Chromosome abnormalities in human cancer. Report of a patient with chronic myelocytic leukemia and his nonleukemic monozygotic twin

Chromosome studies were made on a 31‐year‐old man (H. vG.) with chronic myelocytic leukemia and his normal identical twin (L. vG.). Identical blood typing factors (17 tested) and similar fingerprint analyses warrant the conclusion that the twins are monozygous. Characteristic Ph1 chromosomes were found in blood and bone marrow from H.vG. before and after treatment with the colchicine analog, trimethyl colchicinic acid. During therapy the white blood count decreased from nearly 400,000/mm3 to less than 10,000/mm3. By contrast, analyses of blood and fresh bone marrow from L.vG. were consistently negative for the Ph1 chromosome. These results reinforce the postulate that the Ph1 chromosome is an acquired abnormality rather than a hereditary defect of the chromosome.