My Top 5 Family Issues that leads to Serial Killing (in Movies)

According to the movies; if there's an affair, an accidental death or having a Celtic background in your family, chances are there's a series killer in your clan.
I'll give examples:

Scream series - The reason behind this madness started with mother abandoning her son


Friday the 13th - Death of a son led mother to murder


Halloween - A insane brother with a curse


Prom Night - A sister's death drove a brother to massacre


Sleepaway Camp - A sister's death causes a brother to become the sister and kill