Clinical Pathology: General Principles, Hematology & Coagulation, Immunology & Histocompatibility, Urinalysis, Body Fluids, Clinical Microscopy, Genetic Testing

• Transient abnormal myelopoiesis (TAM) occurs in approximately 10% of newborns with trisomy 21.

• There is an abnormal proliferation of myeloid precursors, typically megakaryocytes. CD61 immunohistochemistry can be useful is assigning the megakaryocytic lineage to such cells in tissue sections.

• TAM will typically resolve spontaneously within the first few months of life. Organomegaly and liver disease occur in a significant proportion of these patients and can be fatal. Only in such a circumstance would aggressive chemotherapy be warranted. Other patients can be completely asymptomatic.

• There is a substantial risk (20% to 30%) for the development of nontransient acute leukemia within the first 3 years of life in patients with TAM. The preleukemic phase can be associated with dysplasia and features of refractory cytopenia of childhood.

• The prognosis of acute myeloid leukemia (AML) in this setting (typically associated with GATA-1 mutation) is better than in cytogenetically normal children.

• Other clinical features include thrombocytopenia, vesicular skin disease, marrow fibrosis (teardrop cells), and if in utero, hydrops fetalis.

• Patients with trisomy 21 have an increased incidence of all types of leukemia in all age groups.