Fast channel syndrome

Fast-channel syndrome. The clinical features resemble those of autoimmune myasthenia gravis (see below) with variable severity. Conversely to what is found in slow-channel syndrome, the open state of the AChR is destabilized, manifesting as fast dissociation of ACh from the receptor and/or excessively reduced open times. One mutation has also caused multiple congenital joint contractures owing to fetal hypomotility in utero. In most cases, the mutant allele causing the kinetic abnormality... 

The low-affinity fast channel syndrome is a rare, recessive condition where patients generally present with moderately severe myasthenic symptoms from birth (Uchitel et al 1993, Ohno et al 1996). Electrophysiologic studies revealed decremental CMAP and very small MEPPs. Single channel recordings from biopsied muscle endplate showed infrequent, abnormally brief openings in response to ACh. Morphologic studies demonstrated normal end plate structure, with normal number of AChR and no evidence of myopathy. 

Several groups have reported recessive, heteroaUelic mutations in the subunit gene in patients with nAChR deficiency or the low-affinity fast channel syndrome. 

Cdiannel problems 2, The acetylcholine receptor channel can also undergo mutation leading to fast-channel syndrome (I XIS). with clinical manifestations similar to those of slow-channel syndrome (S( S), What would the recordings of ion movement look like in this syndrome Suggest a biochemical explanation... 

With fast channel syndrome, the recordings would show channel events that are very brief, that is, with open channel lifetimes that are shorter than those of the control channels in problem 17. Possible explanations could include the converse of those in problem 17 quicker release of acetylcholine, a more rapid conformational transition horn the open state to the closed state, and/or other factors. 

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