Fragment length analysis by capillary electrophoresis of cut V_κA27 PCR products (V_κA27 REHMA). Visualization of both TET- and FAM-coupled fragments was allowed, but only FAM fragments appeared in the shown length interval and are indicated in black. Size markers are not visualized for clarity reasons. Diagrams from top: patient no. 11 with a high-mutated fraction, followed by patient no. 4 with a low-mutated fraction, control no. 2 with a mutated fraction of 53%, and an unmutated cord blood sample. The peaks of 106 and 109 bp represent the quantity of V_κA27 fragments cleaved in one of the 2 hot-spot Fnu4HI restriction sites, respectively. The peaks of 244 bp represent the quantity of V_κA27 fragments cleaved in the signal peptide Fnu4HI site, but not cleaved in the hot spot as a consequence of one or 2 mutations eliminating the Fnu4HI sites. The peak of 271 bp (in general a fraction < 1%, as illustrated here) represents V_κA27 sequences in which cleavage is prevented by mutation in both the hot spot and the signal peptide restriction sites, as well.