Susana Raimondi

Chromosomal abnormalities occur commonly in leukemias.
Approximately 90% of lymphoid leukemias and 60% of myeloid leukemias have numerical or structural chromosomal abnormalities. Common structural abnormalities include translocations and deletions. Chromosomal translocations regularly involve genes that regulate different cell-cycle phases including proliferation and senescence.  The abnormal expression of genes involved in the translocations contributes to the clonal expansion process and leukemogenic mechanisms.
There are several evidences that chromosomal abnormalities present in the leukemic clones are formed during embriogenesis. A recent study reveled that 1% of cord-blood samples tested had clones with leukemia-specific abnormalities. Given that only a minority of these children develop leukemia, it is likely that the occurrence of other genetic abnormality contributes to the leukemic transformation or the leukemic clones are naturally eliminated.
Besides contributing to the understanding of the mechanism of disease, chromosomal abnormalities in leukemia carry prognostic implications. For instance, acute lymphoblastic leukemia cases with increased chromosome number (>50 chromosomes) have a good response to conventional leukemia therapy. In the other hand, leukemias with the t(9;22) translocation, or Philadelphia chromosome, present a poor prognosis. In rare occasions, the cytogenetic study may also offer clues for diagnosis that are not revealed by other methods.
Methods for investigating genetic characteristics have progressed dramatically in recent years.  The time-consuming, manual methods of cytogenetic studies are giving place to molecular methods, which are more precise and reproducible.
In this seminar for EduMed, Dr. Susana Raimondi, who has been working at St Jude Children’s Research Hospital for over 20 years and has witnessed the evolution in chromosomes study in leukemias, reviews these methods and its clinical applications.