**Core Concept**
Sideroblastic anemia is a disorder characterized by the accumulation of iron in mitochondria of erythroblast cells, leading to the formation of sideroblasts. This type of anemia is caused by defects in the heme biosynthetic pathway, resulting in the accumulation of iron within cells.

**Why the Correct Answer is Right**
Chronic poisoning with isoniazid, a medication used to treat tuberculosis, can lead to sideroblastic anemia. Isoniazid inhibits the enzyme alanine aminotransferase, which is necessary for the conversion of succinyl-CoA to α-ketoglutarate in the heme biosynthetic pathway. This inhibition disrupts the normal flow of electrons and results in the accumulation of iron within cells. Additionally, isoniazid can also interfere with the activity of other enzymes involved in the heme biosynthesis pathway, further contributing to the development of sideroblastic anemia.

**Why Each Wrong Option is Incorrect**
* **Option A:** Lead poisoning primarily causes microcytic anemia, not sideroblastic anemia, due to its effect on heme synthesis and the inhibition of δ-aminolevulinic acid dehydratase.
* **Option B:** Chronic arsenic poisoning can cause various types of anemia, including microcytic and normocytic anemia, but it is not typically associated with sideroblastic anemia.
* **Option C:** Chronic poisoning with mercury is more likely to cause kidney damage and neurological symptoms than anemia.

**Clinical Pearl / High-Yield Fact**
It is essential to recognize that sideroblastic anemia can be caused by a variety of factors, including genetic mutations, certain medications (such as isoniazid), and exposure to heavy metals. A thorough medical and occupational history is crucial in identifying the underlying cause of this disorder.

**Correct Answer: C. Lead poisoning primarily causes microcytic anemia, not sideroblastic anemia, due to its effect on heme synthesis and the inhibition of δ-aminolevulinic acid dehydratase.