Novel mutations in the gene encoding acid α-1,4-glucosidase in a patient with late-onset glycogen storage disease type II (Pompe disease) with impaired intelligence

Limb-Girdle Muscular Dystrophies Classification and Therapies

Limb-girdle muscular dystrophies (LGMDs) are caused by mutations in multiple genes. This review article presents 39 genes associated with LGMDs. Some forms are inherited in a dominant fashion, while for others this occurs recessively. The classification of LGMDs has evolved through time. Lately, to be considered an LGMD, the mutation has to cause a predominant proximal muscle weakness and must be found in two or more unrelated families. This article also presents therapies for LGMDs, examining both available treatments and those in development. For now, only symptomatic treatments are available for patients. The goal is now to solve the problem at the root of LGMDs instead of treating each symptom individually. In the last decade, multiple other potential treatments were developed and studied, such as stem-cell transplantation, exon skipping, gene delivery, RNAi, and gene editing.

Case Report: Identification of Compound Heterozygous Mutations in a Patient With Late-Onset Glycogen Storage Disease Type II (Pompe Disease)

Pompe disease is an autosomal recessive hereditary lysosomal disorder and correlated with acid α-glucosidase enzyme (GAA) deficiencies, which lead to accumulation of glycogen in all tissues, most notably in skeletal muscles. Adult late-onset Pompe disease (LOPD) is a slowly progressive disease of proximal myopathy with later involvement of the respiratory muscles, resulting in respiratory failure. In this study, we reported a 22-year-old Chinese woman with inability to withstand heavy physical activity since childhood, who presented with respiratory and ambulation weakness in 2 months. On admission, her bilateral upper limbs strength was 4/5 and lower limbs strength was 3/5 according to Medical Research Council (MRC) score. The patient had compound heterozygotes containing a newly identified 4 nt deletion of coding sequence (deletion nt 1411_1414) in one of the acid α-glucosidase alleles and a c.2238G>C (p.Trp746Cys) missense mutation. This deletion has been reported in infant-onset Pompe disease (IOPD) but not LOPD. Intriguingly, this deletion mutation was not found in the patient's family and was considered as pathogenic. Muscle biopsy showed scattered vacuoles with basophilic granules inside the subsarcolemmal area, which were strongly stained by periodic acid-Schiff (PAS). Laboratory tests revealed a significant increase of creatine kinase MB isoenzyme (CK-MB) and lactate dehydrogenase (LDH). GAA level was 9.77 nmol/1 h/mg and was not sufficient for the diagnosis of GAA activity deficiency (0–3.78 nmol/1 h/mg). In summary, mutational analysis of GAA and muscle biopsy are crucial in the diagnosis of Pompe disease.

Two Approaches for a Genetic Analysis of Pompe Disease: A Literature Review of Patients with Pompe Disease and Analysis Based on Genomic Data from the General Population

In this study, two different approaches were applied in the analysis of the GAA gene. One was analyzed based on patients with Pompe disease, and the other was analyzed based on GAA genomic data from unaffected carriers in a general population genetic database. For this, GAA variants in Korean and Japanese patients reported in previous studies and in patients reported in the Pompe disease GAA variant database were analyzed as a model. In addition, GAA variants in the Korean Reference Genome Database (KRGDB), the Japanese Multi Omics Reference Panel (jMorp), and the Genome Aggregation Database (gnomAD) were analyzed. Overall, approximately 50% of the pathogenic or likely pathogenic variants (PLPVs) found in unaffected carriers were also found in real patients with Pompe disease (Koreans, 57.1%; Japanese, 46.2%). In addition, there was a moderate positive correlation (Spearman's correlation coefficient of 0.45-0.69) between the proportion of certain PLPVs in patients and the minor allele frequency of their variants in a general population database. Based on the analysis of general population databases, the total carrier frequency for Pompe disease in Koreans and Japanese was estimated to be 1.7% and 0.7%, respectively, and the predicted genetic prevalence was 1:13,657 and 1:78,013, respectively.

