GENETIC SEGREGATION ANALYSES OF SERUM IGC2 LEVELS

The aim of this study was to determine whether there was evidence for a genetic component in the immune response as measured by IgG2 levels. The study was motivated by our studies of early-onset periodontitis ( EOP), a group of disorders characterized by rapid destruction of the s upporting tissues of the teeth in otherwise healthy individuals. EOP h as two subforms, localized juvenile periodontitis (LJP) and a generali zed form (G-EOP). IgG2 Levels are elevated in LJP but not G-EOP indivi duals; and African-American IgG2 levels are higher than Caucasian leve ls regardless of EOP status. IgG2 levels were determined in 123 EOP fa milies and in 508 unrelated non-EOP control individuals. Segregation a nalysis under the regressive model approach of Bonney was used to anal yze IgG2 levels for evidence of major locus segregation. After adjusti ng for LJP status, race, sex, and age, the best-fitting model was an a utosomal codominant major locus model (accounting for similar to 62% o f the variance in IgG2), plus residual parent/offspring and spousal co rrelations. Smoking and GM23 are also known to affect IgG2 levels. If additional adjustments are made for smoking and GM23, the best-fitting model is still a codominant major Locus but with no significant resid ual correlations.