Differential Effects of DLX3 Mutations Drive Phenotypic Variability in Tricho‐Dento‐Osseous Syndrome via Direct Activation of WNT10A

DLX3 is a homeobox transcription factor essential for multiple organogenesis processes. Mutations in DLX3 cause trichodentoosseous syndrome (TDO), characterized by curly hair, sclerotic bone, enamel, and dentin defects as well as taurodontism. Phenotypic variability in TDO has been well documented, but its pathogenesis remains poorly understood. Here, we characterized three TDO families with distinct clinical features and identified a known DLX3 deletion (c.561_562del) and the first pathogenic splice-site variant (c.516+1_516+2insA). The proband with the splice-site mutation displayed a mesenchymal-dominant phenotype with severe dentin hypoplasia, enlarged pulp chambers, and hypertaurodontism but nearly normal enamel, whereas the mother and sister showed epithelial-dominant anomalies, including enamel hypoplasia and kinky hair. Minigene analysis demonstrated that c.516+1_516+2insA generated two aberrant transcripts encoding p.Val173Aspfs*28 and p.Arg120_Val173del. These mutant proteins localized mainly in the cytoplasm and showed markedly reduced transactivation activity. In cultured human dental pulp cells, DLX3 overexpression upregulated the odontoblastic markers DSPP, MMP20, and WNT10A. Chromatin immunoprecipitation and reporter assays further revealed that DLX3 directly activates WNT10A via a conserved enhancer (chr2:218,878,973_218,879,302) and three upstream binding sites. These findings expand the TDO mutational spectrum and suggest that differential mutant DLX3 expression may contribute to phenotypic variability, whereas disrupted regulation of WNT10A underlies dentin defects and taurodontism.