An emerging phenotype of central nervous system involvement in Pompe disease: from bench to bedside and beyond

Pompe disease (PD) is a lysosomal storage disorder caused by deficiency of the lysosomal enzyme acid-alpha glucosidase (GAA). Pathogenic variants in the GAA gene lead to excessive accumulation of lysosomal glycogen primarily in the cardiac, skeletal, and smooth muscles. There is growing evidence of central nervous system (CNS) involvement in PD. Current research is focused on determining the true extent of CNS involvement, its effects on behavior and cognition, and effective therapies that would correct the disease in both muscle and the CNS. This review article summarizes the CNS findings in patients, highlights the importance of research on animal models, explores the probable success of gene therapy in reversing CNS pathologies as reported by some breakthrough preclinical studies, and emphasizes the need to follow patients and monitor for CNS involvement over time. Lessons learned from animal models (bench) and from the literature available to date on patients will guide future clinical trials in patients (bedside) with PD. Our preliminary studies in infantile PD show that some patients are susceptible to early and extensive CNS pathologies, as assessed by neuroimaging and developmental assessments. This article highlights the importance of neuroimaging which could serve as useful tools to diagnose and monitor certain CNS pathologies such as white matter hyperintense foci (WMF) in the brain. Longitudinal studies with large sample sizes are warranted at this time to better understand the emergence, progression and consequences of CNS involvement in patients with PD.

Skeletal alterations, developmental delay and new mutations in juvenile-onset Pompe disease

Pompe disease is an autosomal recessive disorder caused by a deficiency of acid α-glucosidase. In addition to the severe infantile form with cardiac involvement, late-onset variants can affect older children, adolescents (aged >1 year old) or adults. Patients with juvenile (a subgroup of late-onset type) Pompe disease typically do not have cardiac alterations e.g. hypertrophic cardiomyopathy, and the diagnosis is often difficult because it can clinically resemble myriad other neuromuscular disorders. A high level of clinical suspicion is necessary for a timely and accurate diagnosis. We describe 3 interesting cases of patients with juvenile-onset Pompe disease who presented some uncommon clinical features e.g. skeletal alterations and developmental delay, and describe a new genetic variant. Juvenile-onset Pompe disease may be accompanied by uncommon clinical signs that could delay the diagnosis of Pompe disease due to the global pictures resembling other metabolic disorders.

Glycogen metabolism in humans

In the human body, glycogen is a branched polymer of glucose stored mainly in the liver and the skeletal muscle that supplies glucose to the blood stream during fasting periods and to the muscle cells during muscle contraction. Glycogen has been identified in other tissues such as brain, heart, kidney, adipose tissue, and erythrocytes, but glycogen function in these tissues is mostly unknown. Glycogen synthesis requires a series of reactions that include glucose entrance into the cell through transporters, phosphorylation of glucose to glucose 6-phosphate, isomerization to glucose 1-phosphate, and formation of uridine 5'-diphosphate-glucose, which is the direct glucose donor for glycogen synthesis. Glycogenin catalyzes the formation of a short glucose polymer that is extended by the action of glycogen synthase. Glycogen branching enzyme introduces branch points in the glycogen particle at even intervals. Laforin and malin are proteins involved in glycogen assembly but their specific function remains elusive in humans. Glycogen is accumulated in the liver primarily during the postprandial period and in the skeletal muscle predominantly after exercise. In the cytosol, glycogen breakdown or glycogenolysis is carried out by two enzymes, glycogen phosphorylase which releases glucose 1-phosphate from the linear chains of glycogen, and glycogen debranching enzyme which untangles the branch points. In the lysosomes, glycogen degradation is catalyzed by α-glucosidase. The glucose 6-phosphatase system catalyzes the dephosphorylation of glucose 6-phosphate to glucose, a necessary step for free glucose to leave the cell. Mutations in the genes encoding the enzymes involved in glycogen metabolism cause glycogen storage diseases.

A novel mutation of the GAA gene in a patient with adult-onset Pompe disease lacking a disease-specific pathology

We herein report a novel compound heterozygous mutation of the acid α-glucosidase (GAA) gene in a 23-year-old man with adult-onset Pompe disease. The patient was admitted for respiratory failure and a highly elevated serum level of creatine kinase (CK). His muscle pathology did not show typical vacuolated fibers; however, globular inclusion bodies with acid phosphatase (ACP) activity was observed. A molecular genetic analysis of the GAA gene revealed a novel compound heterozygous mutation, c.1544 T>A (M515K), combined with a previously reported mutation, c.1309 C>T (R437C). The presence of ACP-positive globular inclusion bodies is a useful diagnostic marker for adult-onset Pompe disease, even when typical vacuolated fibers are absent.