TB, Xenopus/Amphibian,5 (T-bo, Xenopus/Amphibian, 5) is a transcription factor. It is a member of a phylogenetically conserved family of genes that share a common DNA-binding domain, the T-bo, Xenopus/Amphibian,. T-bo, Xenopus/Amphibian, genes encode transcription factors involved in the regulation of developmental processes. It is closely linked to related family member T-bo, Xenopus/Amphibian, 3 (ulnar mammary syndrome) on human chromosome 12. The TB, Xenopus/Amphibian,5 protein may play a role in heart development and specification of limb identity. Mutations in this gene have been associated with Holt-Oram syndrome, a developmental disorder affecting the heart and upper limbs.