7. Diprosopus
The condition is also known as craniofacial duplication and is extremely rare. It affects humans and animals alike. Facial features of persons with diprosopus are partially duplicated, while the rest of the body is unaltered. Researchers have proposed several explanations as to why the condition is developed. One of the explanations is that the protein SHH, which is crucial for craniofacial patterning during the stages of development, is altered.