restrictive lung disease with chest CT-scan and cerebrum MRI, electrophysiological study revealed myopathy. Because besides lordosis and limb-girdle gait the patient was ambulant the possibility of late-onset Pompe's disease was set and confirmed with evaluation of α-glucosidase activity and genetic analysis. Enzyme replacement therapy (ERT) with aglucosidase alfa was started. Due to inaccessibility of veins in the arm without the arteriovenous fistula, during the last 1 year, the patient received the ERT through the venous line of the hemodialysis circuit. Three years later the patient remains ambulant without the need of any assistant device and preserved his pulmonary function. This is the first described case of late-onset Pompe's disease in a hemodialysis patient treated with ERT.

Prevalence of late-onset pompe disease in Portuguese patients with diaphragmatic paralysis - DIPPER study.

Pompe disease is a rare autosomal recessive neuromuscular disorder caused by acid α-glucosidase enzyme (GAA) deficiency and divided into two distinct variants, infantile- and late-onset. The late-onset variant is characterized by a spectrum of phenotypic variation that may range from asymptomatic, to reduced muscle strength and/or diaphragmatic paralysis. Since muscle strength loss is characteristic of several different conditions, which may also cause diaphragmatic paralysis, a protocol was created to search for the diagnosis of Pompe disease and exclude other possible causes. METHODS: We collected a sample size of 18 patients (10 females, 8 males) with a median age of 60 years and diagnosis of diaphragmatic paralysis of unknown etiology, followed in the Pulmonology outpatient consultation of 9 centers in Portugal, over a 24-month study period. We evaluated data from patient's clinical and demographic characteristics as well as complementary diagnostic tests including blood tests, imaging, neurophysiologic and respiratory function evaluation. All patients were evaluated for GAA activity with DBS (dried blood test) or serum quantification and positive results confirmed by serum quantification and sequencing. RESULTS: Three patients were diagnosed with Pompe's disease and recommended for enzyme replacement therapy. The prevalence of Pompe, a rare disease, in our diaphragmatic paralysis patient sample was 16.8%. CONCLUSION: We conclude that DBS test for GAA activity should be recommended for all patients with diaphragmatic paralysis which, despite looking at all the most common causes, remains of unknown etiology; this would improve both the timing and accuracy of diagnosis for Pompe disease in this patient population. Accurate diagnosis will lead to improved care for this rare, progressively debilitating but treatable neuromuscular disease.

Stroke in Young-Dilative Arteriopathy: A Clue to Late-Onset Pompe's Disease?

IMPORTANCE: In almost a third of stroke in young cases, etiology remains unclear. We report a radiological entity which might give a clue toward detection of late onset Pompe's disease in some cases. OBSERVATION: Here we report two cases of stroke in young in which evaluation led to diagnosis of late onset Pompe's disease. Both patients presented with recurrent stroke. On evaluation, one of them was found to have slowly progressive predominantly proximal quadriparesis. His muscle biopsy showed Pompe's disease and had dolichoectasia of posterior circulation vessels. The other patient did not have any muscle weakness. Detailed workup for stroke in young was negative, but as angiogram showed intracranial vessel dolichoectasia, he was also investigated and found to have Pompe's disease. CONCLUSIONS AND RELEVANCE: We conclude that dolichoectasia of intracranial vessels in cases with stroke in young, with or without muscle weakness, should raise a differential of late onset Pompe's disease. This being one of the few treatable disorders makes the diagnosis all the more important.

Monitoring cardiac function by B-type natriuretic peptide (BNP) in patients with infantile Pompe's disease treated with recombinant alpha-glucosidase.

Infantile Pompe's disease is a glycogen storage disorder. Untreated it is lethal within the first year of life. Initial clinical trials with recombinant human acid alpha-glucosidase (rhGAA) have shown enzyme replacement therapy to improve cardiac and skeletal muscle function. B-type natriuretic peptide (BNP) is a neurohormone released by cardiac cells and increasingly used for monitoring heart failure in adults. We report on two infants affected by infantile Pompe's disease and treated with rhGAA, in whom cardiac function was supervised by BNP determination during the first 52 and 26 weeks of life, respectively. In the first patient, BNP (normal < 50 ng/l) increased from 475 (week 4) to 2417 ng/l (week 13) before, and declined continuously from 2696 (week 18) to 107 (week 52) after initiation of rhGAA-treatment. BNP-values reflected improvement of cardiac function earlier than echocardiography. In the second, earlier treated subject, BNP-values were only moderately elevated (86 ng/1) except two determinations timely linked to port implantation. In both patients, BNP levels correlated well with the severity of heart failure when using the NYHA classification modified for infants. These observations illustrate that BNP may be a valuable parameter for surveillance of cardiac function in Pompe's disease.

