ChromosomalDNACytophotometry in 20qâ€"Nonspecific Myeloid Disorders

DNAcytophotometry was used to quantify the chromosomal alterations in the bone marrowand blood of three patients with nonspecific myeloid disorders. All patients possesseda popu lation of cells with a morphologically abnormal chromosome 20, del(2OXqll).In two of the patients, the abnormal chromo some 20 showed nearly identical DNA measurementswith a net loss of 0.37% of the total autosomal DNA in one patient and 0.38% in the second. The third patient had a net loss of only 0.25% of the autosomalDNA.Analysisof the DNAcontent of the long arm and short arm of the abnormalNo. 20 indicated that all three cases had chromosomal material added to the short arm (0.10 to 0.14% of the autosomalDNA).About 0.50% of the autosomal DNAwas deleted from the long arm in two of the patients; only 0.35% of the autosomal DNA was deleted from the long arm in the third case. Withinthe limit of resolution, there is no evidencethat the materiallost hasbeentranslocated intact to another chromosome. The origin of the 20qâ€"chro mosomeas the result of an incomplete pericentric inversion is suggested.