An 11-Month-Old Male Infant Is Presented with Failure to Thrive

An 11-month-old male infant is presented with failure to thrive and a persistence of anemia. Blood analysis revealed levels of lead to be twice the level deemed toxic. Additional laboratory results reveal high levels of coproporphyrinogen III in the urine. In order to rapidly lower the levels of lead in the child's blood, he is placed on chelation therapy. The child recovers fully following this treatment. The symptoms observed in this child are due to the lead-induced inhibition of which of the following enzymes of heme biosynthesis?

A) d-aminolevulinic acid (ALA) dehydratase
B) d-aminolevulinic acid (ALA) synthase
C) ferrochelatase
D) porphobilinogen (PBG) deaminase
E) uroporphyrinogen decarboxylase