Myeloid Leukemia of Down Syndrome

Simple Summary Patients with Down Syndrome have been thoroughly studied over the past 100 years, and many attempts have been made to attain insight into the developmental biology of DS. Given the association of DS with several hematological disorders, it was more than appealing to us to conduct a literature research to identify the rare subtype of acute myeloid leukemias associated with DS -Myeloid Leukemia of Down Syndrome- to investigate its occurrence, clinical presentation, and typical characteristics in terms of blast morphology and immunophenotype, and suggest optimal criteria for early diagnosis and progression monitoring. Among others, the multistep clonal evolution process is being analyzed here, while challenges on treatment of those patients are presented in detail. We suggested that a standardized holistic approach of care for children with Myeloid Leukemia of Down Syndrome should be ensured and applied to provide more enhanced outcomes to those patients. Myeloid leukemia of Down syndrome (ML-DS) is characterized by a distinct natural history and is classified by the World Health Organization (WHO) as an independent entity, occurring with unique clinical and molecular features. The presence of a long preleukemic, myelodysplastic phase, called transient abnormal myelopoiesis (TAM), precedes the initiation of ML-DS and is defined by unusual chromosomal findings. Individuals with constitutional trisomy 21 have a profound dosage imbalance in the hematopoiesis-governing genes located on chromosome 21 and thus are subject to impaired fetal as well as to neonatal erythro-megakaryopoiesis. Almost all neonates with DS develop quantitative and morphological hematological abnormalities, yet still only 5-10% of them present with one of the preleukemic or leukemic conditions of DS. The acquired mutations in the key hematopoietic transcription factor gene GATA1, found solely in cells trisomic for chromosome 21, are considered to be the essential step for the selective growth advantage of leukemic cells. While the majority of cases of TAM remain clinically 'silent' or undergo spontaneous remission, the remaining 20% to 30% of them progress into ML-DS until the age of 4 years. The hypersensitivity of ML-DS blasts to chemotherapeutic agents, including but not limited to cytarabine, and drugs' increased infectious and cardiac toxicity have necessitated the development of risk-adapted treatment protocols for children with ML-DS. Recent advances in cytogenetics and specific molecular mechanisms involved in the evolution of TAM and ML-DS are reviewed here, as well as their integration in the improvement of risk stratification and targeted management of ML-DS.