CANDIDATE GENES FOR DG1 AND ADAI

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Relatively little in known about the molecular etiology of the human genetic diseases of enamel and dentin formation: amelogenesis imperfecta (AI), dentinogenesis imperfecta (DGI), and dentin dysplasia (DD). Linkage studies for autosomal dominant (AD) forms of AI, approximately 85% of all cases, have mapped only one type, local hypoplastic AI (AIH2), to human chromosome 4q21 within a 4 Mb region containing the genes for ameloblastin and enamelin. This same general region of 4q21 has been shown to contain the overlapping critical gene loci for three dentin diseases, DGI type II (DGI-II), DGI type III (DGI-III), and DD type II (DD-II). This overlapping region contains a dentin/bone "gene cluster", including osteopontin, bone sialoprotein, dentin matrix protein I, and dentin sialophosphoprotein. Mutational analysis studies have yet to establish the genes causing these diseases. The goal of this R01 continuation renewal is the delineation of the primary genetic defects that are responsible for the diseases DGI-II, DGI-III, DD- II, and the AD forms of AI. We will expand our efforts to include DD type II and other AD forms of AI through newly ascertained informative families. This study is based on the hypothesis that specific mutations within single dentin and enamel matrix proteins/proteinases have a causative role in the pathogenesis of DGI, DD and the AD forms of AI. To test this hypothesis we will ascertain informative families with these dental genetic diseases, establish or exclude linkage to the DGI/DD or AIH2 Critical disease loci on 4q21, and perform mutational analysis of potential candidate genes. Refined linkage studies will be performed on these disease loci through more extensive marker genotyping of additional families. ADAI families excluded from 4q2i, will be tested for linkage to other candidate enamel gene loci on chromosomes 1, 11, and 19, and the critical disease loci mapped. If ADAI families are excluded from linkage to all potential gene loci, a genome-wide search will be implemented. Finally, through positional cloning approaches identify potential new candidate tooth genes on 4q21 using constructed DGI/DD and AIH2 contigs. This information will contribute to our understanding of the molecular bases of these diseases, provide better diagnosis tools, increase our knowledge related to the function(s) of tooth proteins, and assisting in the design of treatment therapies.