We report a case of a 2-year-old boy with Noonan syndrome (NS) complicated by an abnormality of chromosome 7 after treatment of acute lymphoblastic leukemia (ALL) . The boy was admitted to our hospital with fever and gingival bleeding. Laboratory findings showed anemia and thrombocytopenia. Bone marrow findings were proliferation of abnormal lymphoblastoid cells (FAB L1) , and surface markers were positive for CD10, CD19, and HLA-DR. Both bone marrow and peripheral blood karyotypes were 46 ,XY.

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... He also had typical phenotypes of NS, including multiple congenital heart disease (atrial septal defect , hypertrophic obstructive cardiomyopathy, and peripheral pulmonary stenosis), hyperterolism, thoracic malformation , left testicular agenesis, and mild mental retardation. He was diagnosed as ALL and was treated with chemotherapy . He entered complete remission (CR), which is currently maintained. But chromosomal analysis of bone marrow during maintenance chemotherapy showed abnormal karyotype, 46,XY,add(7)(q11). The morphological findings of this marrow showed dyplasia of myeloid cells. It was suspected that he also had myelodysplastic syndrome (MDS). Although it is unclear whether his MDS was related to chemotherapy or NS , recently some reports have shown an association between MDS and NS . Further studies are required to examine the cytogenetic background in hematological disorders associated with Noonan syndrome .