Isochromosomes in acute lymphoblastic leukaemia: i(21q) is a significant finding.
The incidence, type, and clonality of isochromosomes at diagnosis were investigated in acute lymphoblastic leukaemia (ALL). An isochromosome was detected in 50/1,035 (4.8%) of successfully karyotyped patients, 41/919 children (4.5%) and 9/116 adults (7.8%), who were diagnosed within a 5 year period. Isochromosomes of 21q with breakpoints in the short arm at p11 or in the long arm at q10 or q22 were identified in 15 patients (1.4%) associated with B-lineage immunophenotype, a white blood cell count (WBC) of < 10 x 10(9)/litre, and pseudo- or low hyperdiploidy. Isochromosomes of 17q and 7q occurred in 13 (1.3%) and 9 (0.9%) patients, respectively, and were associated with high hyperdiploidy. Isochromosomes of 9q and 6p occurred in 6 (0.6%) and 5 (0.5%) patients, respectively, whereas i(Xp), i(lq), and i(8q) occurred in I patient each. The isochromosome occurred as the sole abnormality in 4 patients [3 with i(21q) and I with i(7q)] and in the stemline, but with other chromosomal changes, in 35 patients. It was confined to a clonally evolved sideline in II patients. Isochromosomes occurred with established abnormalities in 7 patients: with t(1;19)-i(7q)/i(9q)/i(7q) and i(9q) each in I patient; with t(4;11)-i(7q)/i(17q) in 1 and 2 patients, respectively; and with t(9;22)-i(9q) in I patient. This study indicates that isochromosome formation can be an early chromosomal change and suggests that i(21q) occurs more frequently at diagnosis than has been previously suspected.
Haematology Department, Royal Free Hospital School of Medicine, London, United Kingdom.
M
M
Martineau
R
R
Clark
D M
DM
Farrell
J M
JM
Hawkins
A V
AV
Moorman
L M
LM
Secker-Walker
D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D002886:Chromosomes, Human, Pair 17; D002891:Chromosomes, Human, Pair 21; D002897:Chromosomes, Human, Pair 7; D002899:Chromosomes, Human, Pair 9; D004171:Diploidy; D005260:Female; D006801:Humans; D016130:Immunophenotyping; D007223:Infant; D018404:Isochromosomes; D007621:Karyotyping; D008297:Male; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000235:genetics* / Q000276:immunology