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

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ABSTRACT

Aim

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.

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.

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