Isolated deletion of which chromosome causes myelodysplastic syndrome –

**Core Concept**
Myelodysplastic syndrome (MDS) is a group of disorders caused by poorly formed or dysfunctional blood cells, often due to genetic abnormalities. Isolated deletion of a specific chromosome is a common cause of MDS, leading to disruption of normal hematopoiesis.

**Why the Correct Answer is Right**
The isolated deletion of chromosome 5q is a common genetic abnormality associated with MDS, specifically with the 5q- syndrome. This deletion leads to the loss of the EGR1 gene, which encodes a transcription factor involved in the regulation of cell growth and differentiation. The loss of this gene contributes to the development of MDS by impairing normal hematopoiesis. Other genetic abnormalities, such as deletions or mutations in other chromosomes, can also contribute to the development of MDS, but 5q deletion is a specific and well-defined cause.

**Why Each Wrong Option is Incorrect**
**Option A:** Deletion of chromosome 7q is associated with myeloproliferative neoplasms, such as chronic myeloid leukemia, but is not a primary cause of myelodysplastic syndrome.

**Option B:** Deletion of chromosome 20q is not a well-defined or commonly recognized cause of myelodysplastic syndrome.

**Option C:** Deletion of chromosome 17p is associated with acute myeloid leukemia and other myeloid malignancies, but is not a primary cause of myelodysplastic syndrome.

**Clinical Pearl / High-Yield Fact**
The 5q- syndrome is characterized by a distinct clinical and morphological profile, including isolated del(5q), normal platelet count, and a relatively favorable prognosis compared to other forms of MDS.

**Correct Answer:** B.