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 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 virto cell models to study disease pathogeneses. ? Dentinogenesis imperfecta (DI) (15% effort): Genetic mutations of the dentin sialophosphosphoprotein (DSSP) gene are responsible for 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 2007). Recent work (McKnight et al 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. Within nine DDtype II and DI type II and III patients, seven have 1 of 4 net -1 deletions within the approximately 2-kb coding repeat domain of the DSPP gene while the remaining two patients have splice-site mutations. All frameshift mutations are predicted to change the highly soluble DSPP protein into proteins with long hydrophobic amino acid repeats that could interfere with processing of normal DSPP and/or other secreted matrix proteins. We propose that all previously reported missense, nonsense, and splice-site DSPP mutations (all associated with exons 2 and 3) result in dominant phenotypes due to disruption of signal peptide-processing and/or related biochemical events that also result in interference with protein processing. ? Amelogenesis Imperfecta (AI) (30%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. These models provide tools for understanding enamel formation and AI pathogenesis. We determined human AI phenotypes in a clinical population of 463 AI affected individuals from 54 families were evaluated and mutations in the AMEL, ENAM and KLK4 genes identified. The majority of human mutations for genes coding enamel nonproteinase proteins (AMEL and ENAM) resulted in variable hypoplasia ranging from local pitting to a marked, generalized enamel thinning. Specific AMEL mutations were associated with abnormal mineralization and maturation defects. Amel and Enam null murine models displayed marked enamel hypoplasia and defective mineral crystal structure. Human mutations in genes coding for the enamel proteinases (MMP20 and KLK4) cause variable degrees of hypomineralization. The murine Mmp20 null mouse exhibits both hypoplastic and hypomineralized defects. Amel and Enam mouse models for AI exhibit enamel phenotypes (hypoplastic) that are similar to those in humans. Mmp20 null mice have a greater degree of hypoplasia than humans with MMP20 mutations. Mice lacking expression of the currently known genes associated with the human AI conditions provide useful models for understanding the pathogenesis of these conditions.(Wright et al 2008). ? Not all AI causing mutations have been identified. We studied 8 Turkish kindreds with autosomal dominant hypoplastic AI and identified FAM83H mutations in all 8 families. A total of 3 different FAM83H nonsense mutations; a p.Q398X mutation and 2 novel nonsense mutations, p.Q444X and p.Q456X, were detected. These findings indicate that FAM83H mutations may be responsible for the majority of autosomal dominant hypocalcified amelogenesis imperfecta in the Turkish population. As the most predominant form of autosomal dominant AI, these findings have important implications for the implementation of genetic testing to confirm this clinical diagnosis. (Hart et al 2008 In Press).? TDO studies-45%effort:Tricho-dento-osseous syndrome (TDO) due to DLX3 mutations is characterized by anomalies of tooth, hair and bone. A cardinal feature of TDO is an increased thickness and density of bone. We tested the effects of the DLX3 gene mutation responsible for TDO on the osteoblastic differentiation of preosteoblastic MC3T3E1 cells and multipontent mesenchymal C2C12 cells. Transfection of wild type DLX3 into MC3T3E1 and C2C12 cells increased alkaline phosphatase-2 activity, mineral deposition, and promoter activities of the osteocalcin and type 1 collagen genes. Transfection of mutant DLX3 into these cells further enhanced alkaline phosphatase activity, mineral deposition, and osteocalcin promoter activities, but did not further enhance type 1 collagen promoter activity. Transfection of mutant DLX3 into C2C12 cells markedly down regulated desmin gene expression, and protein expression of desmin and MyoD, while increasing protein expression of osterix and Runx2. These