Twin half-sibs: a research design for genetic epidemiology of common dental disorders.

Dental caries and the chronic type of periodontal disease are classic examples of common familial diseases that are complex and multifactorial in etiology. Due to previous methodological limitations, there is no information at present on the genetic and shared environmental risks within families that account for familial aggregation of these diseases. Such information, however, is needed in the long run to help specify modifiable family environments that affect the frequency and/or severity of the disease, and thereby to aid in the planning of prevention strategies to be targeted at the family level. Recently, an innovative genetic model has been described to test the genetic and environmental basis of chronic familial diseases in identical (monozygotic) twins, their spouses, and their offspring, who are genetically half-sibs. In this paper, the method is detailed and shown to be appropriate not only for partitioning shared genetic and environmental risks within families, but also for delineating maternal effects and assortative mating as two non-genetic mechanisms that may ultimately be found to affect the incidence of disease.