USMLE Why don't all porphyrias cause microcytic anemia?

[lucky01]

if lead poisoning can cause microcytic anemia due to defective heme synthesis, why don't the other porphyrias cause microcytic anemias since they cause a defective heme synthesis too?

sorry if this question seems silly, just trying to grasp a better understanding of this logically.

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[Jabbed]

if lead poisoning can cause microcytic anemia due to defective heme synthesis, why don't the other porphyrias cause microcytic anemias since they cause a defective heme synthesis too?

sorry if this question seems silly, just trying to grasp a better understanding of this logically.

The enzyme deficiency does not produce a complete block of heme synthesis (you would expect a microcytic sideroblastic anemia in that case). The clinical manifestations are usually due to accumulation of intermediate substrate rather than deficiency of product.

(This question bugged me for months and I finally got an answer from a heme-onc the other day)

 

[lucky01]

The enzyme deficiency does not produce a complete block of heme synthesis (you would expect a microcytic sideroblastic anemia in that case). The clinical manifestations are usually due to accumulation of intermediate substrate rather than deficiency of product.

(This question bugged me for months and I finally got an answer from a heme-onc the other day)

Ah! You saved me months of being bugged. Thank you!!