(A) FISH analysis of two nuclei from patient no. 1 with cosmids 179A6 (detected with rhodamine) and 148B6 (detected with FITC), which hybridize to ETV6 exons 1 and 8, respectively. Colocalized signals indicate the normal ETV6 allele, while separate red and green signals indicate a break within ETV6. (B) Three nuclei from patient no. 1 hybridized with cosmids 179A6 (detected with rhodamine) and ICRFc108G2043QD2 (CDX2 exon 1 plus upstream sequence, detected with FITC). Colocalization of these cosmids indicates a chromosome 13 break upstream of CDX2 exon 1.