The chromosomes were examined in 15 male patients and 3 female patients with chronic lymphocytic leukemia and, for comparison, in 10 normal men and 5 normal women. All had grossly normal chromosomes, but analysis of the lengths of chromosomes Nos. 1, 2, 21, 22, and Y showed that the small acrocentric chromosomes, Nos. 21, 22, and Y collectively, were significantly shorter in leukemic men than in normal men, and a similar but nonsignificant difference in chromosomes Nos. 21 and 22 was present in leukemic and normal women. No one chromosome was abnormally small, and the shortness was probably due to a greater degree of spiralization and condensation of all or some of the small acrocentric chromosomes. This might be a secondary effect of the leukemia, or alternatively, the greater condensation of the chromosomes, with associated modification or suppression of the action of genes carried thereon, could be a fundamental lesion closely concerned with the cause of chronic lymphocytic leukemia.

It is suggested that such heteropyknotic chromosomes may be the dense nuclear condensations characterizing the Grumelée cell found in chronic lymphocytic leukemia.

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