The sodium channel beta 1 subunit is non-covalently associated with the pore-forming alpha-subunits, and has been proposed to act as a modulator of channel activity, regulator of channel cell surface expression and cell adhesion molecule. Its importance is evident since mutations of the beta 1 subunit cause neurologic and cardiovascular disorders. The first described beta 1 subunit mutation is the C121W, that is related to generalized epilepsy with febrile seizures plus (GEFS+), a childhood genetic epilepsy syndrome. This mutation changed a conserved cysteine residue in position 121 into a tryptophan, putatively disrupting a disulfide bridge that should normally maintain the beta 1 extracellular immunoglobulin-like fold. Using the 2-D-diagonal-SDS-PAGE technique, we demonstrated the existence of this putative disulfide bridge in the Ig-like extracellular domain of the beta 1 subunit and its disruption in the epileptogenic C121W mutant. (C) 2012 Elsevier Inc. All rights reserved.