Hereditary coproporphyria is a rare type of porphyria that can have acute (severe but usually not long-lasting) symptoms along with symptoms that affect the skin. The disorder results from low levels of the enzyme responsible for the sixth step in heme production. Heme is a vital molecule for all of the body's organs. It is a component of hemoglobin, the molecule that carries oxygen in the blood. Hereditary coproporphyria is a subtype of porphyria. The signs and symptoms of hereditary coproporphyria are similar to those of acute intermittent porphyria, but attacks of acute symptoms tend to be less severe. Acute attacks usually begin in adulthood and cause abdominal pain, vomiting, diarrhea, and constipation. During an attack, a person may also experience muscle weakness, seizures, and mental changes such as anxiety and hallucinations. These signs and symptoms are triggered by nongenetic factors such as certain drugs, alcohol, dieting or fasting, and certain hormones. In about 30 percent of people with hereditary coproporphyria, the skin is overly sensitive to sunlight. Exposed areas become fragile and develop blistering and scarring. Skin symptoms may be milder between acute attacks. A rare form of this disorder called harderoporphyria has severe signs and symptoms that begin in infancy or childhood. In addition to the health problems listed above, children with harderoporphyria experience yellowing of the skin and the whites of the eyes (jaundice) and a low number of red blood cells (anemia).