Our working paradigm is that there is a genetic basis to human disease and that understanding the genetic basis of disease will foster development of better diagnostic and treatment strategies. We study Mendelian diseases to identify the underlying gene defect and to understand how the product(s) of this/these gene mutation(s) result in abnormal development or disease. In some cases we have developed animal models (transgenic mice) and in vitro cell models to study disease pathogeneses. Dentinogenesis imperfecta (DI) (10% effort): Genetic mutations of the dentin sialophosphosphoprotein (DSSP) gene are responsible for most cases of DI and dentin dysplasia (DD). Dentin, the most abundant tissue in teeth, is produced by odontoblasts, which differentiate from mesenchymal cells of the dental papilla. Dentin defects are broadly classified into two major types: DIs, types I-III and dentin dysplasias (DDs, types I and II). To date, mutations in DSPP have been found to underlie DI types II and III and DD type II. With the elucidation of the underlying genetic mechanisms has come the realization that the clinical characteristics associated with DSPP mutations appear to represent a continuum of phenotypes. (Hart &Hart, Ortho Craniofac Res, 2009). Recent work (McKnight et al, Hum Mut, 2008) describing studies of 9 families segregating DI or DD has substantiated that the clinical characteristics associated with DSPP mutations appear to represent a continuum of phenotypes. Additionally, studies of Mendelian syndromes with dental findings have determined that mutations of other genes can cause dentin defects including GALNT3 mutations (Dumitrescu et al 2009) and DLX3 mutations. Understanding the genetic basis of diseases of dental importance provides an important first step to the development of diagnostic and treatment strategies to provide better care for affected individuals. To effectively translate clinical and research findings it will also be necessary to develop more effective strategies to educate dental health care clinicians in the field of genetics. (Johnson et al, J Dent Educ, 2008). Tricho-dento-osseous syndrome (TDO) (20 % effort). DLX3 mutations are responsible for TDO which is clinically characterized by anomalies of tooth, hair and bone. A cardinal feature of TDO is an increased thickness and density of bone. To characterize how mutant DLX3 contributes to alterations of bone we generated a transgenic model with mice carrying the 4bp DLX3 mutation driven by a collagen 1A1 promoter. Microcomputed tomographic analyses demonstrated markedly increased trabecular bone volume and bone mineral density in femora from TG mice. In ex vivo experiments, TG mice showed enhanced differentiation of bone marrow stromal cells to osteoblasts and increased expression levels of bone formation markers. However, TG mice did not show enhanced dynamic bone formation rates in in vivo fluorochrome double labeling experiments. Osteoclastic differentiation capacities of bone marrow monocytes were reduced in TG mice in the presence of osteoclastogenic factors and the numbers of TRAP(+) osteoclasts on distal metaphyseal trabecular bone surfaces were significantly decreased. TRACP 5b and CTX serum levels were significantly decreased in TG mice, while IFN-gamma levels were significantly increased. These data demonstrate that increased levels of IFN-gamma decrease osteoclast bone resorption activities, contributing to the enhanced trabecular bone volume and mineral density in these TG mice. These data suggest a novel role for this DLX-3 mutation in osteoclast differentiation and bone resorption. (Choi et al, Dev Biol. 2009). Amelogenesis Imperfecta (AI) (20%effort): We continue to study families segregating the AI phenotype. AI is caused by AMEL, ENAM, MMP20 and KLK4 gene mutations. Mice lacking expression of the AmelX, Enam and Mmp20 genes have been generated, providing tools to better understand enamel formation and AI pathogenesis. (Wright et al., Cells Tissues Organs, 2009). We have continued our linkage studies of families segregating AI to further characterize genotype-phenotype correlations for AI and increase the diagnostic potential for genetics to provide a definitive diagnosis for individuals with AI, a step towards integrating diagnostic testing with care and access to care. We have expanded on the identification of FAM83H gene mutations etiologic for autosomal dominant AI (ADAI) (Hart et al, Clin Genet, 2009). Additionally, our studies of families segregating ADAI have identified multiple novel FAM83H mutations were identified, including two 2-bp-deletion mutations, the first non-nonsense mutations identified. Craniofacial deviation from normal was more prevalent in the affected individuals. Affected individuals having truncating FAMH3H mutations of 677 or fewer amino acids presented a generalized ADHCAI phenotype, while those having mutations capable of producing a protein of at least 694 amino acids had a unique and previously unreported phenotype affecting primarily the cervical enamel. This investigation shows that unique phenotypes are associated with specific FAM83H mutations. (Wright et al, J Dent Res, 2009). Studies of families segregating AI have also provided direct evidence for the existence of at least one additional, currently unidentified gene locus etiologic for ADAI. (Becerik et al, AM J Med Genet, 2009). We have characterized dental/oral and craniofacial findings in a number of genetic syndromes (30% effort). These studies are performed based on genetic referrals to the NIDCR intramural dental clinic as well as with participation in the NIH Clinical Center Undiagnosed Diseases Program. Through our studies we have continued to characterize orofacial and dental findings in a number of rare diseases and syndromes including Hutchinson-Gilford progeria (Domingo et al, Oral Dis, 2009). Additionally, our studies of Mendelian syndromes continue to expand and more fully document dental findings of importance. We have characterized enamel defects in patients with methylmalonic acidemia (MMA) and cobalamin (cbl) metabolic disorders. (Bassim et al, Oral Diseases, 2009). Our studies have determined that enamel defects are significantly more prevalent in MMA affected individuals, across complementation types (P <0.0001). The mut MMA subgroup show a significantly higher prevalence of severe enamel defects, and individuals with enamel defects exhibited higher serum methylmalonate levels. These findings suggest an association between enamel developmental pathology and disordered metabolism. Salivary methylmalonate levels were extremely elevated and were significantly higher in MMA affected individuals than controls, indicating that salivary testing may be an effective diagnostic strategy. Through our studies of human cleft lip/palate we have identified and validated a SNP in the PDGF-C gene that is associated with CL/P. The presence of the -986T allele in the PDGF-C promoter is associated with a significant decrease (up to 80%) of PDGF-C gene promoter activity. This functional polymorphism acting on a susceptible genetic background may represent a component of human CL/P etiology.(Choi et al, Eur J Hum Genet 2009) Hereditary Gingival Fibromatosis/Gingival overgrowth conditions (20%). We have continued our studies of gingival overgrowth conditions to identify novel genetic loci etiologic for syndromic forms of the condition. As part of these studies we are characterizing tissue and cell specific gene expression profiles to increase our understanding of the physiology of gingival tissues. The goal of these studies is to increase our ability to diagnose and treat these conditions as well as to understand unique qualities of gingival tissues such as their increased wound healing capabilities. (Hart &Hart, Ortho Craniofac Res, 2009).
Showing the most recent 10 out of 15 publications
