Inbreeding was not so common in the Bathory family as it was in other Hungarian noble families or in the Hapsburg dynasty, for example. Elizabeth's parents, George and Anna, were not first cousins, as many pretend them to be, but cousins in sixth grade.
However, I suppose there must have been some type of genetical inheritance that made the Bathorys go mad, as there were at least 5 ''insane'' or ''eccentric'' members in each generation!
Elizabeth's father loved tenderly all of his children but, as a warrior under the orders of the Sacred Empire, he was seldom at home, constantly making war against the Turks. Elizabeth's mother, on the other side, was a beautiful and rich woman with a selfish and nasty character. When she had married George, in 1553, she was 22 years old and already twice a widow with four children. It is said that George was the only person that she ever did love and that, for this reason, she was jealous of her own children, as George loved them above all. Of the 8 children Anna bore George, only 4 survived childhood: Stephen, born in 1555; Elizabeth, born in 1560; Sophia, born in 1562; and Clara, born in 1563.
Anna hated Elizabeth with all her heart, as her daughter grew prettier and prettier every year, whilst Anna's beautiful face started to deteriorate. The Bathory's often behaved in the same way: the sons were educated in the arts of the war, while the daughters were educated to negotiate. This was the case of Elizabeth who, aged 9, already read, wrote and spoke perfectly well in Hungarian, German and Latin. With time she would also be quite well in French, English and Spanish and she would learn a bit of Slovakian, Greek, Russian and Danish (I wonder why she learnt Danish??).
When her father died she wasn't yet 10 years old, and her mother, who never loved any of her children, saw her way to get rid of her much hated daughter Elizabeth. So the small Countess was sent to Cachtice, waiting for Count Francis Nadasdy to arrive. I think the mistreatments Anna did to her children had a great influence on them. Elizabeth was the sadistic murderer we all know about, but her older brother, Stephen would commit suicide in 1605, after years of madness and an eccentric behaviour, as he refused to make love with his wife, alleging she was so beautiful she was a Goddess and, because of that, she couldn't be profaned. Her sister Sophia would become mad in 1606 and was ''imprisoned'' in her own rooms until she died two years later. Their younger sister, Clara, was the only one who always lead a normal life and, in 1611, when the trials against Elizabeth were held, Clara forbid her sister's name to be pronounced at her home.