Genetic factors associated to the etiology of class III malocclusion in a Colombian population group.

1. Segregation Analysis of class III malocclusion in Colombian families: The goal of this study was to evaluate specific genetic transmission models of mandibular prognathism in a series of Colombian families. Materials and Methods Sample: 32 families with a history of mandibular prognathism from a population of different regions of the Colombia. The control group included unaffected members of the family and unrelated individuals with out class III malocclusion. In this study were identified 32 probands with class III malocclusion and mandibular prognathism from the orthodontics clinics at Javeriana University and several orthodontic clinics in Bogotá and Bucaramanga (cities of Colombia). Complete pedigrees for all families were taken and the affected status of relatives in each family was confirmed by dental chart, cephalometric, facial and dental photos, and/or dental models. Subjects who had syndromes, pathologies such as clef/lip palate, or general physical disease were excluded from the study. The study protocol was approved by Pontificia Universidad Javeriana ethical committee, and informed consent was obtained from all subjects. The pedigrees of 32 families comprised of 810 individuals (32 probands, 441 first-degree relatives, 239 extended relatives, and 98 individuals related to the proband through marriage). Consanguinity was present in two of these families (107 first-degree relatives, 69 extended relatives, and 51 individuals related to the proband through marriage). Assessment: The probands were selected from patients referred for orthodontic treatment. A confirmed negative ANB angle will be a prerequisite for enrollment the proband. The linear and angular values were measured and compared in lateral radiographies through Mc Namara, Steiner and Legan¿s cephalograms. All probands had a lateral cephalometric radiograph, facial and dental photos, dental models and dental chart. Class III malocclusion in the relatives (on whom radiographic records were not available) was determined by the presence of an edge-to edge incisor relationship, anterior crossbite, concave facial profile and orthodontics clinical history. In this way were evaluated 291 individuals and the condition of the other relatives that could not be evaluated were confirmed by pictures. Age of the affected at the time of diagnosis ranged from 6 to 70 years old. To clarify the impact of environmental factors on mandibular prognathism, we gave a questionnaire to subjects to ask about habits and pathologies that can be associated with this malocclusion. The questions included history of trauma, habits, diseases and instrument deliveries. All answers were confirmed in a careful interview. Statistical methods: Segregation analysis is a statistical method for determining the mode of inheritance of a particular phenotype from family data, particularly with the aim of elucidating single gene effects or so-called major genes. We established the Hardy-Weinberg equilibrium in the sample and then we tested an analysis model for statistical detection of major transmissible effects in a dichotomous trait, but with this model we could not test multigenic or multifactorial contributions to the trait. Results: Four models were evaluated (Dominant, co-dominant, additive and recessive). These models assume that variation in a trait among individuals, results from a major gene effect and residual variation which may reflect both familial correlations and individual variation.