Leucine-rich repeat transmembrane neuronal protein 4, also known as LRRTM4, is a single-pass type I  membrane protein which belongs to the LRRTM family. LRRTM4 is expressed in the limb mesenchyme, neural tube, caudal mesoderm and in three distinct regions of the head. LRRTM4 may play a role in the development and maintenance of the vertebrate nervous system. Leucine-rich repeat containing proteins are involved in protein-protein interactions and they regulate numerous cellular events during nervous system development and disease. Human and mouse LRRTMs are highly conserved, and orthologous genes exist in other vertebrates but not in invertebrates. LRRTM mRNAs are predominantly expressed in the nervous system and that each LRRTM possesses a specific, partially nonoverlapping expression pattern. The structure and expression profile of LRRTM mRNAs suggest that they may have a role in the development and maintenance of the vertebrate nervous system. All LRRTMs, except LRRTM4, are located in the introns of different alpha-catenin genes, suggesting coevolution of these two gene families.