BAPX1 is the mammalian homolog of the Drosophila bagpipe homeobox gene and is expressed in the splanchnic mesoderm and embryonic skeleton. It is one of the earliest developmental markers for the sclerotome portion of the somite and the gut mesentery. BAPX1 is required for normal skeletal development; homozygous inactivating mutations in the BAPX1 gene result in spodylo-megaepiphyseal-metaphyseal dysplasia (SMMD). It has also been suggested to play a role in the proper development of the mammalian gut and is required for distal stomach development as part of a BARX1-dependent pathway.