Phenotypic assessment of early onset periodontitis in sibships.

Early onset periodontitis is a group of familial diseases that are not yet clearly defined by etiologic mechanisms, although some risk factors have been recognized. The disorders include a localized form of juvenile periodontitis (JP), and a more generalized form (GP). In a family study, 39 sibships (116 individuals, aged 13-48) were evaluated for clinical indices, neutrophil chemotaxis, and serum antibodies to A. actinomycetemcomitans (Aa). Of 77 siblings, 41 were healthy at examination. In 14 sibships, all affected persons had JP; 14 other sibships had all affected individuals with GP; and 11 had at least one sib with each form. For probands with decreased chemotaxis, 71% of affected sibs and 36% of clinically healthy sibs had decreased chemotaxis. For Aa seropositive probands, 83% of affected siblings and 65% of currently healthy sibs were also seropositive. The associations of disease with these risk factors were stronger in JP-only sibships. Some affected sibs had neither risk factor, while many currently healthy sibs had 1 or both. While these 2 factors demonstrate population association with disease, neither fits the pattern expected within families to clearly suggest a causal mechanism. The assessment of within and among family variability remains the best approach for recognition of possible causal mechanisms and sources of heterogeneity.