ABSTRACT

Mandibular prognathism (MP), defined as the difference in the size and relationship of maxilla and mandible, is the most serious anomaly in the practice of orthodontics. Incidence of MP varies among different populations; it is highest in Asian populations (15–23%) and lowest in Caucasian populations (0.48–4%). Genetic and environmental factors are suggested in the etiology of MP, but the contribution of these factors is not known. This study was designed to determine patients with MP in 3 generations of the families and to evaluate familial transmission of MP in Turkish families.

To reveal the effect of genetic factors on MP, we created pedigree charts for 99 subjects with severe skeletal Class III MP who planned to undergo or had undergone orthognathic surgery. Three generations of each patient's family was assessed on pedigree charts. The relatives of the probands were evaluated with photos and a detailed interview to confirm the prognathic phenotype.

The average ANB, SNA, and SNB angles in the probands were −2.65°, 79.92°, and 82.57°, respectively. A total of 1847 family members were examined, and 12.7% had MP. Men were slightly more affected than women. Most families (89%) had at least 1 member with MP other than the proband. The affected ratios of the first- and second-degree relatives were 20% and 7.3%, respectively. The affected ratio of fathers of probands (25.7%) was more than twice that of mothers of pronbands (9.9%), and siblings showed a 17.8% affected ratio.

A high frequency of MP was seen in families of patients with skeletal Class III, suggesting a genetic transmission.