A Novel Variant t(1;22) Translocation - ins(22;1)(q13;p13p31) - in a Child with Acute Megakaryoblastic Leukemia

BACKGROUND The reciprocal translocation t(1;22)(p13;q13) involving the RBM15 and MKL1 genes is an uncommon abnormality that occurs in a subset of acute myeloid leukemia with megakaryocytic differentiation (AMKL). Variant translocations have been infrequently described in this subtype of leukemia. CASE REPORT We describe the case of a 3-month-old girl who presented with progressive abdominal distension, vomiting, and fever. Although there was no morphologic evidence of leukemia in the bone marrow, cytogenetic and metaphase fluorescence in situ hybridization analysis identified an insertion of p13p31 bands of chromosome 1 onto the long arm of chromosome 22, resulting in the karyotype: 46,XX,ins(22;1)(q13;p13p31). Subsequent liver biopsy demonstrated extensive involvement by AMKL. CONCLUSIONS AMKL can present with fewer than 20% blasts in the peripheral blood or bone marrow, necessitating careful evaluation for extramedullary disease. In other situations, bone marrow fibrosis can result in difficult marrow aspirations and a falsely decreased blast count. This case report highlights the critical role of careful cytogenetic and FISH testing in the diagnosis of AMKL.