The culmination of this was Charles II (1661-1700), the most inbred individual of all. Like others in his ancestry, he had a long, cadaverous face and a lower jaw that jutted out so far that his teeth didn't meet. The technical term for this was Mandibular Prognathism, or Habsburg jaw. His tongue was so enlarged that speaking and swallowing were difficult. He also had epilepsy and was apparently unable to reproduce. His family seemed more concerned about keeping him alive than educating him, so he could barely read and write. he may have been mentally slow. In any event, "much of his reign consisted of consisted of others ruling the country in his stead."
http://historycollection.com/40-facts-about-the-inbred-king-charles-ii-spain/ It is speculated that he had two additional genetic disorders: pituitary hormone deficiency and distal renal tubular acidosis, recessive traits that would have been expressed because of inbreeding. The former condition may have interfered with normal growth. The latter results in too much acid in the blood. Together, they left Charles with weak muscles, a large head, and digestive problems.
His autopsy revealed some grim facts about his health: " “a very small heart, lungs corroded, intestines putrefactive and gangrenous, three large stones in the [!] kidney, a single testicle black as coal, and his head full of water.”
It was not unusual for royals to marry blood relatives in those days, but the Spanish Habsburgs carried this farther than most: in the dynasty's 200 years, 9 of 11 marriages were between cousins of various degrees, or uncle/niece matchups. Likewise for Charles, whose
father was the uncle of his mother.
Roman Vilas, a genetics professor at the University of Santiago de Compostela, asked a team of maxillofacial surgeons to analyze 66 portraits of 15 members of the Spanish Habsburgs. They looked for 11 features that defined excessive development of the lower jaw, and seven features that defined underdevelopment of the upper jaw. The more inbreeding was present, the greater was the amount of jaw deformity. The technical term for this is homozygosity, or increased concentration of the same genes.
Whether Charles's other health problems were related to his jaw deformity is hard to say.
Perhaps he was lucky not to have had other well-known genetic disorders such as haemophilia or porphyry.
But there is scant comfort to be found in the absence of these disorders. As it was, life for him was touch and go for the 38 years that he survived.