Neuronatin(Nnat) is a recently cloned brain-specific gene that is selectively expressed during brain development. Human Nnat gene spans 3 973 bases and contains three exons and two introns. Nnat mRNA has two different splice isoforms, α and β, the former encoding a protein of 81 amino acids and the latter 54 amino acids. These two isoforms share the same open reading frame, but the α-form contained an additional 81 bp sequence inserted in the middle of the coding region. The human Nnat is a single copy gene located at chromosome 20q11.2～12, while the rat gene is located on the distal region of chromosome 2, 2H1. Nnat is an imprinted gene and expressed from the paternal allele, while the maternal allele is methylated and silenced. As Nnat is highly expressed in the central nervous system from mid-gestation through early postnatal development and down-regulated in adulthood and senescence, Nnat may be involved in brain development and differentiation. The expression is also detected in the adult brain stem, suggesting roles in neuroplasticity. The deduced protein sequence contains a hydrophobic N-terminal and a hydrophilic C-terminal, and appears to code for a transmembrane protein. The biological function of Nnat remains to be elucidated.