Genetical Research Of A Family With Nonsyndromic Congenital Tooth Agenesis And Eight Families With Ectodermal Dysplasia Syndrome

Background:Tooth agenesis is a common human anomaly that affects approximately2.6%-11.3%of the population. Tooth agenesis has sometimes been divided into2types:oligodontia, defined as agenesis of6or more permanent teeth, and hypodontia, defined as agenesis of less than6teeth. The number in both cases does not include absence of third molars (wisdom teeth). Tooth agenesis been also divided into nonsyndromic tooth agenesis which without associated systemic disorders and syndromic tooth agenesis which with associated systemic disorders. It was definite that MSX1and PAX9gene were associated with nonsyndromic tooth agenesis, and the most distinguishing feature of MSX1-associated tooth agenesis is the frequent absence of maxillary first premolars, whereas the most distinguishing feature of PAX9-associated tooth agenesis is the frequent absence of maxillary and mandibular second molars.There was report that the mutation of AXIN2gene could lead to tooth agenesis and colonic neoplasms. However the detection rate of MSX1and PAX9gene in patients with nonsyndromic tooth agenesis were lower, wich prompt that the genetic heterogeneity of nonsyndromic tooth agenesis is high, and there were new genes need to found out. The pathomechanism about MSX1and PAX9gene were not clear too.Hypohidrotic ectodermal dysplasia is a common syndrome that results in oligodontia. The patient had a characteristic facies, with frontal bossing,'saddle'nose, prominent lips. Hair was fine, dry, brittle, and sparse, and skin was thin, glossy, smooth, and dry, sweat glands dysplasia and congenital, sebaceous glands dysplasia and congenital, dysplasia and congenital. More than95pecent of the congenital ectodermal dysplasia is the X-linked recessive form which is caused by mutation of EDA gene.Nonsyndromic oligodontia and hypohidrotic ectodermal dyslasia may defect the patients masticatory function, appearance, physical development and psychological health, life quality, and even the life. In addition to the symptomatic treatment, such as dental reshaping and wear denture, the important intervention is to prevent the born of defected foetus by genetic and prenatal diagnostic.Objective:In this research, we aimed at collecting families with nonsyndromic oligodontia or hypohidrotic ectodermal dyslasia, and found out novel mutations of known genes or novel genes by using genetic techniques and molecular biological techniques, and rich the genetical theory about tooth' disorder. At the same time, provide informative genetic counseling to the patients and perform genetic and prenatal diagnosis to the pregnant women who want to prevent the defected fetus.Methods:A autosomal dominant nonsyndromic tooth agenesis family with four generation patients (11patients and12normal individual) was obtained. The medical history was taking carefully from family and followed the physical examination and oral cavity examination. Oral radiographic inspection was performed for some patients. Genomic DNA and cDNA were prepared from peripheral blood leukocytes of the family member. All coding regions and the intron/exon boundaries of MSX1, PAX9and AXIN2were amplified by polymerase chain reaction (PCR), and the PCR products were directly sequenced. Cosegregate analysis about the mutation and the disorder was done by direct sequencing. RT-PCR was performed to investigate if the mutation affected the gene splicing site. In order to exclude the possibility that the detected gene variation might be a polymorphism, DNA samples from100healthy control individuals were investigated by direct sequencing. Linkage analysis was done by STR around the gene to investigate if the mutation was associated with the disease.Eight famlies with hypohidrotic ectodermal dyslasia were collected, and gDNA and cDNA were prepared from peripheral blood leukocytes of the family member. All coding regions and the intron/exon boundaries of EDA gene were amplified by polymerase chain reaction (PCR), and the PCR products were directly sequenced. Cosegregate analysis about the mutation and the disorder was done by direct sequencing. In order to exclude the possibility that the detected gene variation might be a polymorphism, DNA samples from100healthy control individuals were investigated by direct sequencing. Four prenatal diagnosis were performed by direct sequencing about the muation wich had found in the probands. The sex of fetus was tested by amplification of SRY gene.Results:Nonsyndromic tooth agenesis family:(1) A novel mutation c.469+5G>A of MSX1gene and two SNPs, c.717C>T and c.718G>C, were identified in the proband.(2) The MSX1gene mutation c.469+5G>A was found in all the patients of the family, but not the normal individuals.(3) The mutation c.469+5G>A was not found in100normal controls.(4) No abnormality was found by RT-PCR about the mutation c.469+5G>A.(5) The maximum2-point lod scores of3.53was found on marker D4S2285, and the2-point lod scores of D4S3023and D4S2925were3.49and2.97respectively.Hypohidrotic ectodermal dysplasia families:(1) All the patients were found the mutation of EDA gene, C.466C>T (family1), c.871G>A (family2),467G>A (family3), c.663₆97del (family4), c.924+2T>A and c.1001G>A (family5), c.86₁01del (family6), c.467G>A (family7), c.878T>G (family8). Four mutation (c.466C>T,871G>A,467G>A, c.1001G>A) had be reported before, and four (c.663₆97del, c.924+2T>A, c.86₁01del, c.878T>G) were identified at first time in our reseach.(2) The novel mutations c.924+2T>A and c.878T>G were not found in100normal controls.(3) In famly8, the mutation c.878T>G was found in two male patients and females who had bore male patients, and not found in a normal male.(4) The EDA gene c.466C>T heterozygosis mutation was found in the fetus of family1, and the SRY gene was negative; The EDA gene of the fetus of family2was normal, and the SRY gene was negative; The EDA gene of the fetus of family3was normal, and the SRY gene was positive; The EDA gene of the fetus of family4was normal, and the SRY gene was positive. Conclusion:(1) The MSX1gene was the causing gene of the nonsyndromic tooth agenesis family.(2) We identified a novel mutation c.469+5G>A of MSX1gene, and expand the mutational spectrum.(3) By the association analysis about the genotype and phenotype, we found that nonsyndromic tooth agenesis caused by the mutation of MSX1gene has a high phenotype heterology, the patients may be hypodontia or oligodontia, and even in the same family the number of tooth agenesis of patients is different.The mutation c.469+5G>A of MSX1mostly affect second molars, followed by first and second premolars.(4) In this reseach we identified4novel mutation of EDA gene, and expand the number of reported mutation of EDA gene.