A marrow chromosomal abnormality preceding clinical leukemia in Down's syndrome.
D001856:Bone Marrow Examination; D002869:Chromosome Aberrations; D025063:Chromosome Disorders; D004314:Down Syndrome / Q000150:complications*; D006801:Humans; D007223:Infant; D007621:Karyotyping; D007938:Leukemia / Q000175:diagnosis* / Q000209:etiology*