T-box genes encode a family of transcription factors that have been identified in all metazoans and which play diverse roles during embryonic development. TBX5, a member of T-box family, has an essential role in the initiation of limb outgrowth and heart development. Genetic variation near TBX5 that associates with PR and/or QRS interval variation, which suggests that TBX5 plays a role in CCS function in the general population. Because 77 % amino acid sequence of TBX5 is identical to TBX4, this antibody recognizes both TBX4 and TBX5.