Gylcogen storage disease (GSD-PGBM1)

Glycogen storage diseases (GSDs) are a rare group of inherited metabolic disorders characterized by defects in specific enzymes responsible for glycogen synthesis, degradation, or regulation. These enzymatic deficiencies lead to abnormal glycogen accumulation, particularly in tissues with high glycogen turnover such as the liver, cardiac muscle, skeletal muscle, and smooth muscle.

In the Basset Hound breed, a genetic variant in the RBCK1 gene has been identified to be associated with a glycogen storage disease. The RBCK1 gene encodes a subunit of an E3 ubiquitin ligase involved in inflammatory and immune responses. Deficiency of this protein results in the accumulation of abnormal glycogen in the form of polyglucosan bodies. In humans, several genetic variants in RBCK1 are associated with polyglucosan body myopathy type 1 (PGBM1), a form of GSD characterized by skeletal muscle myopathy, cardiomyopathy, and polyglucosan accumulation.

Affected Basset Hounds typically develop gastrointestinal problems such as chronic vomiting and diarrhea beginning between 8 months and one year of age. In later stages (around three years of age), dogs exhibit progressive muscle weakness, exercise intolerance, congestive heart failure, and may experience sudden death.

While early clinical signs are subtle (often limited to mildly elevated CK levels), later stages show measurable increases in CK, AST, and cardiac troponin, indicating ongoing cardiac damage. Postmortem histopathological examination reveals extensive glycogen accumulation in the heart, leading to severe myocardial degeneration and necrosis, as well as glycogen deposition in smooth muscle, particularly within the gastrointestinal tract.