EPH receptor A4 (ephrin type-A receptor 4), also known as EphA4, belongs to the ephrin receptor subfamily of the protein tyrosine kinase family. Receptors in the EPH subfamily typically have a single kinase domain and an extracellular region containing a Cys-rich domain and 2 fibronectin type III repeats. Ephrin receptors are components of cell signalling pathways involved in animal growth and development, forming the largest sub-family of receptor tyrosine kinases (RTKs). Activation of EphA4 can cause myelin formation in the central nervous system and peripheral nervous system, which can inhibit neurotransmission and synaptic plasticity. At the same time, studies have shown that Epha4 can regulate the susceptibility of (motor) neurons to axonal degeneration, which may be a new target for therapeutic intervention.