Clinical And Molecular Genetic Studies In A Chinese Family With Nonsyndromic Oligodontia

Background Tooth agenesis is a common anomaly that affects approximately 1.6%～20% of the population and can occur with a nonsyndromic trait or as part of clinical manifestations in a genetic syndrome. According to the number of teeth absent, the defects have been classified into three types as follows: Hypodontia (MIM 106600) is defined as an absence of one to six permanent teeth (the third molars are excluded). Oligodontia (MIM 604625) or congenitally lack of more than six teeth is at a lower frequency, which affects approximately 0.08～1.1% of individuals in the general population. Anodontia is used to describe the congenital absence of all the teeth. It has been proposed that both genetic and environmental factors are responsible for tooth agenesis. The inheritance mode is an autosomal-dominant, recessive-dominant or X-linked and the sporadic form has been also described. Thus far, MSX1 and PAX9, which encode for transcription factors, are considered to be two candidate genes associated with syndromic and non-syndromic tooth agenesis, non-syndromic oligodontia, respectively. In humans, the first MSX1 mutation was identified by Vastardis et al, which co-segregated with tooth agenesis in a family with autosomal-dominant manner. Since then, a total of nine mutations, including gross deletion, nonsense or frameshift mutations have been identified in families with hypodontia or oligodontia. Besides, sixteen mutations in PAX9 gene had been identified in the families with nonsyndromic oligodontia (http://www.hgmd.cf.ac.uk/ac/index.php). A comparative analysis of families bearing mutations suggested that specific genes were responsible for specific types of tooth agenesis. MSX1-associated oligodontia is characterized by the congenitally missing of the third molars and second premolars, whereas PAX9 mainly affects molars development. Asians, in particular Chinese, have a higher prevalence of oligodontia. However, the genetic basis of congenitally missing teeth is little known. Thus, it will be better understanding the pathogenetic mechanism of oligodontia and genotype/phenotype correlations to study more pedigrees.Objective This study aims to explore the feature of phenotype and to detect the mutation of MSX1 and PAX9 genes in a four-generation Chinese family with nonsyndromic oligodontia.Designs Detailed history and pedigree information were confirmed by using a questionnaire. Moreover, clinical manifestations and panoramic views of the patients were recorded by taking careful physical and oral examinations. Then a pedigree was constructed by extended interviews in the family with nonsyndromic oligodontia. The clinical feature and inheritance mode were concluded by studying the data. After informed written consents were obtained, blood samples were collected from seven affected and seven unaffected family members. Another 100 unrelated healthy individuals from volunteers were taken as controls and human genomic DNA of all samples were isolated from the whole blood. Furthermore, all exons and flanking intronic boundaries of the MSX1 and PAX9 genes were amplified from genomic DNA by using polymerase chain reaction and then sequenced in both forward and reverse directions. Meanwhile, the websites of CBM, pubmed and bioinformatic were used to verify the mutation and evaluate its functional effect, respectively.Results The majority of clinical manifestations were the agenesis of the third molars and second premolars, which were inherited in an autosomal-dominant mode with high penetrance. In addition, it was noteworthy that some other dental anomalies, such as a transformed morphology and a transposition of teeth, as well as a large number of teeth missing were all found in our family. Sequence analysis revealed a G to A base substitution in MSX1 and no PAX9 mutation was identified. This heterozygous mutation IVS1-2A>G, which was located in the receptor splice site of MSX1 and made the highly conserved consensus sequence change from AG to GG. The results demonstrated the presence of the mutation in all affected family members but not in unaffected individuals or 100 unrelated healthy controls. In addition, the functional effect of the mutation was evaluated through the bioinformatic website online. The results predicted that the mutation leaded to the loss of the normal splice site and the activation of a potential new splice site created by the mutation. It suggested that the mutation IVS1-2A>G might disturb the splicing machinery to process the intron1 acceptor splice site properly. Moreover, the loss of function which was produced by the mutation might be the underlying genetic basis for nonsyndromic oligodontia.Conclusions As far as we know, this is a novel splicing mutation identified in the MSX1 gene. Our finding suggests that it might be responsible for nonsyndromic oligodontia in this family. Moreover, MSX1-associated oligodontia is characterized by the congenitally missing of the third molars and second premolars with an autosomal dominant mode. Our results provided further evidence to understand the pathogenetic mechanism of oligodontia.