Novel dentin phosphoprotein frameshift mutations in dentinogenesis imperfecta type II.

The dentin sialophosphoprotein (DSPP) gene encodes the most abundant non-collagenous protein in tooth dentin and DSPP protein is cleaved into several segments including the highly phosphorylated dentin phosphoprotein (DPP). Mutations in the DSPP gene have been solely related to non-syndromic form of hereditary dentin defects. We recruited three Korean families with dentinogenesis imperfecta (DGI) type II and sequenced the exons and exon-intron boundaries of the DSPP gene based on the candidate gene approach. Direct sequencing of PCR products and allele-specific cloning of the highly repetitive exon 5 revealed novel single base pair (bp) deletional mutations (c.2688delT and c.3560delG) introducing hydrophobic amino acids in the hydrophilic repeat domain of the DPP coding region. All affected members of the three families showed exceptionally rapid pulp chambers obliteration, even before tooth eruption. Individuals with the c.3560delG mutation showed only mild, yellowish tooth discoloration, in contrast to the affected individuals from two families with c.2688delT mutation. We believe that these results will help us to understand the molecular pathogenesis of DGI type II as well as the normal process of dentin biomineralization.