Significance of early diagnosis and treatment of adult late-onset Pompe disease on the effectiveness of enzyme replacement therapy in improving muscle strength and respiratory function: a case report.

BACKGROUND: Pompe disease, a rare autosomal recessive disorder, is caused by mutations in the acid α-glucosidase gene. Pompe disease is a congenital metabolic disorder that affects all organs, particularly the striated muscle and nerve cells. Diagnosis is typically confirmed through enzyme assays that reveal reduced acid α-glucosidase activity. Enzyme replacement therapy utilizing human α-glucosidase is an available treatment option. Timely diagnosis and treatment in the early stages of the disease significantly impact the effectiveness of enzyme replacement therapy in enhancing patient condition. Here, we present a case of a patient with Pompe disease diagnosed 20 years after the onset of clinical symptoms. CASE PRESENTATION: A 38-year-old Iranian Baloch woman referred to our rheumatology clinic with progressive muscle weakness presents with a complex medical history. On mechanical ventilation for 12 years, she has endured fatigue and limb weakness since the age of 16, exacerbated following an abortion at 19. Despite undergoing corticosteroid and azathioprine therapies, the suspected diagnosis of inflammatory myopathy did not yield improvement. Hospitalization at 23 due to respiratory failure post-pregnancy led to her continued reliance on a ventilator. A dried blood spot test indicated reduced GAA enzyme activity, confirming a diagnosis of Pompe disease through genetic testing. Treatment with myozyme for 2 years demonstrated limited efficacy, as the patient experienced improved breathing but no significant overall improvement in limb-girdle muscular weakness. This case underscores the challenges and complexities involved in diagnosing and managing rare neuromuscular disorders like Pompe disease. CONCLUSION: Early intervention with enzyme replacement therapy plays a crucial role in halting further muscle loss and disease progression in Pompe disease patients. It is important to note that treatment during advanced stages of the disease may not yield substantial benefits. Nevertheless, enzyme instability and denaturation due to temperature and neutral pH levels, along with limited delivery to disease-relevant tissues, can pose challenges in treatment. However, timely diagnosis of Pompe disease is paramount for its effective management and improved outcomes.

Unusual presentation of PYGM gene mutation as late-onset McArdle disease with camptocormia: a case report.

BACKGROUND: Glycogen storage disease type 5 (McArdle disease) leads to a deficiency in the activity of myophosphorylase resulting in an impaired glucose utilization. The disease can be caused by a variety of mutations in the PYGM gene, and its typical clinical manifestation is muscles weakness within the first three decades of life. CASE PRESENTATION: In this case report we present the diagnostic work-up of a physically active 78-year-old Caucasian patient suffering from a 2-year history of progressive camptocormia including clinical, radiologic, histological, and genetic tests. There was no history of neuro-muscular diseases in the family. Serum CK levels were moderately increased while other blood/urine parameters were normal. Magnetic resonance imaging showed fatty remodeling of the muscles of the back. Histochemical examination of a muscle biopsy revealed the absence of myophosphorylase activity, while gene analysis identified a known early-onset McArdle mutation in the PYGM gene. CONCLUSION: This case highlights that the clinical spectrum of PYGM gene mutation typically manifest during adolescence, but it is also a differential diagnosis in late onset muscle disorders and emphases the investigation of the role of ACE inhibitors in this disease.

Continuous glucose monitoring metrics in people with liver glycogen storage disease and idiopathic ketotic hypoglycemia: A single-center, retrospective, observational study.

BACKGROUND: Cohort data on continuous glucose monitoring (CGM) metrics are scarce for liver glycogen storage diseases (GSDs) and idiopathic ketotic hypoglycemia (IKH). The aim of this study was to retrospectively describe CGM metrics for people with liver GSDs and IKH. PATIENTS AND METHODS: CGM metrics (descriptive, glycemic variation and glycemic control parameters) were calculated for 47 liver GSD and 14 IKH patients, categorized in cohorts by disease subtype, age and treatment status, and compared to published age-matched CGM metrics from healthy individuals. Glycemic control was assessed as time-in-range (TIR; ≥3.9 - ≤7.8 and ≥3.9 - ≤10.0 mmol/L), time-below-range (TBR; <3.0 mmol/L and ≥3.0 - ≤3.9 mmol/L), and time-above-range (TAR; >7.8 and >10.0 mmol/L). RESULTS: Despite all patients receiving dietary treatment, GSD cohorts displayed significantly different CGM metrics compared to healthy individuals. Decreased TIR together with increased TAR were noted in GSD I, GSD III, and GSD XI (Fanconi-Bickel syndrome) cohorts (all p < 0.05). In addition, all GSD I cohorts showed increased TBR (all p < 0.05). In GSD IV an increased TBR (p < 0.05) and decreased TAR were noted (p < 0.05). In GSD IX only increased TAR was observed (p < 0.05). IKH patient cohorts, both with and without treatment, presented CGM metrics similar to healthy individuals. CONCLUSION: Despite dietary treatment, most liver GSD cohorts do not achieve CGM metrics comparable to healthy individuals. International recommendations on the use of CGM and clinical targets for CGM metrics in liver GSD patients are warranted, both for patient care and clinical trials.

