Abstract
We report the case of a patient presenting with diplopia, ptosis, and blurred vision who was found to have a heterozygous SQSTM1 gene variant (c.1175C>T) following electrophysiological evidence of a postsynaptic neuromuscular junction disorder. The patient had negative antibody testing, mildly elevated creatine phosphokinase (CPK), and abnormal organic acid analysis. Repetitive nerve stimulation demonstrated a decremental response consistent with impaired postsynaptic transmission. Given the atypical presentation and systemic findings, genetic testing was pursued, revealing a variant of uncertain significance in SQSTM1, despite the variant being classified as pathogenic in genetic databases. This case raises the possibility of a broader neuromuscular phenotype associated with SQSTM1 mutations and underscores the value of genetic testing in seronegative neuromuscular disorders. It also highlights the need to consider SQSTM1 variants in the differential diagnosis of seronegative neuromuscular presentations.