TBX5 and Holt-Oram syndrome: For example, the upper limb muscle defects present in Holt-Oram syndrome (HOS OMIM 142900), a dominant disorder associated with mutations in TBX5 and characterized by upper limb and heart defects (Basson et al., 1997, Li et al., 1997) can be attributed, in part, to disruption of the MCT/ICT (Hasson et al., 2010).