T-box transcription factor TBX3 is a protein that in humans is encoded by the TBX3 gene.This gene is a member of a phylogenetically conserved family of genes that share a common DNA-binding domain, the T-box. T-box genes encode transcription factors involved in the regulation of developmental processes. Defects in TBX3 are the cause of ulnar-mammary syndrome (UMS). UMS is characterized by ulnar ray defects, obesity, hypogenitalism, delayed puberty, hypoplasia of nipples and apocrine glands