A novel splice mutation induces exon skipping of the EXT1 gene in patients with hereditary multiple exostoses.

The molecular mechanism of hereditary multiple exostoses (HME) remains ambiguous and a limited number of studies have investigated the pathogenic mechanism of mutations in patients with HME. In the present study, a novel heterozygous splice mutation (c.1284+2del) in exostosin glycosyltransferase 1 (EXT1) gene was identified in a three‑generation family with HME. Bioinformatics and TA clone‑sequencing indicated that the splice site mutation would result in exon 4 skipping. Reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) revealed that the expression levels of wild‑type EXT1/EXT2 mRNA in patients with HME were significantly decreased, compared with normal control participants (P<0.05). Abnormal EXT1 transcript lacking exon 4 (EXT1‑DEL) and full‑length EXT1 mRNA (EXT1‑FL) were overexpressed in 293‑T cells and Cos‑7 cells using lentivirus infection. RT‑qPCR demonstrated that the expression level of EXT1‑DEL was significantly increased, compared with EXT1‑FL (17.032 vs. 6.309, respectively; P<0.05). The protein encoded by EXT1‑DEL was detected by western blot analysis, and the level was increased, compared with EXT1‑FL protein expression. Immunofluorescence indicated that the protein encoded by EXT1‑DEL was located in the cytoplasm of Cos‑7 cells, which was consistent with the localization of the EXT1‑FL protein. In conclusion, the present study identified a novel splice mutation that causes exon 4 skipping during mRNA splicing and causes reduced expression of EXT1/EXT2. The mutation in EXT1‑DEL generated a unique peptide that is located in the cytoplasm in vitro, and it expands the mutation spectrum and provides molecular genetic evidence for a novel pathogenic mechanism of HME.