Differences in CTG triplet repeat expansion in leukemic cells and normal lymphocytes from a 14-year-old female with congenital myotonic dystrophy.

We describe a rare case of acute lymphoblastic leukemia in a 14-year-old female with congenital myotonic dystrophy manifested as mental retardation, extensive contractures of multiple joints of the lower extremities, and severe scoliosis. Because of the potential toxicity of chemotherapy and the patient's poor performance status, a modified chemotherapy regimen was administered. Analysis of the greatly expanded number of CTG repeats at the 3' untranslated region of DMPK gene showed that the number of repeats was 233 greater in leukemic cells than in normal lymphocytes; this elongation may have occurred during the cellular proliferation of leukemic clones.