FGFR3 gene translocation and mutation screening in MM patients. (A) Detection of immunoglobulin heavy chain (IgH)/MMSET fusion product using translocation-specific RT-PCR⁵  (a lanes represent MMSET + JH PCR, whereas b lanes represent MMSET + 1 m PCR). Of 24 patient samples, 22 are positive: 5 patients have a translocation breakpoint as in the myeloma cell line KMS11, 9 patients have a breakpoint like H929, and 8 patients have an OPM2 breakpoint. (B) Genetic changes of FGFR3 gene in patient samples. (i) Sequence analysis of cloned cDNA of patient no. 1 revealed a 6-bp insertion of 5′-AACAGT-3′ at nucleotide position 1306, resulting in an insertion of amino acids threonine and cysteine. (ii) Point mutation at nucleotide 761A>G resulting in tyrosine to cysteine change in FGFR3 codon 241 (patient no. 23, sequencing from reverse direction of the gene). (iii) Of 22 patient samples, 17 carry C to T transition in FGFR3 codon 294. (C) Different isoforms of FGFR3 are detected in patient nos. 15 and 16. Patient nos. 15 and 16 expressed the FGFR3 IIIc isoform (upper band) and novel isoforms devoid of Ig-like domain I and of both domain I and the acid-box, respectively, (lower band) while patient no. 18 expressed only FGFR3 IIIc isoform.