Botulinum neurotoxin serotype C: a novel effective botulinum toxin therapy in human Roberto Eleopra a, *, Valeria Tugnoli a , Ornella Rossetto b , Cesare Montecucco b , Domenico De Grandis a a Department of Neurology, Azienda Ospedaliera S.Anna, Corso Giovecca 203, 44100 Ferrara, Italy b Biomedical Science Department, University of Padua, Padua, Italy Received 3 January 1997; revised version received 12 February 1997; accepted 12 February 1997 Abstract Botulinum neurotoxin (BoNT) serotype A is commonly used in the treatment of focal dystonia. Nevertheless, some patients are or become resistant to this serotype. Consequently, other different serotypes have to be used. A comparison of the neuromuscular blockade induced by BoNT type A and C in the extensor digitorum brevis muscles of voluntary subjects was studied, by evaluating the amplitude variation over the time (until 90 days) of the compound muscular action potential elicited by supramaximal electrical stimulation of the peroneal nerve at the ankle. A very similar effect and temporal profile was observed for each serotype. On this basis, two patients with idiopathic facial hemispasm and one with blepharospasm were treated with BoNT serotype C with very beneficial long lasting effects.  1997 Elsevier Science Ireland Ltd. Keywords: Botulinum toxin C; Electrophysiology; Dystonia The therapeutic use of botulinum neurotoxin type A (BoNT/A) in humans is now well established and is rapidly expanding [5]. Parallel, there are reports of non-responder subjects [6,7]. These drawbacks can be overcome by using a different BoNT serotype and the therapeutic use of BoNT serotype F (BoNT/F) in patients with anti BoNT/A antibo- dies was recently described [3,8]. However, BoNT/F injec- tion in non-responders or in dystonic patients treated for the first time relieved symptoms for a shorter time period when compared to BoNT/A [8]. More recently BoNT serotype B (BoNT/B) injection was also proposed in clinical manage- ment [11], but an exact temporal profile of its efficacy has not appeared until now.Recently, the molecular lesions at the basis of the inhibition of neurotransmitter release caused by the seven BoNT serotypes, (indicated with letters from A to G) have been unraveled [9]. BoNTs are able to enter the neuronal cytosol, where they display a zinc-dependent pro- teinase activity, specific for three proteins of the neuroex- ocytosis apparatus. BoNT/B, BoNT/D, BoNT/F and BoNT/ G cleave at single points synaptobrevin (VAMP), a protein of the neurotransmitter containing small synaptic vesicles. BoNT/A and BoNT/E act specifically a different protein, called SNAP-25, whereas BoNT/C cleaves both SNAP-25 and syntaxin, two proteins located on the cytosolic face of the nerve plasmalemma [9]. BoNT/C is unique among botu- linum neurotoxins because it cleaves two, rather than one, proteins essential for neuroexocytosis. This double target specificity of BoNT/C suggested that it could be a valuable alternative to the use of BoNT/A and prompted us to eval- uate its therapeutic potential. We describe the electrophysiological results obtained with low dosage injection of BoNT/C in comparison with BoNT/A, in the extensor digitorum brevis (EDB) muscles of 15 human voluntary subjects. On this basis, we treated two patients affected by idiopathic facial hemispasm and one affected by blepharospasm with BoNT serotype C and dis- cuss the implication of these findings in the context of the clinical treatment. Fifteen voluntary subjects with no history of botulism and never treated before with any kind of BoNTs were exam- ined. All patients voluntarily entered in the study and gave their informed consent. The research was approved by our local Ethical Committee. Each subject was injected with 3 IU of Botox-Allergan (in 0.1 ml of saline solution) in the Neuroscience Letters 224 (1997) 91–94 0304-3940/97/$17.00  1997 Elsevier Science Ireland Ltd. All rights reserved PII S0304-3940(97)13448-6 * Corresponding author. Tel.: +39 532 295834; fax: +39 532 295588.