Acute lymphoblastic leukemia with trisomy 21 constitutional mosaicism.

Abstract 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.