Targeted Next-Generation Sequencing Newly Identifies Mutations in Exostosin-1 and Exostosin-2 Genes of Patients with Multiple Osteochondromas.

Multiple osteochondromas (MO) is one of the most common benign bone tumors in humans with an autosomal dominant hereditary mode. MO is a genetic heterogeneity disease with variable number and size of osteochondromas, as well as changeable number and location of diseased bones. Mutations in Exostosin-1/Exostosin-2 (EXT1/EXT2) genes are the main molecular basis of MO. EXT1 and EXT2 genes encode exostosin 1 and exostosin 2, respectively, both of which are transmembrane glycosyltransferases that elongate the chains of heparin sulfate (HS) at HS proteoglycans (HSPGs). HSPGs are considered to be involved in regulating the proliferation and differentiation of chondrocytes. Owing to large size of EXT1/EXT2 genes and lack of mutation hotspots, molecular diagnosis of MO is challenging. Here, we applied targeted next-generation sequencing (t-NGS) in mutation screening of EXT1/EXT2 genes for 10 MO patients. The results were compared and validated with Sanger sequencing. Overall, nine mutations identified by t-NGS were confirmed with Sanger sequencing, excluding two variants of false positive, suggesting the reliability of mutation screening by t-NGS. The nine mutations identified by t-NGS include two missense mutations (EXT1: c.1088G>A and c.2120C>T), one splicing mutation (EXT2: c.744-1G>T), and six nonsense mutations (EXT1: c.351C>G, c.1121G>A, and c.1843_1846dup; EXT2: c.67C>T, c.561delG, and c.575T>A). In summary, our paper provides the primary data of the application of t-NGS in MO molecular diagnosis, including six newly identified mutations (EXT1: c.1843_1846dup, c.1088G>A, c.351C>G, and c.2120C>T and EXT2: c.744-1G>T and c.575T>A), which further enrich the mutation database of MO from the Chinese population.