Henry VIII achieved enduring fame (and portrayal by a series of skinnier and skinnier actors) by lopping off heads left, right, and center. Well, technically only left and right, since he ordered the execution of just two of his wives. Another two he disposed of legally, but less violently, through divorce and annulment. Henry's motivation for killing fully one third of his wives and divorcing another third was his desire for a son. Although many wives got pregnant by him, a series of miscarriages and stillborn children, as well as a few unlucky baby girls, left him without a male heir for a long time. Bad luck happens, certainly, but some think there was a biological reason why Henry took so long to get the male child he was trying for.
Some people think that blood group was a reason why so many of Henry's wives suffered so many miscarriages. The presence of the rh antigen is noted as positive - as in "My blood type is O positive." The abscense of it is denoted as negative: "My blood type is AB negative." If a woman is rh negative and is pregnant by a man who is rh positive, her body could react to the fetus as it would a virus or other foreign body. Now there are shots that are given that can desensitize this immune response. Not so back in Henry's day. The blood group argument is strong, but it relies on the unsubstantiated idea that Henry married a lot of rh negative women. About 80-85% of Caucasians are rh positive, so Henry would have had very bad luck - as would his wives, of course.
Another theory is that Henry had the Kell antigen. The Kell antigen works much the same way rh types do. If the pregnancy is Kell positive, the woman's body can attack the fetus and end the pregnancy. What's more, the men carrying the Kell antigen tend to develop McLeod's syndrome in later life. McLeod's syndrome is characterized by degenerating motor function, muscle spasms, hyperactivity, and mental and emotional instability. It generally sets in between ages 30 and 40, and may explain why Henry VIII, who by everyone's account was a good-natured and athletic young man, became sedentary, paranoid, and some would say psychotic in later life.
Many disagree that some genetic problem was the source of all the drama. King Henry VIII had many confirmed medical problems, such as syphilis that could lead to mental and physical instability. They also point out that Henry's first wife, Katherine, delivered a healthy child after her fifth pregnancy. Usually the Kell antigen results in a healthy first pregnancy and frequent miscarriages after that. Supporters of the theory disagree, arguing that if the fifth child, Mary, inherited the Kell recessive gene from her father, the pregnancy would be in no danger. They also point out that Henry caused 11 to 13 known pregnancies, and only four produced a healthy infant. Although childbirth itself was risky, that kind of miscarriage rate was unusual even for the time. It would be especially unusual for a woman who carried the child of a king, considering she wouldn't suffer from over-work or malnutrition.
Barring a shovel, a strong stomach, some luck, and a great deal of genetic testing, there's no way to know if Henry was the genetic cause of all of his own problems. Although Henry's behavior was bad, it earned him an enduring place in history and pop culture. That has to be worth something - although not, I suspect, to his wives.