In human, TBX5 mutation causes Holt–Oram syndrome (HOS) which is associaited with upper limb abnormalities (Basson et al., 1997; Bongers et al., 2004), while TBX4 mutation results in small patella syndrome, which is characterized by foot dysplasia (Bongers et al., 2004) (Figure 1C). This evidence concerns the gene TBX5 and Holt-Oram syndrome.