Laughing Madness

Severe mental instability, and less regard for personal wellbeing. Doesn't outright kill, though contracting this disease drastically reduces one's life expectancy due to increased risk taking.  

Carriers

Interesting about this disease is that all Midland nobles are actually dormant carriers and genetically immune to the disease. In times long past, the disease was simply seen as another consequence of power.   This is why commoners who kill and eat nobles tend to go insane (or, well, more insane than you'd have to be to kill and eat a guy). Note that having a fireblooded father can confer the genetic immunity (or more typically, partial resistance) to this disease, while not actually granting any affinity for Fire- this is why cases exist where the commoner cannibals aren't driven mad.