The Habsburg jaw is a prominent lower jaw and lips that was common in the Habsburg dynasty. It's a genetic disorder caused by inbreeding, or consanguineous marriage, that was used by royal families to maintain their bloodlines. 

Causes 

•Inbreeding
The Habsburgs rarely married outside the dynasty, which led to generations of inbreeding.



•Consanguineous marriage
The Habsburgs married close relatives, such as first cousins or uncles with nieces.



Symptoms 

•A pronounced lower jawline
•A recessed upper jaw
•A jutting chin
•A thick, everted lower lip
•A large, often misshapen nose
•Flat malar areas
•Mildly everted lower eyelids
Effects 

•The condition could be so pronounced that it prevented some members of the dynasty from eating or speaking properly.