Neuromuscular junction dysfunction in a mouse model of Lafora disease.

Lafora disease (LD), a fatal neurodegenerative disorder, is caused by mutations in the EPM2A gene coding laforin phosphatase or NHLRC1 gene coding malin ubiquitin ligase. The LD symptoms include epileptic seizures, ataxia, dementia, and cognitive decline. Studies on LD have primarily concentrated on the pathophysiology in the brain. A few studies have reported motor symptoms, muscle weakness and muscle atrophy. Intriguingly, skeletal muscles are known to accumulate Lafora polyglucosan bodies. Using Laforin-deficient mice, an established model for LD, we demonstrate that LD pathology correlated with structural and functional impairments in the neuromuscular junction (NMJ). Specifically, we find impairment in the NMJ transmission, which coincides with altered expression of NMJ-associated genes and reduced motor endplate area, fragmented junctions and loss of fully innervated junctions at NMJ. We also observe a reduction of alpha motor neurons in the lumbar spinal cord, with significant presynaptic morphological alterations. Disorganized myofibrillar patterns, slight z-line streaming, and muscle atrophy are also evident in LD animals. In summary, our study offers novel insight into the neuropathic and myopathic alterations leading to motor deficits in LD.

Glycogen metabolism and structure: A review.

Glycogen is a glucose polymer that plays a crucial role in glucose homeostasis by functioning as a short-term energy storage reservoir in animals and bacteria. Abnormalities in its metabolism and structure can cause several problems, including diabetes, glycogen storage diseases (GSDs) and muscular disorders. Defects in the enzymes involved in glycogen synthesis or breakdown, resulting in either excessive accumulation or insufficient availability of glycogen in cells seem to account for the most common pathogenesis. This review discusses glycogen metabolism and structure, including molecular architecture, branching dynamics, and the role of associated components within the granules. The review also discusses GSD type XV and Lafora disease, illustrating the broader implications of aberrant glycogen metabolism and structure. These conditions also impart information on important regulatory mechanisms of glycogen, which hint at potential therapeutic targets. Knowledge gaps and potential future research directions are identified.

[Onset of Glycogen Storage Disease Type â « in Two Brothers in the Neonatal Period].

Glycogen storage diseases (GSDs) are a group of autosomal recessive disorders of glucose metabolism.GSDs are caused by congenital deficiency of enzymes in glycogen synthesis or decomposition,which results in glycogen accumulation in organs.According to the types of enzyme deficiency,GSDs can be classified into more than ten types,among which GSD Ⅻ is a super-rare type of GSD.Two brothers with a 5-year age difference presented severe neonatal asphyxia,myasthenia,myocardial damage,anemia,and mental retardation,being GSD Ⅻ homozygous cases with neonatal onset.The results of gene detection showed that nucleotide and amino acid alterations (c.619G>A,p.E207K) of the ALDOA gene existed in the two brothers,being homozygous,and the genotypes in the parents were heterozygous.This article summarized the clinical features,diagnosis,and treatment of GSD Ⅻ,providing reference for exploring the etiology and treatment of severe asphyxia,myasthenia,anemia,and multiple organ damage in neonates after birth.

McArdle's Disease: A Differential Diagnosis of Metabolic Myopathies.

