Excess porphyrins tend to accumulate in which organ systems?

• A. Liver and bone marrow
• B. Brain and spinal cord
• C. Kidney and pancreas
• D. Muscle and fat

Answer: (A)

Porphyrin accumulation reflects where heme synthesis happens most actively. The heme biosynthetic pathway operates primarily in the liver and in the erythroid precursors of the bone marrow. When an enzymatic step is defective, the intermediates build up in these tissues. Therefore, excess porphyrins tend to accumulate in the liver and bone marrow. In hepatic porphyrias the excess porphyrins mainly involve the liver; in erythropoietic porphyrias they accumulate in the bone marrow and red blood cells. Other organs like brain, kidneys, pancreas, muscle, or fat aren’t the main sites of porphyrin buildup, though some symptoms can arise from circulating precursors.