Dentinogenesis imperfecta 1 (DGI1, MIM 125490) is an autosomal dominant dental disease characterized by abnormal dentin production and mineralization. The DGI1 locus was recently refined to a 2-Mb interval on 4q21 (ref. 1). Here we study three Chinese families carrying DGI1. We find that the affected individuals of two families also presented with progressive sensorineural high-frequency hearing loss (gene DFNA39). We identified three disease-specific mutations within the dentin sialophosphoprotein gene (DSPP) in these three families. We detected a G-->A transition at the donor-splicing site of intron 3 in one family without DFNA39, a mutation predicted to result in the skipping of exon 3. In two other families affected with both DGI1 and DFNA39, however, we identified two independent nucleotide transversions in exons 2 and 3 of DSPP, respectively, that cause missense mutations of two adjacent amino-acid residues in the predicted transmembrane region of the protein. Moreover, transcripts of DSPP previously reported to be expressed specifically in teeth are also detected in the inner ear of mice. We have thus demonstrated for the first time that distinct mutations in DSPP are responsible for the clinical manifestations of DGI1 with or without DFNA39.