Segregation analysis of mandibular prognathism in Korean orthognathic surgery patients and their families

Objective: To investigate the existence of genetic influences on the incidence of mandibular prognathism (MP) in Korean Class Ill patients. Materials and Methods: The probands consisted of 100 Class Ill patients with MP (51 men and 49 women; mean age, 22.1 +/- 5.2 years; SNA, 81.2 degrees +/- 3.2 degrees; SNB, 84.1 degrees +/- 3.9 degrees) who underwent orthognathic surgery. Using three-generation pedigree charts, questionnaires, and clinical examinations, general information and information regarding MP for a total of 3777 relatives of the probands (1911 men and 1866 women) was ascertained. Familial correlations of MP between possible pairs in the pedigree were estimated. Heritability (h(2)) of MP under various models was estimated. Segregation analysis was conducted under the assumption of the nonpolygenic multivariate logistic model and finite polygenic mixed model. One-, two-, and three-susceptibility-type models were evaluated. Results: Among 3777 relatives, 199 (97 men and 102 women) were affected with MP (5.3%). Correlation coefficients of MP incidence in full siblings and in parent-offspring were .2003 and .2036, respectively (all P < .001). The h(2) of MP was estimated as 21.5% after adjusting for sex and founder effects. Two- and three susceptibility-type models showed that the general model fit better than the other models. MP incidence did not have a major gene transmission model and was influenced by numerous minor effect genes and their additive effects. Conclusion: These results suggest that the inherited susceptibility to MP in Korean Class Ill patients might be due to the summation of minor effects from a variety of different genes and/or influence of environmental factors, rather than Mendelian transmission of major genes.