Methods: 32 probands with mandibular prognathism were identified. Complete family histories for each proband were taken, and the affected status of other individuals in each family were confirmed by cephalometric, photographic, and/or dental models. Subjects who had pathologies or syndromes were also excluded from the study. The study protocol was approved by the Pontificia Universidad Javeriana, and informed consent was obtained from all subjects. The study sample of 32 families comprised of 810 individuals. For our analyses, we assumed the distribution of the three genotypes (TT, TC, CC) in the population to be in Hardy-Weinberg equilibrium. According to the Likelihood Ratio Criterion four models were evaluated for segregation analyses: dominant, recessive, additive and co-dominant major gene models. These models were compared in the 30 families without consanguinity and in the two large families with consanguinity.
Results: The Odd Ratio analysis in the 30 families without consanguinity showed that the risk to have class III malocclusion increase in the recessive model (OR= 3,49). In contrast a dominant major gene model provided the best fit to our class III malocclusion pedigrees in the families with consanguinity (OR= 7,39).
Conclusion: These findings suggest that the inheritance model in class III malocclusion depend on the presence of consanguinity in the families. (Supported by ICGEB grant CRP/COL04-03).