In this study, a novel frameshift mutation, the twenty-nucleotide deletion (c.128_147del20, p.Met43Serfsx125), in exon1 of MSX1 was detected in a Chinese family causing autosomal dominant nonsyndromic oligodontia.
The objective of the present study was to search for Msh homeobox 1 (MSX1), paired box gene 9 (PAX9), ectodysplasin‑A (EDA) and axis inhibition protein 2 (AXIN2) variants in a family with isolated oligodontia and analyse the pathogenesis of mutations that result in oligodontia phenotypes.
We identified two novel MSX1 variants with an amino acid substitution within the homeodomain; Thr174Ile (T174I) from a sporadic hypodontia case and Leu205Arg (L205R) from a familial oligodontia case.
DNA sequencing of the MSX1 gene revealed two mutations in the two patients with oligodontia: a heterozygotic silent mutation, c.348C>T (P.Gly116=), in exon 1 and a homozygotic deletion of 11 nucleotides (c.469+56delins GCCGGGTGGGG) in the intron.
Recently, several genes have been reported with mutations or variants that underlie a number of syndromic and non-syndromic forms of oligodontia including MSX1, PAX9, AXIN2, EDA and WNT10A.
Previous studies have indicated that mutations in the homeobox gene MSX1, paired domain transcription factor PAX9, and EDA are associated with non-syndromic oligodontia.
Oligodontia as well as hypodontia (lack of one or more permanent teeth) are highly heritable conditions associated with mutations in the AXIN2, MSX1, PAX9, EDA, and EDAR genes.
Multiple previous reports confirm that several missense alleles of MSX1 exhibit Mendelian inheritance of an oligodontia phenotype (agenesis of more than six secondary teeth besides third molars).
Therefore, the identified 11-nucleotide deletion may decrease the expression level of the MSX1 protein, but the link with oligodontia needs further study.
The occurrence of non-syndromic still remains poorly understood, but in recent years some cases have been reported where mutations or polymorphisms of PAX9 and MSX1 had been associated with non-syndromic oligodontia.
Considering the discrepancy between the high incidence rate of agenesis and the relatively small number of reported causative mutations in PAX9, MSX1 and AXIN2 genes, the genetic contribution to oligodontia probably is much more heterogeneous than expected so far.
The most distinguishing feature of MSX1-associated oligodontia is the frequent (75%) absence of maxillary first bicuspids, while the most distinguishing feature of PAX9-associated oligodontia is the frequent (> 80%) absence of the maxillary and mandibular second molars.
Our finding suggests that this transition might be the first described mutation of MSX1 that might be responsible for oligodontia and showing incomplete penetrance.