Fusion of the COL1A1 and USP6 genes in a benign bone tumor

Aneurysmal bone cyst (ABC) is a benign intraskeletal cyst that often expands rapidly and shows a strong tendency to recur. Rearrangement of chromosome band 17p13 is a characteristic genetic feature of ABC, with t(16;17)(q22;p13) the most frequent chromosomal aberration. This translocation generates a CDH11–USP6 fusion gene in which the strong promoter of osteoblast cadherin 11 gene at 16q22 is fused to the entire ubiquitin-specific protease 6 coding sequence at 17p13. As a result, USP6 (alias Tre2) is transcriptionally upregulated. Fusion genes of several variant translocations have been reported in ABC, including a case with t(17;17) and COL1A1–USP6 fusion. In each translocation, the entire USP6 coding sequence is fused downstream to the promoter region of the partner gene. Here we report a second case of a bone tumor carrying a t(17;17) resulting in a COL1A1–USP6 chimeric gene. As in the previous case, exon 1 of COL1A1 was fused to exon 2 of USP6 in the chimeric transcript. A translation process of the hybrid transcript using the starting ATG codon of the COL1A1 gene results in a truncated, 38 amino acid residues variant of the COL1A1 peptide. Although a pathogenic effect of the small COL1A1 peptide cannot be ruled out, overexpression of USP6 through fusion with the COL1A1 promoter is a more reasonable hypothesis.