Abstract

Background
Pentasomy involving duplication of isochromosome 21;der(21;21)(q10;q10) is a rare cytogenetic abnormality linked primarily to acute lymphoblastic leukemia (ALL) and less frequently to acute myeloid leukemia (AML) or myelodysplastic syndromes (MDS). These abnormalities often occur in complex karyotypes and might co-occur with t(12;21).
Case Presentation
A unique case of ALL was reported in a 14-year-old male presented with pentasomy 21 from duplicated der(21;21)(q10;q10) along with deletion 13q as primary abnormalities. Bone marrow and flow cytometry showed 90% B-lymphoid blast cells. Chromosome analysis and Fluorescence in situ hybridization (FISH) revealed interstitial deletion 13q and der(21;21)(q10;q10) duplication, resulting in five RUNX1 gene signals. While duplicated isochromosome/isodicentric chromosome 21 was documented in isolated cases of ALL and AML, this was the first report of this abnormality co-existing with deletion 13q in the present case of ALL, suggesting a unique contribution to disease pathogenesis. The amplification of 21q genes, including RUNX1, ETS, and ERG, might influence pathogenesis and warrants further investigation.
Conclusion
The co-occurrence of Pentasomy 21 and 13q deletions represented a novel finding, prompting investigations into their combined impact on clinical outcomes. This unique cytogenetic combination highlighted the need for further studies to understand its impact on ALL pathophysiology.

Key words: Derivative (21;21)(q10;q10), Fluorescence in situ hybridization, FISH, Karyotype, Pentasomy 21, 13q deletion, Acute lymphoblastic leukemia, Case report.