McArdle's disease, also known as glycogen storage disease type V or McArdle syndrome, is a pure muscle myopathy with an autosomal recessive inheritance pattern. It is caused by mutations in the gene that encodes muscle phosphorylase. Symptoms typically begin in late adolescence or early adulthood, presenting as exercise intolerance. This review focuses on the diagnosis of McArdle's disease, initially manifesting as a clinical picture of rhabdomyolysis in an 18-year-old male patient with a history of minor thalassemia who had been followed in pediatric consultation since age three for failure to thrive. After excluding common causes such as alcohol consumption, drug use, traumatic muscle compression, and other conditions, the diagnosis of McArdle's disease was considered. The diagnosis was supported by laboratory tests showing myoglobinuria and elevated creatine kinase levels, as well as the absence of increased serum lactate following ischemic exercise. Genetic testing confirmed the presence of mutations in the PYGM gene, corroborating the diagnosis. Treatment includes administering a diet rich in slow-absorbing carbohydrates, regular low-intensity physical exercise, and, in some cases, supplementation with vitamin B6 and creatine. The prognosis is generally favorable with proper disease management, although vigorous exercise should be avoided to prevent complications such as severe muscle injury and rhabdomyolysis. Although McArdle's disease is a rare condition, it is likely underdiagnosed. Ideally, it should be considered in the differential diagnosis of rhabdomyolysis in all patients with symptoms of exercise intolerance and/or recurrent myoglobinuria.

New perspectives for the treatment and follow-up of glycogen storage disease type V: DL-3-hydroxybutyric acid with modified Atkins diet and quadriceps femoris shear wave elastography.

OBJECTIVES: Glycogen storage disease type V is caused by the mutations in muscle glycogen phosphorylase gene. This is the first report which DL-3-hydroxybutyric acid was used in combination with modified Atkins diet for the treatment of a patient with glycogen storage disease type V and quadriceps femoris shear wave elastography was performed to evaluate the treatment efficacy. CASE PRESENTATION: A 13-year-old girl was referred with fatigue and muscle cramps with exercise and there were no pathological findings in physical examination. Creatine kinase levels with 442 U/L. No phosphorylase enzyme activity was detected in muscle biopsy, a homozygous c.1A>G (p.M1V) pathogenic mutation was found in PYGM gene. She was started on DL-3-hydroxybutyric acid and modified Atkins diet at age 16. Her walking and stair climbing capacity increased, the need for rest during exercise decreased. The stiffness of the quadriceps femoris exhibited a reduction. CONCLUSIONS: DL-3-hydroxybutyric acid and modified Atkins diet may provide an alternative fuel and shear wave elastography may be useful in demonstrating treatment efficacy. More clinical and pre-clinical studies are obviously needed to reach more definite conclusions.

The Autophagic Activator GHF-201 Can Alleviate Pathology in a Mouse Model and in Patient Fibroblasts of Type III Glycogenosis.

Glycogen storage disease type III (GSDIII) is a hereditary glycogenosis caused by deficiency of the glycogen debranching enzyme (GDE), an enzyme, encoded by Agl, enabling glycogen degradation by catalyzing alpha-1,4-oligosaccharide side chain transfer and alpha-1,6-glucose cleavage. GDE deficiency causes accumulation of phosphorylase-limited dextrin, leading to liver disorder followed by fatal myopathy. Here, we tested the capacity of the new autophagosomal activator GHF-201 to alleviate disease burden by clearing pathogenic glycogen surcharge in the GSDIII mouse model Agl-/-. We used open field, grip strength, and rotarod tests for evaluating GHF-201's effects on locomotion, a biochemistry panel to quantify hematological biomarkers, indirect calorimetry to quantify in vivo metabolism, transmission electron microscopy to quantify glycogen in muscle, and fibroblast image analysis to determine cellular features affected by GHF-201. GHF-201 was able to improve all locomotion parameters and partially reversed hypoglycemia, hyperlipidemia and liver and muscle malfunction in Agl-/- mice. Treated mice burnt carbohydrates more efficiently and showed significant improvement of aberrant ultrastructural muscle features. In GSDIII patient fibroblasts, GHF-201 restored mitochondrial membrane polarization and corrected lysosomal swelling. In conclusion, GHF-201 is a viable candidate for treating GSDIII as it recovered a wide range of its pathologies in vivo, in vitro, and ex vivo.

Long-term observation of patients with advanced late-onset Pompe disease undergoing enzyme replacement therapy: A 15-year observation in a single center.

