Holt–Oram syndrome is an autosomal dominant disorder that affects bones in the arms and hands (the upper limbs) and may also cause heart problems. The syndrome includes an absent radial bone in the arms, an atrial septal defect, and a first degree heart block. Holt–Oram syndrome is considered to be a phenocopy of thalidomide, since both the genetic disorder and the teratogenic effects have similar presentations in individuals.