Delineation of the minimal region of loss at 13q14 in multiple myeloma.

Previous studies have focused on the incidence and prognostic implications of 13q14 deletions in multiple myeloma (MM), but none has sought to delineate the minimal common deleted region (CDR). In an effort to do so, dual-color interphase fluorescence in situ hybridization (FISH) was applied on 82 myeloma cases, initially by use of three probes for 13q14 (RB1, D13S319, and D13S25). Deletions were detected in 29/82 (35.4%) cases, and all except one were monoallelic. Subsequently, contiguous YACs, PACs, and a BAC spanning the 13q14-q21 region were employed for deletion mapping in addition to a 13q telomere probe. Large deletions extending to the 13q34 region were found in 55% of the deleted cases, whereas an additional 13.8% showed loss of both 13q34 and 13q14 regions with retention of 13q21. A CDR of approximately 350 kb was identified at 13q14 with the proximal border approximately 120 kb centromeric from D13S319, encompassing an area rich in expressed sequence tagged sites and containing DLEU1, DLEU2, and RFP2 genes. Direct sequencing of the RFP2 gene revealed no mutations in six patients and four MM cell lines harboring deletions of the CDR. However, a role for RFP2 in the pathogenesis of MM cannot yet be excluded, given that alternative mechanisms such as haploinsufficiency remain possible. Copyright 2002 Wiley-Liss, Inc.