A PATIENT WITH ADULT ONSET GM2-GANGLIOSIDOSIS: 24 YEARS OF FOLLOW-UP Scarpelli M 1 , Tomelleri G 1 , Bertolasi L 1 , Salviati A 1 1 Dep Neurol, Univ of Verona, verona, Italy Sandhoff disease is a lipid-storage disorder caused by a defect in ganglioside metabolism due to mutations in the HEXB gene that disrupt the function of the N-acetyl-beta-D-glucosaminidase isoforms Hex A and Hex B. A late-onset form of Sandhoff disease is rare and its symptoms are heterogeneous, including cerebellar syndrome, motor neuron disease and autonomic dysfunction. We report on a 25 year-old man who suffered from mild proximal lower limb muscle weakness (4 MRC) and intense fasciculations. EMG demonstrated signs of denervation in lower limbs, whereas brain MRI was normal. Biochemical studies documented a 13% residual Hex activity in leukocytes; HEXB genetic analysis revealed a compound: delta5' deletion and C1214T (Pro405Leu) missense mutation. Twenty years later appeared bilateral Babinski sign and neurophysiological study showed peripheral sensory neuropathy. Twenty-four years from the onset, he was independent in deambulation, his weakness in lower limbs is slightly worsened (3 MRC) and mild weakness appeared in both arms. He didn't develop neither cerebellar or autonomic signs and brain MRI remained normal. To our knowledge, this is the longest follow-up in a patient with Sandhoff disease. It underlines how a clinical history of pure motor neuron disorder, in GM2-gangliosidosis, may have a relative benign course.