Genetic study of families affected with aggressive periodontitis.

Periodontitis is a multifactorial disease associated with several risk and susceptibility factors (66). Risk factors are part of the causal chain, or expose the host to the causal chain. The presence of a risk factor directly increases the probability of a disease occurring, and the absence of a risk factor reduces this possibility. Risk factors are modifiable. Contrary to modifiable risk factors, susceptibility factors often refer to nonmodifiable determinants or background factors, such as age, gender and genetic make-up. It is now evident that genetics form an important aspect in most diseases, including periodontitis. Elucidation of the genetic basis of periodontitis should permit a better understanding of disease etiology, allowing improved classification, diagnosis and treatment of periodontal diseases. Aggressive periodontitis (formerly termed earlyonset periodontitis, subdivided into prepubertal periodontitis, juvenile periodontitis and rapidly progressive periodontitis) is a group of infrequent types of periodontitis, characterized by early age of onset and rapid destruction of the tooth-supporting tissues in otherwise healthy individuals (5, 51). In patients with aggressive periodontitis, exposure to local irritants usually cannot account for the marked alveolar destruction, suggesting that host factors are involved in determining susceptibility to the disease. Although a variety of factors, such as microbial, environmental and behavioral factors, and systemic disease, are suggested to influence the risk of aggressive periodontitis, an individual s genetic make-up is a crucial factor influencing their systemic or host responserelated risk (42, 55). It is commonly believed that family studies remain the best approach for studying possible genetic causes of aggressive periodontitis. Therefore, this review focuses on family studies of aggressive periodontitis and the utility of genetic analytical methods in periodontology.