Loss of expression of FGFR3 in t(4;14) myeloma is a result of loss of der(14). (A) A copy number plot output from CNAG showing an example of a t(4;14) sample without expression of FGFR3 with decreased copy number at 4p16-ptel on chromosome 4 and on chromosome 14. The enlarged area shows the approximate positions of the breakpoints in the 4 samples without FGFR3 expression (down arrows). (B) As above but for a t(4;14) sample with FGFR3 over-expression. (C top panel) IgH-MMSET cDNA products from each t(4;14) sample, with or without loss of der(14), and controls H929 (t(4;14) positive) and MM1s (t(4;14) negative). Bands at 1000, 400 and 200 bp correspond to MB4-1, MB4-2 and MB4-3 breakpoint products. (Bottom panel) ABL control cDNA PCR. (D) Expression levels of FGFR3 and MMSET in the t(4;14) samples by microarray. (E) A model explaining the loss of FGFR3 expression in a sample with a t(4;14) translocation through deletion of der(14) chromosome (see “Results” for details). F = FGFR3 locus, M = MMSET locus.