SNP array plots of CNAs detected in the leukemic bone marrow of twins with concordant ETV6-RUNX1 fusion gene positive ALL. The ratio of loss of heterozygosity of the leukemic versus the matched remission sample is plotted on a logarithmic scale to estimate the copy number. Each dot represents the log₂ ratio of 1 SNP, with a moving average of 3 SNPs. The middle line represents a copy number of 2, the lower line a copy number of 1, and the top a copy number of 4. (A) 250K Sty SNP array analysis showing the short arm of chromosome 12 of twin set 2. Both twins have a deletion of 12p13.2, including the ETV6 gene (gray arrow); however, the boundaries and size of the deletion are different in each twin. (B) 250K Nsp plot of part of the long arm of chromosome 3 of twin set 1 showing a discordant deletion of 147 kb in region 3q13.2, which includes the BTLA and CD200 genes, seen in twin 1b, but not in twin 1a. (C) 250K Sty plot of part of the long arm of chromosome 2 of twin set 3 showing an identical gain of a 208-kb region at 2q33.3.