[Juvenile type of chronic myelogenous leukemia in a 3 6/12 year old boy with trisomy 21 mosaicism but no symptoms of Down's syndrome (author's transl)].

In a 3 6/12 year old boy, with the juvenile type of chronic myelogeneous leukemia cytogenetic examination of bone marrow and blood, performed two months before onset of the acute blastic crisis, showed two cell lines: the first one with a normal karyotype 46, XY and the second one with a trisomic karyotype 47, XY, +21. This finding of a mosaic trisomy 21 in a patient without symptoms of Down's syndrome allow to assume the trisomy cells to be malignant, and the type of mosaicism to be proliferative. This karyologic finding could be taken for an early prognostic, unfavourable sign of the disease. The significance of karyologic examination with exact classification of atypical leukemias is stressed.