Mandibular Prognathism (Progenism)
Pathologic mandibular prognathism is a potentially disfiguring genetic disorder where the lower jaw outgrows the upper, resulting in an extended chin. It is sometimes a result of acromegaly.
This condition is colloquially known as lantern jaw, as well as Habsburg jaw, Habsburg lip or Austrian Lip (see House of Habsburg) due to its prevalence in that bloodline. The trait is easily traceable in portraits of Habsburg family members. This has provided tools for people interested in studying genetics and pedigree analysis. Most instances are considered polygenetic.
It is alleged to have been derived through a female from the princely Polish family of Piasst, its Mazovian branch. The deformation of lips is clearly visible on tomb sculptures of Mazovian Piasts in the St. John’s Cathedral in Warsaw. However this may be, there exists evidence that the trait is longstanding. It is perhaps first observed in Vlad Dracula (1431–1476/77) and Maximilian I (1459–1519).
Traits such as these that were common to royal families are believed to have been passed on and exaggerated over time through royal intermarriage which caused acute inbreeding. Due to the large amount of politically motivated intermarriage among Habsburgs, the dynasty was virtually unparalleled in the degree of its inbreeding. Charles II of Spain is said to have had the most pronounced case of the Habsburg jaw on record. His jaw was so deformed that he was unable to chew.
Many dog breeds have underbite, particularly those with short faces, like shih tzus and boxers. This may be due, as in the case of bulldogs, to a slower growing maxilla in relation to the mandible.