For the computer science term, see Tbox
T-box refers to a group of transcription factors involved in limb and heart development.
In humans and some other animals, defects in the TBX5 gene expression can lead to finger-like thumbs and ventricular septal defects in which there is no separation between the left and right ventricle of the heart and are responsible for Holt-Oram syndrome.
TBX3 is associated with ulnar-mammary syndrome in humans, but is also responsible for the presence or absence of dun color in horses, and has no deleterious effects whether expressed or not.
Genes encoding T-box proteins include: