T-box transcription factors are a group of phylogenetically conserved genes that contain a uniquely defining DNA-binding domain, the T-box domain. These genes are believed to be involved in the regulation of development processes. In mouse embryo development, Tbx15 is expressed at the beginning of day 9.5, primarily in the craniofacial region and in the developing limbs. Twelve human T-box genes have been isolated so far. TBX 18 has been reported to be involved in numerous development processes and to act as an antiapoptotic factor.