NFIB rearrangement in superficial, retroperitoneal, and colonic lipomas with aberrations involving chromosome band 9p22

Abstract

Lipomas are frequently characterized by rearrangements resulting in the fusion of the HMGA2 gene (12q14.3) with a variety of partners. Chromosome band 9p22 rearrangements occur in about 1% of lipomas. We report here the molecular cytogenetic analysis of five cases of lipoma with a 9p22 aberration, including the first cytogenetic analysis of a colonic lipoma. Three out of the five cases showed a rearrangement of NFIB at 9p22.3. The NFIB rearrangement involved a fusion with HMGA2 in two cases. We have identified an in-frame fusion of the first three exons of HMGA2 with exon 6 of MSRB3 (12q14.3) and exons 8 and 9 of NFIB by using 3'RACE-PCR in a case of superficial lipoma. In a case of retroperitoneal lipoma we found a fusion of HMGA2 with NFIB by fluorescence in situ hybridization analysis. The colonic lipoma was characterized by a t(9;16;19)(p22;q21;q13) with a rearrangement of NFIB and no rearrangement of HMGA2. NFIB belongs to the nuclear factor I transcription family. It has been previously shown to be fused with HMGA2 in one case of lipoma and to be a recurrent partner of HMGA2 in pleormorphic adenoma of salivary glands. We here demonstrate that NFIB can also be rearranged independently from HMGA2, indicating a potentially important role in lipoma pathobiology. Our findings suggest that the rearrangement of NFIB might be associated with deep-seated lipomas, such as retroperitoneal or gastro-intestinal lipomas.