Porphyria is still a very uncommon admission, 1 in every 10,000-20,000. There are only now about 50,000 cases in the country. Just because they were so rare, rumors would spread that if one wanted to see porphyria they could go see them.

Symptoms:
mild anemia
buildup of precursors in heme synthesis
neuropsychiatric symptoms
generalized abdominal pain

If the defect is in an exyme later in the pathway, you get an accumulations of porphyrinogens in the skin. Because of the position of their double bond, they can absorb light light, and spontaneously oxidize. This causes photosensitivity.

So these people would have trouble with sudden light, they will form blisters from the photo damage which would be from reactive oxygen species that would form when these molecules are absorbing light energy.

The liver is also synthesizing heme to a large extent, in cytochromes and particularly P 450 cytochromes that would metabolize various xenobiotics.

The urine would be red in these patients because of the porphyrins that are secreted. Sometimes they would be secreted and it would be colorless but then on standing with oxidation they would turn red.

The dentin in the teeth can also have a red fluoresce.

And all these symptoms are thought to be the basis for the vampire myth at least in Europe.

You can see the symptomology would fit in with a vampire. They would be thin and anemic, out of sight rather out in the sunlight and there might be the mistaken impression, because of the red fluorescence of the teeth, that they were drinking blood. That’s only half serious of course.