BACKGROUND: There have been few descriptions in the literature on long-term enzyme replacement therapy (ERT) in patients with advanced late-onset Pompe disease (LOPD). OBJECTIVES: This study aimed to assess the efficacy and limitations of ERT in advanced LOPD patients. METHODS: We retrospectively reviewed the clinical courses of patients with advanced LOPD (two juvenile-onset and five adult-onset patients) who were treated with recombinant human alglucosidase alfa to examine improvements achieved with and limitations of ERT until their death or when switching to avalglucosidase alfa occurred. RESULTS: All patients were non-ambulant and ventilator dependent. The duration of follow-up ranged from 3.7 to 15.0 years (median 9.0 years). All patients reported improvements in their lives during the first two or three years of ERT. Vital capacity was clearly improved in patients with relatively spared respiratory function, although it deteriorated after respiratory complications such as pneumothorax. Pinch and grip power tended to be preserved during the treatment period. Muscle CT revealed progression of atrophy and fatty replacement predominantly in the proximal limb muscles without improvement after ERT. Four patients died due to aspergillosis, respiratory failure, ileus, and sudden death of unknown cause. CONCLUSIONS: Our findings demonstrate that patients undergoing ERT show certain improvements, even in the advanced stage of Pompe disease. Respiratory complications are lethal even during ERT, and early diagnosis and induction of therapy are critical. Muscle wasting progressed more severely in the proximal limbs, even after ERT.

[Juvenile Pompe disease: Undescribed genotype. First report in Quintana Roo]. / Enfermedad de Pompe juvenil: genotipo no descrito. Primer reporte en Quintana Roo.

Background: Pompe disease (PD) is a rare autosomal recessive genetic disorder (1 in 14,000) which affects the synthesis of acid alpha-glucosidase (AGA), leading to intralysosomal glycogen accumulation in muscle tissue. The clinical presentation is heterogeneous, with variable degrees of involvement and progression, classifiable based on the age of onset into infantile (classic or non-classic) and late-onset forms (juvenile or adult). The diagnostic test of choice is the enzymatic analysis of AGA, and the only pharmacological treatment is enzyme replacement therapy (ERT). This document aims to report a clinical case of late-onset PD. Clinical case: 14-year-old male who started at the age of 5 with postural alterations, gait changes, and decreased physical performance compared to his peers. A diagnostic evaluation was initiated in 2022 due to worsening neuromuscular symptoms, accompanied by dyspnea, tachycardia, and chest pain. A suspicion of a lysosomal storage myopathy was established, and through enzymatic determination of AGA the diagnosis of PD was confirmed. The study of the GAA gene revealed the association of 2 previously unreported genomic variants. ERT was initiated, resulting in clinical improvement. Conclusions: The age of symptom onset, severity of clinical presentation, and prognosis of the disease depend on the specific mutations involved. In this case, the identified genetic alterations are associated with different phenotypes. However, based on the clinical presentation, it is categorized as juvenile PD with an indeterminate prognosis.

Introducción: la enfermedad de Pompe (EP) es un padecimiento genético autosómico recesivo poco frecuente (1:14,000) que afecta la síntesis de alfa-glucosidasa ácida (AGA) y condiciona un depósito de glucógeno intralisosomal en tejido muscular. La presentación clínica es heterogénea, con grados variables de afectación y progresión, clasificable según la edad de aparición en infantil (clásica y no clásica) y de inicio tardío (juvenil o de adultez). La prueba diagnóstica de elección es el análisis enzimático de AGA y el único tratamiento farmacológico es la terapia de reemplazo enzimático (TRE). Este documento tiene como objetivo reportar un caso clínico de EP de inicio tardío. Caso clínico: paciente de sexo masculino de 14 años que comenzó a los 5 años con alteraciones de la postura, marcha y desempeño físico. Se inició protocolo de estudio ante agravamiento de los síntomas neuromusculares, a los que se agregaron disnea, taquicardia y dolor torácico. Se sospechó de una miopatía metabólica de depósito lisosomal y mediante determinación enzimática de AGA se confirmó el diagnóstico de EP. El estudio molecular del gen GAA reportó una asociación de 2 variantes genómicas no descritas previamente. Se empleó la TRE con mejoría clínica. Conclusiones: la edad de inicio del cuadro clínico, severidad y pronóstico dependen de las mutaciones presentadas. En este caso, las alteraciones genéticas encontradas están relacionadas con diferentes fenotipos; no obstante, por clínica es categorizado como una EP juvenil con pronóstico indeterminado.

Case report: Comprehensive exploration of a novel PFKM mutation in glycogen storage disease Type VII.

