>>320267
For those who may not know, that condition is called porphyria and it's considered one of the most likely candidates for the origin of vampire myths. It's basically a chicken-or-egg situation, since porphyria is pretty much just a disorder that causes your skin to burn in contact with sunlight. It also makes your piss turn purple/red and is (thought to be) caused (or become more severe) by prolonged inbreeding. IIRC it is also linked with a propensity to mental illnesses, but that could just be another effect of the common cause(s) rather than an actual effect caused by porphyria.