Familial amyotrophic lateral sclerosis (FALS), 'pure' hereditary spastic paraparesis (HSP) and primary lateral sclerosis (PLS) are genetically heterogeneous disorders caused by motor neuron degeneration. These disorders either affect, both the upper and lower motor neurons (FALS), or primarily the upper motor neuron (HSP and PLS). The long-term goal of my laboratory is to identify the genetic contribution to the pathogenesis of these disorders. Success in this goal will lead to the formulation of interventions based on disease mechanisms to prevent, postpone and treat these and related disorders. We now plan to build on the work we accomplished in the last five years as part of a program project (NS 21442). We fulfilled all the Specific Aims such that we identified the ALSIN gene, that cause both recessive FALS (ALS2) and recessive juvenile PLS (JPLS1), on chromosome 2q33, studied mutations in SPASTIN that cause HSP (SPG5), and identified new loci for dominant ALS (on the X-chromosome) and ALS/dementia on chromosome 9q21-q22. We will further expand our gene discovery effort in recessive ALS and recessive HSP develop genetic models of FALS, JPLS, and HSP, and interrogate the products of causative genes for their protein-protein interactions to trace their signaling pathways. We plan to accomplish these goals by three main Specific Aims (1) Identify the genes for a more common form of recessive FALS (ALS5) on chromosome 15q15-q21 and a common form of recessive HSP (SPG5A) on chromosome 8q. (2) Develop genetic models of alsin for the JPLS and ALS phenotypes and of spastin for the HSP phenotype (SPG4). (3) Identify protein interactions of alsin. In the previous period we narrowed the loci for ALS5 and SPG5A. We will use high throughput sequencing and bioinformatic support to identify these genes, as we successfully did the case of the ALS2 gene. We will make knockout models for alsin and spastin, to study the pathology and pathogenesis of these disorders. Finally, the interacting partner proteins of alsin and subsequently of spastin will be interrogated by the two-hybrid systems and immunoprecipitation. Interaction will be confirmed by dual labeled confocal microscopy and FRET analysis.