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August 1967

Chronic Myelocytic Leukemia and Identical Twins: Additional Evidence of the Philadelphia Chromosome as Postzygotic Abnormality

Author Affiliations

Oak Ridge, Tenn; Rochester, NY; Cooperstown, NY

From the Oak Ridge (Tenn) Institute of Nuclear Studies (Dr. Goh), the University of Rochester (NY) School of Medicine and Dentistry (Dr. Swisher), and the Mary Imogene Bassett Hospital, Cooperstown, NY (Dr. Herman).

Arch Intern Med. 1967;120(2):214-219. doi:10.1001/archinte.1967.00300020086011

IN 1960, Nowell and Hungerford demonstrated an abnormal chromosomal marker in chronic myelocytic leukemia (CML).1 This observation has been confirmed2-8 and the abnormal chromosome has been named Philadelphia or Ph1 chromosome.3 The mechanism of its production may be analogous to the production of a smaller G choromosome found in patients accidentally exposed to total-body irradiation.9 If so, it would indicate that the Ph1 chromosome is an acquired abnormality rather than a prezygotic abnormality. This postulation was supported by our finding that there was no Ph1 chromosome in a normal identical twin whose leukemic twin showed typical Ph1 chromosome.10 This communication reports the clinical and cytogenetic findings in another set of identical twins, one having CML; it also reports follow-up studies of the surviving normal identical twin of our first reported set10 7½ years after the diagnosis of CML in his

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