The leucine-rich (LRR) repeat is a 20-30 amino acid motif that forms a hydrophobic Alpha/Beta horseshoe fold, allowing it to accommodate several leucine residues within a tightly packed core. All LRR repeats contain a variable segment and a highly conserved segment, the latter of which accounts for 11 or 12 residues of the entire LRR motif. The LRRTM protein family plays a role in the regulation of various cellular events during nervous system development. Localizing predominantly to the nervous system, LRRTM family members are known to exhibit synaptogenic activity. LRRTM3 (leucine rich repeat transmembrane neuronal 3) is a 581 amino acid single-pass type I membrane protein belonging to the LRRTM family. LRRTM3 is involved in the development and maintenance of the vertebrate nervous system, and contains ten LRR repeats. Expressed in neuronal tissues, LRRTM3 is encoded by a gene that maps to a region of chromosome 10 that has been linked to late-onset Alzheimer disease and elevated plasma Beta-Amyloid. As a result of alternative splicing events, two LRRTM3 isoforms exist.