Lizzie Borden took an axe
Gave her mother forty whacks
When she saw what she had done
She gave her pappy forty-one.
Axe murderers do seem to run in families at times, some sort of heritable psychological defect I suppose. It can also be bred out. I have two in my lines, way back, seventeenth century. A few in the eighteenth century could have been characterized as prone to manias, but it led to accomplishments that were fairly impressive for that time and place, rather than blunt head trauma for some unfortunate individual.
These two were unrelated, though they look like bookends. Acting out the same, looking the same, they were closer than we know, and the crazy might run pretty deep. There may be another reason for killing the great grandmother of the one as a result. Maybe she disapproved of something.