EphA4 is a member of the Eph receptor tyrosine kinase family and has important functions in the developing and adult nervous system (PMID: 14697664). The Eph receptors comprise a large family of closely related transmembrane tyrosine kinases that actively signal when bound to their ephrin ligands. The Eph receptors are characterized by an extracellular region with a unique cysteine-rich motif extending over its amino-terminal half, followed by two fibronectin type III motifs (PMID: 9530499). They are divided into two sub-groups (EphA and EphB) based on the similarity of their extracellular domain sequences and their affinities for binding ephrin-A and ephrin-B ligands (PMID: 11114742). EphA4 is involved in commissure formation within the forebrain, axonal guidance in the corticospinal tract, regulation of the central pattern generator that provides normal locomotor function and axonal regeneration following spinal cord injury (PMID: 30061574). EphA4 has been implicated as a disease modifier of amyotrophic lateral sclerosis (ALS) (PMID: 22922411).