Genetics of hypodiploid less than 40 chromosomes ALL. (A) Modal numbers of all 218 hypodiploid ALL cases with <40 chromosomes reported in the literature, ascertained from the Mitelman Database of Chromosome Aberrations and Gene Fusions in Cancer.7 Cases where the modal number was given as a range, with a known T-cell immunophenotype, or with t(1;19)(q23;p13), t(9;22)(q34;q22), or t(14;18)(q32;q21) were excluded from the analysis. There are 2 clear peaks centered on 27 and 36 chromosomes, corresponding to near-haploid and low-hypodiploid ALL, respectively. Chromosomal patterns are shown in blue, constitutional mutations in dark blue, and somatic mutations in purple. (B) Chromosomal doubling is frequent in both near-haploid and low-hypodiploid ALL, sometimes leading to masked hypodiploidy (ie, only the clone with doubled chromosomes are detected). The relative proportions of the founder and doubled clone often differ between diagnosis and relapse, with the doubled clone generally dominating at diagnosis and the founder clone at relapse. Professional illustration by Somersault18:24.
