The relationship between precursors in the heme synthesis pathway and the type of porphyria resulting from excess buildup is:

The relationship between precursors in the heme synthesis pathway and the type of porphyria resulting from excess buildup is:

• A. Excess of early precursors causes neurologic porphyrias and excess of late precursors causes cutaneous porphyrias.
• B. Excess of early precursors causes cutaneous porphyrias and excess of late precursors causes neurologic porphyrias.
• C. Excess of early precursors causes both neurologic and cutaneous porphyrias, whereas excess of late precursors causes only cutaneous porphyrias.
• D. Excess of early precursors causes both neurologic and cutaneous porphyrias whereas excess of late precursors causes only neurologic porphyrias.

Answer: (A)

In heme biosynthesis, where the block occurs determines which intermediates build up and what symptoms appear. Early intermediates (such as delta-aminolevulinic acid and porphobilinogen) accumulating due to a defect cause neurologic, often neurovisceral, porphyrias. Late intermediates (porphyrinogens and porphyrins) build up in other blocks and are photoreactive, leading to cutaneous porphyrias with photosensitivity. So excess early precursors are linked to neurologic symptoms, while excess late precursors are linked to skin-related, cutaneous symptoms.

In heme biosynthesis, where the block occurs determines which intermediates build up and what symptoms appear. Early intermediates (such as delta-aminolevulinic acid and porphobilinogen) accumulating due to a defect cause neurologic, often neurovisceral, porphyrias. Late intermediates (porphyrinogens and porphyrins) build up in other blocks and are photoreactive, leading to cutaneous porphyrias with photosensitivity. So excess early precursors are linked to neurologic symptoms, while excess late precursors are linked to skin-related, cutaneous symptoms.