Glycogen Storage Disease Type VII (GSD VII) is a rare glycogen metabolism disorder resulting from mutations in the PFKM gene, inherited in an autosomal recessive manner. It is characterized by exercise intolerance, muscle cramps, myoglobinuria, compensatory hemolysis, and later onset de novo myasthenia and mild myopathy, contributing to its clinical heterogeneity and diagnostic challenges. Here, we report a rare case of a 17-year-old Chinese woman exhibiting substantial muscle weakness and compensated hemolysis. Muscle biopsies showed glycogen deposition, and blood tests showed hyperuricemia and significantly elevated creatine kinase. Whole genome sequencing (WGS) and whole exome sequencing (WES) identified two compound heterozygous mutations in the PFKM (NM_000289.6) gene: c.626G>A and c.1376G>A in exons 7 and 15, respectively. According to the clinical presentation, diagnostic examination, and WES results, the patient was finally diagnosed with GSDVII. The discovery of these two new PFKM mutations expands the genetic spectrum, and understanding the clinical manifestations of these mutations is critical to preventing diagnostic delays and timely intervention and treatment.

A Functional Human Glycogen Debranching Enzyme Encoded by a Synthetic Gene: Its Implications for Glycogen Storage Disease Type III Management.

BACKGROUND: Glycogen Storage Disease type III (GSD III) is a metabolic disorder resulting from a deficiency of the Glycogen Debranching Enzyme (GDE), a large monomeric protein (approximately 170 kDa) with cytoplasmic localization and two distinct enzymatic activities: 4-α-glucantransferase and amylo-α-1,6-glucosidase. Mutations in the Agl gene, with consequent deficiency in GDE, lead to the accumulation of abnormal/toxic glycogen with shorter chains (phosphorylase limit dextrin, PLD) in skeletal and/or heart muscle and/or in the liver. Currently, there is no targeted therapy, and available treatments are symptomatic, relying on specific diets. METHODS: Enzyme Replacement Therapy (ERT) might represent a potential therapeutic strategy for GSD III. Moreover, the single-gene nature of GSD III, the subcellular localization of GDE, and the type of affected tissues represent ideal conditions for exploring gene therapy approaches. Toward this direction, we designed a synthetic, codon-optimized cDNA encoding the human GDE. RESULTS: This gene yielded high amounts of soluble, enzymatically active protein in Escherichia coli. Moreover, when transfected in Human Embryonic Kidney cells (HEK-293), it successfully encoded a functional GDE. CONCLUSION: These results suggest that our gene or protein might complement the missing function in GSD III patients, opening the door to further exploration of therapeutic approaches for this disease.

Potential use of other starch sources in the treatment of glycogen storage disease type Ia - an in vitro study.

BACKGROUND: Glycogen storage disease type Ia (GSD-Ia) is one of the most common hepatic GSD. Its treatment mainly consists of a diet including a high intake of slow-digestion carbohydrates such as raw cornstarch and the restriction of simple sugars. This enables the maintenance of euglycemia and prevents secondary metabolic disorders. Starch is a glucose polymer formed by amylose and amylopectin, which can be obtained from distinct sources. Although uncooked cornstarch has been successfully used in the treatment of GSD-Ia, it can lead to hyperglycemia and weight gain. in vitro andin vivo tests indicated that sweet manioc starch can be potentially used in the treatment of GSD-Ia. RESULTS: The moisture analysis revealed a variation from 10.3 to 12.8% in the sweet manioc starch samples, whereas the moisture content of uncooked cornstarch ranged from 7.3 to 11.1%. Quantifiable sugar was detected in 3/5 samples of sweet manioc starch and 1/3 samples of uncooked cornstarch. Notably, this uncooked cornstarch brand is widely employed in GSD-Ia treatment in Brazil. Products B and E had higher values of amylopectin and undetectable levels of sugars. A clinical trial is warranted to compare samples F and G and determine the impact of sugar trace in the same dietary source of starch. CONCLUSIONS: Collectively, the results demonstrated possible therapeutic alternatives for GSD-Ia in addition to traditional uncooked cornstarch.

Decoding the muscle transcriptome of patients with late onset Pompe disease reveals markers of disease progression.

