This may sound a troll question, but hear me out - when we think of royal inbreeding, the Habsburgs first come in mind where first cousins or uncles and aunts had children with their nieces or nephews. Another good example should be the Zoroastrian rulers of the Sassanid empire , where often in an attempt to keep the bloodline pure,brothers entered into sacred matrimony with their sisters. Their offsprings had legitimate genetic health issues, Carlos II of Spain being a prime example. Despite all of this, there are little to no historical records of Ptolemaic monarchs having legitimate health issues, coming from the inbreeding of close relatives - Ptolemy V for example was a child of Ptolemy IV and Arsinoe III,both of which were brother and sister, Ptolemy X who was the child of Ptolemy VII and Cleopatra III ( again - siblings ), and even Cleopatra VII, the lover of Caesar and wife of Mark Anthony ,was the offspring of siblings. So why is it that most of them weren't disfigured, had a distinct chin and problems walking, talking or even reproducing, like others?