Clinical, Neurological, and Genetic Characterization of Polyglucosan Body Myopathy Type 1 (PGBM1) in a Pediatrics Patient: Expanding the Spectrum of RBCK1-Related Disorders

Background Polyglucosan Body Myopathy Type 1 (PGBM1) is a rare autosomal recessive neuromuscular disorder caused by pathogenic variants in the RBCK1 gene. It is typically characterized by progressive myopathy, cardiomyopathy, and variable immune dysfunction. However, phenotypic variability, especially in the absence of immune abnormalities, has been increasingly recognized. This study aims to describe a pediatric case of PGBM1 with distinctive clinical features and no evidence of immune dysfunction. Methods A 17-year-old female, born to consanguineous parents (third-degree consanguinity), underwent detailed clinical, neurological, and genetic evaluation. The patient developed symptoms at eight years of age, and next-generation sequencing (NGS) were performed to confirm the molecular diagnosis. Results The patient exhibited progressive proximal limb and truncal weakness, bilateral ptosis, scapular winging, facial weakness, secondary amenorrhea, and cardiomyopathy, without any clinical or laboratory evidence of immune dysfunction. Genetic analysis revealed pathogenic variants in the RBCK1 gene, confirming the diagnosis of PGBM1. Notably, the absence of immune abnormalities contrasts with previously reported cases, emphasizing the phenotypic heterogeneity of PGBM1, even among individuals with similar genetic backgrounds. Conclusion This case expands the known phenotypic spectrum of PGBM1 and highlights the diagnostic complexity due to its variable clinical manifestations in pediatric patients. Early implementation of molecular genetic testing alongside a multidisciplinary clinical evaluation is crucial for accurate diagnosis, management, and genetic counseling. Ongoing documentation of such cases will enhance understanding of genotype–phenotype correlations in this rare neuromuscular disorder.