Abstract
The only cytogenetic alteration defining a subtype of a myelodysplastic syndrome is represented by the deletion of the long arm of chromosome 5 (del(5q)), now classified as MDS with isolated del(5q). This subtype is associated with a peculiar phenotype mainly dependent on the haploinsufficiency of several genes located on the deleted arm of chromosome 5. These patients show a good prognosis and respond to treatment with lenalidomide, but some cases progress to acute myeloid leukemia. Molecular studies have, in part, elucidated the heterogeneity of MDS with isolated del(5q), mainly related to the association with different co-mutations that may affect leukemic transformation and survival. In other MDS patients, del(5q) is combined with other chromosomal abnormalities, giving rise to a condition of complex karyotype, associated with frequent TP53 mutations and with a poor prognosis. Two different molecular pathways seem to be responsible for the generation of MDS with isolated del(5q) or of MDS with del(5q) associated with a complex karyotype.