The goal of this Motor Neuron Disease (MND) Program Project Grant is to delineate principles underlying the selective vulnerability of the motor neuron. We plan to elucidate motor neuron-specific properties as well as factors that specifically act on motor neurons. The grant topics are: Core A - A clinical and pathological core that acts as a source of clinical information and specimens for members of the Program Project; the core also includes study of the characteristics of MND, the post- poliomyelitis syndrome, and medical ethical issues related to life- sustaining therapy in MND. Project #1 (Siddique) - An RFLP linkage study of familial MND. Project #3 (Gurney) - Neuroleukin (MND growth factor) and its relationship to MND survival and sprouting. Project #4 (Stefansson) Motor neuron-specific proteins and their relationship to motor neuron injury and neurite outgrowth. Project #5 (Roos) - Theiler's virus genes and gene products which determine neurotropism and neurovirulence.