5q Deletion/Monosomy (MDS)This refers to the 5q- syndrome, a specific subtype of Myelodysplastic Syndrome (MDS), which is a clonal hematopoietic stem cell disorder.

Genetic Abnormality: Characterized by a deletion of part of the long arm (q-arm)3 of chromosome 5, typically del(5q), as the sole cytogenetic abnormality or with one other abnormality.
Complete loss (monosomy 5) is less common and generally carries a poorer prognosis.
Pathogenesis: The disease results from the haploinsufficiency (loss of one copy) of multiple genes in the deleted region, particularly the Commonly Deleted Region (CDR).
Loss of the RPS14 gene is thought to lead to macrocytic anemia and activation of the p53 tumor suppressor pathway in erythroid precursors.
Loss of microRNAs (e.g., miR-145, miR-146a) contributes to megakaryocyte abnormalities and normal/high platelet counts.

Clinical Features:
Macrocytic Anemia: Often severe and transfusion-dependent.
Platelet Count: Usually normal or elevated (thrombocytosis), which is distinct from many other forms of MDS.
Bone Marrow: Typically hypercellular with erythroid hypoplasia (reduced red cell precursors) and characteristic abnormal megakaryocytes that are numerous, small, and have hypolobated (non-lobulated) nuclei
Prognosis and Treatment: Considered a relatively low-risk form of MDS compared to those with complex karyotypes.
It has a low rate of progression to Acute Myeloid Leukemia (AML).
The drug Lenalidomide is highly effective for this subtype, often leading to transfusion independence by targeting the 5q deleted cells.