Molecular Mapping of Uncharacteristically Small 5q Deletions in Two Patients with the 5q- Syndrome: Delineation of the Critical Region on 5q and Identification of a 5q- Breakpoint

Molecular mapping techniques have defined the region of gene loss in two patients with the 5q- syndrome and uncharacteristically small 5q deletions (5q31-q33). The allelic loss of 10 genes localized to 5q23-qter (centromere-CSF2-EGR1-FGFA-GRL-ADRB2-CSF1R-SPARC-GLUH1-NKSF1-FLT4-telomere) was investigated in peripheral blood cell fractions. Gene dosage experiments demonstrated that CSF2, EGR1, NKSF1, and FLT4 were retained on the 5q- chromosome in both patients and that FGFA was retained in one patient, thus placing these genes outside the critical region. GRL, ADRB2, CSF1R, SPARC, and GLUH1 were shown to be deleted in both patients. The proximal breakpoint is localized between EGR1 and FGFA in one patient and between FGFA and ADRB2 in the other, and the distal breakpoint is localized between GLUH1 and NKSF1 in both patients. Pulsed-field gel electrophoresis was used to map the 5q deletion breakpoints, and breakpoint-specific fragments were detected with FGFA in the granulocyte but not the lymphocyte fraction of one patient. This study has established the critical region of gene loss of the 5q- chromosome in the 5q- syndrome, giving the location for a putative tumor-suppressor gene in the 5.6-Mb region between FGFA and NKSF1.