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Do Genes Cause Caries? NYU Dental Researchers Study Twins for Clues

A pair of identical twins develops caries on the same tooth surfaces over the course of several years. Their dentist wonders: how much of a role does genetics play in this pattern?

In an effort to explain how genetics and the environment interact in caries development, NYU dental researchers Dr. Walter Bretz and Dr. Patricia Corby have assembled 1,100 pairs of twins -- the largest group of twins ever gathered for oral health research -- to assess the relative significance of 15 potential factors in caries development, including anatomical problems, such as porous enamel and deep pits and fissures; salivary protein profiles; oral bacteria levels, sucrose taste preferences and other factors linked to both genetics and the environment; as well as socioeconomic concerns, such as a lack of access to fluoridated water and dental care. By the conclusion of their five-year study, funded by a $1.7 million grant from the National Institute of Dental and Craniofacial Research (NIDCR), the researchers will develop a risk assessment equation that assigns numerical values to various factors in caries development.

The 1,100 twin pairs assembled by Dr. Bretz and Dr. Corby, both natives of Brazil, include both male and female identical and fraternal twins up to 21 years of age living in disadvantaged neighborhoods in the northeastern Brazilian city of Montes Claros, where inadequate water fluoridation and inability to access dental care put residents at risk for caries.

Because they live together and have similar dietary habits and health practices, twins are considered excellent subjects for research that compares caries development in people of the same age from similar environments.

One method used to identify a genetic predisposition to caries is to compare identical twins who share all their genes against fraternal ones, who share an average of half their genes. If identical twins tend to develop caries one way, while fraternal twins show no equivalent pattern, investigators may infer that genetics plays a leading role. Conversely, if caries development follows similar patterns in both identical and fraternal twins, environmental factors may be the chief factor.

Preliminary results from the study support a strong role for genetics. For example, the researchers observed high levels of caries-causing bacteria in identical twin pairs, but no similar level of colonization in fraternal pairs.

Working in collaboration with Dr. Thomas Hart, a geneticist at the NIDCR, Dr. Bretz and Dr. Corby also will conduct research that identifies specific genes contributing to caries. Ultimately, this research could lead to new methods for identifying those most at risk for caries, such as genetic tests that dentists could administer chairside.

Dr. Bretz noted that his twin research model also could be used to study the development of other diseases.

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