results demonstrate that the DLX3 deletion mutation associated with TDO enhances mesenchymal cell differentiation to an osteoblastic lineage. (Choi et al 2008). As in vitro findings do not always recapitulate the true in vivo biology, we generated a transgenic model with mice carrying the 4bp DLX3 mutation driven by a collagen 1A1 promoter. Studies are ongoing to characterize the biologic mechanism by which this DLX3 mutation results in beneficial bone changes and pathologic changes in the enamel, dentin and pulp.? We have characterized dental/oral and craniofacial findings in a number of rare genetic syndromes (10% effort) Hyperimmunoglobulin-E syndrome (HIES) is a primary immunodeficiency characterized by eczema, recurrent infections, and extremely elevated serum immunoglobulin-E. Non-immunologic findings include characteristic facial features (prominent forehead, fleshy nasal tip, and increased interalar distance); skeletal involvement (pathological fractures, scoliosis, and craniosynostosis); and retention of primary teeth. We characterized intraoral soft tissue findings in 60 HIES patients. Our study revealed the presence of lesions of the hard palate and dorsal tongue in 55% and 60% of patients, respectively. Palatal lesions ranged from a generalized surface keratosis to a midline sagittal fibrotic bridge. Tongue lesions consisted of multiple fissures and a midline cleft. On the lip and buccal mucosa, keratotic plaques and/or surface fissures were found in 8% and 23% of patients, respectively. Manifested in 76.7% of patients, the intraoral lesions were significantly more prevalent than the characteristic facial traits (P=0.0013). These findings indicate that alterations in oral mucosa and gingiva were present in the majority of HIES patients. These novel intraoral findings may facilitate the diagnosis of HIES. (Domingo et al 2008).? Hutchinson-Gilford progeria syndrome is a rare, sporadic, autosomal dominant syndrome withpremature aging, generally leading to death at 13 years of age due to myocardial infarction or stroke. We participated in a multi institute NIH study to characterize the natural history of progeria patients. 15 children representing nearly half of the world's known patients with Hutchinson-Gilford progeria syndrome were evaluated as part of a comprehensive clinical protocol at NIH. Oral abnormalities characterized included hypodontia (most often, missing second premolars), tongue-tie, high arch palate, double rows of teeth, and delayed tooth eruption. (Merideth et al 2
| Wright, J T; Frazier-Bowers, S; Simmons, D et al. (2009) Phenotypic variation in FAM83H-associated amelogenesis imperfecta. J Dent Res 88:356-60 |
| Domingo, D L; Trujillo, M I; Council, S E et al. (2009) Hutchinson-Gilford progeria syndrome: oral and craniofacial phenotypes. Oral Dis 15:187-95 |
| Bassim, C W; Wright, J T; Guadagnini, J P et al. (2009) Enamel defects and salivary methylmalonate in methylmalonic acidemia. Oral Dis 15:196-205 |
| Hart, T C; Hart, P S (2009) Genetic studies of craniofacial anomalies: clinical implications and applications. Orthod Craniofac Res 12:212-20 |
| Domingo, D L; Freeman, A F; Davis, J et al. (2008) Novel intraoral phenotypes in hyperimmunoglobulin-E syndrome. Oral Dis 14:73-81 |
| Su, C-Y; Corby, P M; Elliot, M A et al. (2008) Inheritance of occlusal topography: a twin study. Eur Arch Paediatr Dent 9:19-24 |
| Merideth, Melissa A; Gordon, Leslie B; Clauss, Sarah et al. (2008) Phenotype and course of Hutchinson-Gilford progeria syndrome. N Engl J Med 358:592-604 |
| Choi, Sun Jin; Song, In Sun; Ryu, Ok Hee et al. (2008) A 4 bp deletion mutation in DLX3 enhances osteoblastic differentiation and bone formation in vitro. Bone 42:162-71 |
| Johnson, Lynn; Genco, Robert J; Damsky, Caroline et al. (2008) Genetics and its implications for clinical dental practice and education: report of panel 3 of the Macy study. J Dent Educ 72:86-94 |
| Doherty, Emily S; Lacbawan, Felicitas; Hadley, Donald W et al. (2007) Muenke syndrome (FGFR3-related craniosynostosis): expansion of the phenotype and review of the literature. Am J Med Genet A 143A:3204-15 |
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