Most porphyrias are inherited. However, one type, Porphyria Cutanea Tarda (PCT), may either be inherited (also referred to as “familial”) or “sporadic” due to various environmental factors. In each type of porphyria there is a deficiency of a specific enzyme. These enzymes are involved in the synthesis of heme, a substance important to many body functions which is found in large amounts in bone marrow and red blood cells (which contain hemoglobin), and which also has important functions in the liver, muscles, and other tissues. The type of porphyria present is determined by which enzyme is deficient; these enzyme deficiencies are usually inherited. Environmental factors, such as drugs, diet, and sun exposure can, depending on the type of porphyria, greatly influence the severity of symptoms.
Sun sensitivity is the main symptom in CEP, EPP, XLP and PCT. VP and HCP, which are acute porphyrias, can also have blistering sun sensitivity. The degree of sensitivity to sunlight varies considerably. Patients with sun sensitivity have high levels of porphyrins in the blood plasma which, depending on the type of porphyria, have originated from the liver or the bone marrow. Ultraviolet light interacts with porphyrins in such a way as to damage skin tissue. In general, for patients with CEP, EPP, XLP and PCT they should protect themselves from sun exposure. For patients with VP and HCP, only if they have sun sensitivity do, they need to protect themselves from sun exposure.
Individuals with a disease-causing mutation without symptoms have "latent" acute porphyria. However, this does not mean that such an individual will never have symptoms. Genetic factors (that is, the presence of a porphyria-causing gene mutation) are not the only factors involved. Exposure to certain environmental factors, such as medications can, greatly influence whether an individual with a mutation in a porphyria-causing gene has symptoms This is why it is important that all family members of individuals diagnosed with acute porphyria be tested whether they have symptoms or not, and that all individuals who have a confirmed diagnosis of acute porphyria be educated about and follow the recommended precautionary and preventive measures.