In conclusion, this informative case demonstrates (1) the phenotypic variability of GM1 gangliosidosis type III; (2) that this condition should be considered in the differential diagnosis of juvenile-onset parkinsonism-dystonia, even without a skeletal phenotype; and (3) how awareness of the distinct MRI signs associated with a condition can accelerate clinical diagnosis. GM1-gangliosidosis type III associated parkinsonism. This case displays a complex early-onset neurological phenotype with cognitive decline, supranuclear ophthalmoplegia, anarthria associated with risus sardonicus, progressive parkinsonism-dystonia, and spasticity.1 Whilst acquired (hypoxic, infectious, toxic, neoplastic) causes should be considered, the positive family history of a similarly (but more mildly) affected sibling and relatives with parkinsonism strongly suggests a genetic etiology with possible autosomal recessive or mitochondrial inheritance. [Extracted from the article]