Late-onset Pompe Disease (LOPD) is a rare genetic disorder caused by the deficiency of acid alpha-glucosidase leading to progressive cellular dysfunction due to the accumulation of glycogen in the lysosome. The mechanism of relentless muscle damage - a classic manifestation of the disease - has been extensively studied by analysing the whole muscle tissue; however, little, if any, is known about transcriptional heterogeneity among nuclei within the multinucleated skeletal muscle cells. This is the first report of application of single nuclei RNA sequencing to uncover changes in the gene expression profile in muscle biopsies from eight patients with LOPD and four muscle samples from age and gender matched healthy controls. We matched these changes with histology findings using GeoMx Spatial Transcriptomics to compare the transcriptome of control myofibers from healthy individuals with non-vacuolated (histologically unaffected) and vacuolated (histologically affected) myofibers of LODP patients. We observed an increase in the proportion of slow and regenerative muscle fibers and macrophages in LOPD muscles. The expression of the genes involved in glycolysis was reduced, whereas the expression of the genes involved in the metabolism of lipids and amino acids was increased in non-vacuolated fibers, indicating early metabolic abnormalities. Additionally, we detected upregulation of autophagy genes, and downregulation of the genes involved in ribosomal and mitochondrial function leading to defective oxidative phosphorylation. The upregulation of the genes associated with inflammation, apoptosis and muscle regeneration was observed only in vacuolated fibers. Notably, enzyme replacement therapy - the only available therapy for the disease - showed a tendency to restore metabolism dysregulation, particularly within slow fibers. A combination of single nuclei RNA sequencing and spatial transcriptomics revealed the landscape of normal and the diseased muscle, and highlighted the early abnormalities associated with the disease progression. Thus, the application of these two new cutting-edge technologies provided insight into the molecular pathophysiology of muscle damage in LOPD and identified potential avenues for therapeutic intervention.

Screening and surveillance of hepatocellular carcinoma by serum des-gamma-carboxy prothrombin in patients with glycogen storage disease type Ia.

No sensitive tumor marker for hepatocellular carcinoma (HCC) is available for patients with glycogen storage disease type Ia (GSDIa), in whom alpha-fetoprotein and carcino-embryonic antigen levels often remain normal. We describe increased levels of the HCC tumor marker des-gamma-carboxy prothrombin (DCP) in GSDIa patients with HCC. In one case DCP levels normalized after liver transplantation. We recommend including DCP as a screening HCC tumor marker in the surveillance of patients with GSDIa.

Gut Dysbiosis Drives Inflammatory Bowel Disease Through the CCL4L2-VSIR Axis in Glycogen Storage Disease.

Patients with glycogen storage disease type Ib (GSD-Ib) frequently have inflammatory bowel disease (IBD). however, the underlying etiology remains unclear. Herein, this study finds that digestive symptoms are commonly observed in patients with GSD-Ib, presenting as single or multiple scattered deep round ulcers, inflammatory pseudo-polyps, obstructions, and strictures, which differ substantially from those in typical IBD. Distinct microbiota profiling and single-cell clustering of colonic mucosae in patients with GSD are conducted. Heterogeneous oral pathogenic enteric outgrowth induced by GSD is a potent inducer of gut microbiota immaturity and colonic macrophage accumulation. Specifically, a unique population of macrophages with high CCL4L2 expression is identified in response to pathogenic bacteria in the intestine. Hyper-activation of the CCL4L2-VSIR axis leads to increased expression of AGR2 and ZG16 in epithelial cells, which mediates the unique progression of IBD in GSD-Ib. Collectively, the microbiota-driven pathomechanism of IBD is demonstrated in GSD-Ib and revealed the active role of the CCL4L2-VSIR axis in the interaction between the microbiota and colonic mucosal immunity. Thus, targeting gut dysbiosis and/or the CCL4L2-VISR axis may represent a potential therapy for GSD-associated IBD.

Phenotypic and genotyping spectrum of two Iranian cases with RBCK1-associated polyglucosan body myopathy.

Glycogen storage diseases (GSDs) are a group of metabolic disorders affecting glycogen metabolism, with polyglucosan body myopathy type 1 (PGBM1) being a rare variant linked to RBCK1 gene mutations. Understanding the clinical diversity of PGBM1 aids in better characterization of the disease. Two unrelated Iranian families with individuals exhibiting progressive muscle weakness underwent clinical evaluations, genetic analysis using whole exome sequencing (WES), and histopathological examinations of muscle biopsies. In one case, a novel homozygous RBCK1 variant was identified, presenting with isolated myopathy without cardiac or immune involvement. Conversely, the second case harbored a known homozygous RBCK1 variant, displaying a broader phenotype encompassing myopathy, cardiomyopathy, inflammation, and immunodeficiency. Histopathological analyses confirmed characteristic skeletal muscle abnormalities consistent with PGBM1. Our study contributes to the expanding understanding of RBCK1-related diseases, illustrating the spectrum of phenotypic variability associated with distinct RBCK1 variants. These findings underscore the importance of genotype-phenotype correlations in elucidating disease mechanisms and guiding clinical management. Furthermore, the utility of next-generation sequencing techniques in diagnosing complex neurogenetic disorders is emphasized, facilitating precise diagnosis and enabling tailored genetic counseling for affected individuals and their families.