A Unique Form of Hypodontia Observed in Vietnamese Patients: Clinical and Molecular Analysis

Experimental and animal studies have revealed that several genes control the development of dentition. Mutations in MSX1 and PAX9 have been associated with dominantly inherited forms of human tooth agenesis that primarily involve posterior teeth. However, several individuals with this classic pattern of posterior tooth agenesis also lacked mandibular incisors. While mandibular incisor agenesis occurs rarely in the Caucasian population (approx. 0.08%), it has been shown to occur in as much as 2% of certain Asian populations. Objective: Based on previous studies which identified mutations in two genes, MSX1 and PAX9, we sought to determine if mutations in the coding regions of these genes are also responsible for this unique form of hypodontia. Methods: 500 sequential dental records were reviewed from consenting dental offices with a predominantly Vietnamese patient pool. A pedigree analysis was performed for six families, and DNA subsequently extracted from whole blood for both affected and unaffected members from three available families. Mutational analysis using direct sequencing of PCR products was performed to examine the coding regions of MSX1 and PAX9. Results: Our results confirm that mandibular incisor hypodontia is an inherited trait, and suggests an autosomal dominant mode of inheritance with incomplete penetrance. Sequence analysis confirmed the absence of any mutations in the coding regions of MSX1 or PAX9. Conclusion: Our preliminary analysis suggests that mandibular incisor hypodontia in the Vietnamese families studied is due to a gene other than MSX1 or PAX9. However, we cannot completely rule out that mutations in the intronic or regulatory regions of MSX1 or PAX9 may cause this phenotype. [Supported by the NIDCR T35DE07252-09 (EL), AAOF (SF-B), UT-HSC (SF-B), UCRC M01RR02558 (D.M.M), and R01DE13668 (RDS and SF-B)].