two transcripts (splice variants) and RNA transcripts detected by RNA-Seq screens have been observed in brain tissues, striated muscle, white blood cells (granulocytes, monocytes), and esophageal mucosa. Yet, definitive evidence for human BPIFB9 protein has never been produced and is unlikely to happen. The non-human version of this protein, however, is well known. Vomeromodulin is highly expressed in nasal mucosa, particularly within a structure known as the Vomeronasal organ. The vomeronasal organ is present and well-developed in many mammals to process pheromone odors into neural signals to the brain, but the chemical and neural components of the vomeronasal system have been completely inactivated in most primates, including humans. In this context, BPIFB9-type proteins are thought to be similar to odorant binding proteins which presents odorant molecules to chemical odorant receptor molecules. Those odorant receptors, in turn, are associated with nasal epithelial cells integrated with olfactory neurons that project back to the brain's oflactory areas and hypothalamus. It has been established that the genes and proteins for these components are present and active in many mammal species, but in higher primates the genes are found to be mutated and appear as non-functional pseudogenes, like BPIFB9P. References External links Pseudogenes Genes on human chromosome 20