Abstract: Glycogen storage diseases (GSDs) are clinically and genetically heterogeneous disorders
that disturb glycogen synthesis or utilization. Although it is one of the oldest inherited metabolic
disorders, new genetic methods and long-time patient follow-ups provide us with unique insight
into the genotype–phenotype correlations. The aim of this study was to share the phenotypic
features and molecular diagnostic results that include new pathogenic variants in our GSD cases.
Twenty-six GSD patients were evaluated retrospectively. Demographic data, initial laboratory and
imaging features, and current findings of the patients were recorded. Molecular analysis results were
classified as novel or previously defined variants. Novel variants were analyzed with pathogenicity
prediction tools according to American College of Medical Genetics and Genomics (ACGM) criteria.
Twelve novel and rare variants in six different genes were associated with the disease. Hearing
impairment in two patients with GSD I, early peripheral neuropathy after liver transplantation in
one patient with GSD IV, epilepsy and neuromotor retardation in three patients with GSD IXA were
determined. We characterized a heterogeneous group of all diagnosed GSDs over a 5-year period in
our institution, and identified novel variants and new clinical findings. It is still difficult to establish
a genotype–phenotype correlation in GSDs.