L1CAM and L1 syndrome: The experimental, high REST PC12 cell model we have characterized could be used for the investigation of additional properties of L1CAM, important also for the pathology of the L1 syndrome, including the characterization of the interaction of L1CAM with the TrkA receptor, the mechanism of its coreceptor effect, and the putative defects of the interaction and modulation of TrkA typical of various L1CAM mutants.