Location of the breakpoints withinMALT1and theIGHlocus. (A) Sequence of the der(14)t(14;18)(q32;q21) breakpoint from case 1 (GenBank accession no. pending). Chromosome 18q21 sequences shown in bold, IGH sequences underlined, inserted nontemplated nucleotides in italics. DNA sequence analysis of cloned LDI-PCR product from case 1 showed loss of homology with IGH sequences beyond IGHJ5. The sequence beyond IGHJ5 was identical to sequence from BAC clone RP11-126O1, which contained not only both breakpoints but also the 5′ end of the MALT1 gene as well. (B) Ideogram to show the localization of chromosome 18q21 breakpoints. Both cloned breakpoints fell 5′ (centromeric) of the most 5′ exon of the database consensus MALT1 gene sequence (http://www.ncbi.nlm.nih.gov/entrez/viewer.fcgi?val=NP_006776.1). However, it should be noted that one report has indicated the presence of alternative 5′ MALT1 exons¹⁵ ; these are depicted as exons 1a and 1b. Neither of these exons is coding and therefore the open-reading frame of MALT1 is maintained in both translocations. Within the BAC clone RP11-126O1, the breakpoints were located at nucleotides 27 558 (case 1), and 28 209 (case 2), thus placing the breakpoints 1.1 and 1.7 kb upstream, respectively, of the first 5′ MALT1 exon.