Question

Heterozygotes for erythropoietic protoporphyria show only 20 to 30% residualferrochelatase activity rather than the 50% that is normally expected for an autosomal dominant inherited disease. Provide a plausible explanation for this observation.

Short answer

The reason why individuals who are heterozygotes for erythropoietic protoporphyria show only 20 to 30% residual ferrochelatase activity rather than the 50% that is normally expected for an autosomal dominant inherited disease is because of the decreased activity of ferrochelatase that may result in the accumulation of protoporphyrin, since heme production cannot be completed.

Step-by-step solution

Erythropoietic protoporphyria and Ferrochelatase

Erythropoietic protoporphyria is a type of porphyria, a syndrome that occurs when protoporphyrin accumulated in the plasma and red blood cells.

Ferrochelatase is the enzyme that is involved in heme biosynthesis. It inserts Fe(II) into protoporphyrin IX as a last step of the synthesis process.

Reason why heterozygotes for erythropoietic protoporphyria show only 20 to 30%

Decreased activity of ferrochelatase may result in the accumulation of protoporphyrin, since heme production cannot be completed.

That is why individuals who are heterozygotes for erythropoietic protoporphyria show only 20 to 30% residual ferrochelatase activity rather than the 50% that is normally expected for an autosomal dominant inherited disease.