Huntington's disease presenting as posterior cortical atrophy.

mg (normal range 78-280), confirming the diagnosis of GM1 Gangliosidosis. Type 3 GM1 gangliosidosis is characterized by onset around the second decade of life with slowly progressive extrapiramidal signs, such as dystonia and parkinsonism. There is also a high prevalence of gait disturbance and dysarthria. Other symptoms are short stature, bone abnormalities, cognitive impairment, ataxia and cardiac disorders. Orofacial dystonia is a common feature of type 3 GM1 gangliosidosis, with a prevalence of 87.5% according to a recent report. Facial dystonia with proeminent involvement of oromandibular muscles is a frequent manifestation of neuroleptic induced movement disorders. However, there is also a number of dystonia syndromes in wich proeminet orofacial involvement occur, and their presence should alert the clinician to their possibility (Table). We suggest that in patients with early-onset dystonia, the occurance of facial grimacing should lead to the consideration of type 3 GM1 gangliosidosis, particularly when associated with speech and cognitive impairment, gait disturbances and bone abnormalities.