Fusion of the HMGA2 and C9orf92 genes in myolipoma with t(9;12)(p22;q14)

Ioannis Panagopoulos, Ludmila Gorunova, Antonio Agostini, Ingvild Lobmaier, Bodil Bjerkehagen, Sverre Heim

Myolipoma of soft tissue is an extremely rare benign tumor composed of mature adipose tissue and smooth muscle cells. It is found predominantly in women. The cytogenetic and molecular genetic features of myolipomas remain largely unexplored. Here we present the first cytogenetically analyzed myolipoma. Cytogenetic and molecular genetic analyses were done on a myolipoma. G-banding analysis of short-term cultured cells from the myolipoma yielded a karyotype with a single clonal chromosome abnormality: 46,XX,t(9;12)(p22;q14). Fluorescence in situ hybridization experiments demonstrated that HMGA2 (in 12q14) was rearranged. Molecular genetic analysis showed that the translocation resulted in fusion of HMGA2 with the C9orf92 gene (from 9p22). The HMGA2-C9orf92 fusion transcript would code for a putative protein containing amino acid residues 1-94 of HMGA2 and 6 amino acid residues from the out-of-frame fusion with exon 4 of C9orf92. The pattern of HMGA2 rearrangement in the present case of myolipoma is similar to what is found in other benign connective tissue tumor types, including lipomas, i.e., disruption of the HMGA2 locus leaves intact exons which encode the AT-hook domains but separates them from the 3´-terminal part of the gene. Whether any genetic features differentiate myolipomas from regular lipomas with HMGA2-involvement is a question that cannot be answered until more cases of the former tumor type are subjected to genetic analysis.