Genetic basis of non syndromic hypodontia: a DNA investigation performed on three couples of monozygotic twins about PAX9 mutation.

INTRODUCTION Hypodontia, agenesis of one or of more teeth, is a common developmental dental anomaly. To date, over 200 candidate genes have been demonstrated to be active in tooth development. The genes Pax9 plays an important role in the initial stage of odontogenesis. Mutations of Pax9 are associated with autosomal dominant forms of oligodontia, the agenesis of more than six teeth and occasionally of premolars (MIM 604625) in humans. The aim of the present study was to screen the candidate gene causing the non syndromic hypodontia, with agenesis of upper third molars and upper lateral incisors, in three couples of twins. MATERIALS AND METHODS Peripheral blood samples taken for routine laboratory investigations were used for genotyping. Total genomic DNA was extracted from the buffy coat of 1 ml of EDTA blood samples using phenol-chloroform and the salting out procedure. RESULTS The insC mutation (nt793, exon4) was observed in the sequencing results by the use of the primers hPAX9ex4F and hPAX9ex4R. InsC raises a frameshift mutation that introduces a nonsense codon so the mRNA activity results impaired. CONCLUSION In this work, it is described how the same mutation is responsible for a form of dental agenesis--less severe in the number of missing teeth--leading to hypodontia instead of oligodontia. Therefore, it is possible that mutations of the same gene cause different phenotypes; so we can presume that some modifier genes moderate the effect of the first mutation.