Periodontitis In Adults
Clinicians have long suspected that susceptibility to periodontitis differs among racial and ethnic groups. In the U.S. African-Americans have more severe disease than Caucasians. "s Elsewhere, Sri Tankans and South Pacific islanders appear to be more prone to disease than other groups with similar environments.' Although these differences may be clue to unrecognized environmental factors, they also may be the result of differences in genetic makeup.
Measures of periodontitis and gingivitis are correlated within families.""1 The basis of this similarity—whether it be shared environmental factors or genes— has been investigated in several large family studies. Initially, studies of Japanese and Hawaiian c hildren suggested that gingivitis was due to recessive genes.*4 Later, correlations within families (e.g., sibling, parent-offspring) were used to estimate genetic and environmental variances lor periodontitis among various racial groups in Hawaii. It was concluded that similarities within families were attributable to cultural inheritance and the common family environment, but not shared genes.1 1 Beat\ et al" reported similar results in a sample primarily ol \frican-Americans. The correlations in clinical periodontal measures were greater between mothers and offspring than between fathers and offspring. Sibling correlations in this study were generally low, and the hypothesis of no familial correlation (and hence no genetic effect) could tiol be rejected.
Twin Studies of Adult Periodontitis
As early as 1940, Novack"" recognized that the periodontal conditions of identical twins were often similar. Independent twin studies in Minnesota and Virginia concluded that «i significant heritable component to adult periodontitis exists. The Minnesota group'*" studied both reared-together and rcarcd-apart adult twins. Uxainples of twins in this study are depicted in Color Figs. KM and 10-4. Between 38% and 82% ot the population variance for gingivitis, probing depth, and clinical attachment loss could be attributed to genetic variation. A significant heritable influence on radiographic crestal alveolar bone height was found in these same twins. Moreover, reared-apart VI/. twins were no less similar than reared-together MX twins, indicating that the family environment had no significant influence on clinical measures of disease. The latter finding was surprising because it is within this environment that oral hygiene behaviors are learned and pathogenic bacteria may be acquired from other family members.
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