Selective involvement of cells carrying extra chromosomes 21 in a child with acute non-lymphocytic leukaemia

Trisomy 21 in Acute Promyelocytic Leukemia

We present a case of a 64-year-old male, diagnosed to have acute promyelocytic leukemia with trisomy 21. He came to the hospital with bleeding secondary to disseminated intravascular coagulation. Promyelocytes in the blood and bone marrow contained abundant, prominent azurophilic granules. Cytogenetic studies revealed trisomy 21. The karyotypic abnormality reverted back to normal 46,XY, pattern after chemotherapy. The typical morphologic and cytogenetic features of acute promyelocytic leukemia are briefly discussed.

Acute lymphoblastic leukemia with trisomy 21 constitutional mosaicism

Acute lymphoblastic leukemia was diagnosed in an 11-year-old girl with mild signs of Down's syndrome. She was known since birth to have a constitutional mosaicism (46,XX/47,XX,+21c). At initial diagnosis of acute leukemia, additional chromosome changes were found in bone marrow blasts: hyperdiploidy > 50, with a structural abnormality. She was treated with a standard chemotherapeutic protocol, and has remained in complete remission for more than 3 years. The constitutional mosaicism evolved toward normalization year after year in the blood and under the effect of chemotherapy in the bone marrow.

Hematological changes in Down's syndrome

The many hematological abnormalities observed in patients with Down's syndrome have intrigued hematologists for many years. This review summarizes recent studies concerning the hematological findings in newborn infants with Down's syndrome, the transient leukemoid/leukemia-like proliferative disorders in these infants, the increased incidence of leukemia and types of leukemia in patients with Down's syndrome, and immunological studies of these patients. In addition, studies concerning the significance of the extra genetic material in chromosome 21 found in patients with Down's syndrome are discussed. It appears that the extra genetic material in chromosome 21 confers a proliferative advantage to hematopoietic stem cells, and may make them more prone to further karyotypic changes leading to leukemia. Megakaryocytic proliferative disorders are more common in patients with Down's syndrome. The spectrum of myeloproliferative disorders including myelofibrosis, myeloid metaplasia, and megakaryoblastic leukemia is seen in these patients. Studies of the genetic loci on chromosome 21 have demonstrated loci for enzymes involved in purine biosyntheses. Further studies of specific loci on chromosome 21 may help explain the hematopoietic growth advantages found in the stem cells with an extra chromosome 21.