[Myopathy caused by acid maltase deficiency in an adult]. / Miopatía por déficit de maltasa ácida en el adulto.

We report a 46 years old male presenting with tetraparesis and severe respiratory involvement. He had moderately elevated serum creatine phosphokinase values and the electromyography showed myopathic alterations and irritative signs. In the muscle biopsy, a vacuolar myopathy with increased collagen deposits was found. Circulating lymphocytes presented abnormal PAS positive granules in their cytoplasm.

[Phosphofructokinase (PFK)].

This review is aimed to provide the up-to-date knowledge on phosphofructokinase (PFK), a key enzyme of glycolysis, with special references to the recent advances of molecular biology of the enzyme. In human, three isozymes named M (muscle), L (liver) and P (platelet) are identified. Recently, mRNA and gene structures of these isozymes have been clarified. Deficiency of PFK-M is characterized by muscle weakness due to fuel crisis in exercising muscles. Up to now, gene defects of PFK deficient patients have been sought in 38 alleles from Japanese, Ashkenazi Jewish, Non-Ashkenazi Italian, French Canadian and Swiss patients and molecular heterogeneity has been elucidated. Down syndrome, in which trisomy of chromosome 21 is known provides us an interesting gene-dosage effect on PFK-L isozyme. Other various pathologic states affecting PFK activity in vivo are also reviewed briefly.

[Pompe's disease--acid alpha-glucosidase deficiency--a review].

The importance of the role of acid alpha-glucosidase in the lysosomal degradation of glycogen has been emphasized because the deficiency of this enzyme in glycogenosis type II causes glycogen accumulation in lysosomes. Three clinical variants are distinguished. The infantile type has its onset shortly after birth and is known as generalized glycogen storage disease. The adult variant manifests itself mostly after the second decade of life and is characterized by progressive skeletal muscle weakness. The other is childhood type which is usually fatal by the second decade of life. Many biochemical reports of acid alpha-glucosidase have been published. Martiniuk et al reported the cDNA and amino acid sequence of human acid alpha-glucosidase. In prior studies, they reported that the lysosomal acid alpha-glucosidase was polymorphic with three alleles. The rarer allele GAA2 allozyme had a lower affinity for glycogen and starch. We also reported the enzyme heterogeneity in its affinity to Sephacryl S-200 gel. Whereby the enzyme separated into two fractions, S1 and S2. Each fraction contained 76 kDa and 67 kDa components on SDS/PAGE. The spleen enzyme consisted mainly of S1 fraction, containing only a 76 kDa component. In previous extensive studies, different mutations of Pompe's disease have been inferred from alterations in biochemical parameters. More recently Martiniuk et al, Hoefsloot et al and Van der Ploeg et al reported the analysis of cDNA and mRNA. These studies have revealed an absence or abnormal size of mRNA in large numbers of patients and altered restriction endonuclease fragments in a few patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Diagnóstico clínico-bioquímico de la enfermedad de Pompe

La enfermedad de Pompe es una de las glicogenosis o enferemdad de depósito del glucógeno, que se transmite con carácter autosómico recesivo y es producida por la deficiencia de la enzima maltasa ácida que degrada glicógeno en los lisosomas. Se dintinguen tres tipos de enferemdad de Pompe : el tipo infantil que se acracteriza por la acumulación de glicógeno en el hígado, músculo esquelético y cardíaco y células del sistema nervioso central; los pacientes fallecen usaulamente antes de los dos años por falla cardiorespiratoria; el fenotipo juvenil se presenta en niños o jóvenes, no siempre involucra el sistema nervioso central o el músculo cardíaco y los pacientes fallecen generalmente durante la segunda década de vida; el tipo adulto cursa con distrofia muscular, algunas veces asociada con deficiencia respiratoria por compromiso de los músculos diagragma e intercostales. El pronóstico depende del grado de la falla respiratoria, la cual es causa principal de la muerte de estos pacientes. En este trabajo se informa el caso de un niño de seis meses de edad, afectado por cardiomegalia, retardo psicomotor e hipotonía. La confirmación bioquímica de la enfermedad se hizo determinando la actividad de la alfa-glucosidasa en leucocitos por dos métodos diferentes, usando como sustrato maltasa o el sustrato fluorescente 4-metil-umbeliferil-glucósido. La actividad de la maltasa ácida en leucocitos, usando maltosa como sustrato fue de 6,36Umol glucosa/min/g, con un valor de referencia entre 16-63 Umoles/glucosa/min/g de proteína. Con el sustrato fluorogénico, la activida en el paciente fue de 34.48 nanomoles/h/mg, de proteína, para un valor de referencia entre 194 y 258. La actividad en leucocitos tanto del padre como de la madre corresponde a un 60 por ciento del valor normal, hallado en personas en cuya familia no se sospecha dicha enfermedad.