Prognathism (also known as Habsburg Jaw) is a term used to describe the positional relationship of the mandible and/ormaxilla to the skeletal base where either of the jaws protrudes beyond a predetermined imaginary line in the coronal plane of the skull. Prognathism is well recorded as a trait of several historical individuals. The most famous case is that of the House of Habsburg, among whom mandibular prognathism was a family trait; indeed, the condition is frequently called “Habsburg Jaw” as a result of its centuries-long association with the family. Among the Habsburgs, the most prominent case of mandibular prognathism is that of Charles II of Spain, who had prognathism so pronounced he could neither speak clearly nor chew as a result of generations of politically motivated inbreeding.
The Habsburgs sought to consolidate their power by the frequent use ofconsanguineous marriages, with ultimately disastrous results for their gene pool. Marriages between first cousins, or between uncle and niece, were commonplace in the family. A study of 3,000 family members over 16 generations by the University of Santiago de Compostela suggests that inbreeding directly led to their extinction. The gene pool eventually became so small that the last of the Spanish line Charles II, who was severely disabled by genetic disorders, possessed a genome comparable to that of a child born to a brother and sister, as did his father, likely due to “remoteinbreeding”. The consequence of this and other genetic defects was the War of the Spanish Succession.
Image 1: Charles II of Spain.
Image 2: Felipe IV of Spain.
Image 3: Charles V, Holy Roman Emperor.