Clinical And Related Basic Research For Hereditary Dentinogenesis Imperfecta

Hereditary dentinogenesis imperfecta is a common genetic disease for human beings.The abnormalities usually locate in mesoderm or the dental papilla with a prevalence ofabout1/10000-1/60000. Shields divided the hypoplasia of dentin into two types:dentinogenesis with3subtypes and dentin dysplasia with2subtypes. This study mainlyfocused on the dentinogenesis imperfecta type II (DGI-II) and dentin dysplasia type I(DD-I).DGI-II, also called as hereditary opalescent dentin, is an autosomal dominant geneticdisease with a100%penetrance and a1/6000-1/8000prevalence. It could be observedboth in primary dentition and permanent dentition with no gender difference. DGIpatients generally exhibit a dental developmental disorder without any systematic diseasesuch as skeletal dysplasia. The dental disorder is usually noted as an amber oryellowish-brown small crown with exfoliate enamel in addition with severs abrasion.DD-I is also an autosomal dominant genetic disease; its prevalence is1/100000whilepenetrance is less than100%. No obvious tooth morphology or crown colour changes could be observed except short crown and shadow image in X-ray radiograph might bedetected without any caries,and other unkown causes.In2001Zhang et al found that it is DSPP gene that caused DGI-II. Although no articlewas published on the relationship between DSPP and DD-I, DSPP is still a criticalcandidate gene for DD-I. Up till now more than20mutant sites have been reported inDSPP and the mutant sites vary between different nationalities, different families anddifferent peoples. However some families which suffered from the disease reported nomutant site. In this study we carried out clinical and related basic research in two DGI-IIand one DD-I families in western China aiming to find their disease-cause mutant sites,so as to made clear clinical diagnosis and provided possible molecular diagnosis for thetwo diseases.Part1: Clinical and Family Study on Hereditary DGIWe collected two patients diagnosed as opalescent dentin and one patient diagnosed asdentin dysplasia in clinical work. General information was obtained through historycollection, oral examination, physical check-up and family study. What was more wetook panoramic tomography, lateral cephalograms, sternum and spinal radiographs forthe three patients and made Routine Blood Test for them. Results：The anterior teeth ofpatient1both in the maxillary and mandible dentition could be observed as amberchanges and some partial defects happened in dental tissues. Patient suffered fromanterior cross bite exhibiting subside in the middle third of the face with a family history.The X-ray radiograph indicated pulp cavity atresia and short teeth roots；Patient2suffered from severe abrasion in primary dentition with short crowns in yellowish-browncolour. Some of the anterior primary teeth are detained and he had a family history forDGI-II; the X-ray indicated that all the primary teeth had atresia pulp cavities and shortroots. The patient3except flushing in both cheeks, no abnormalities could be detected inteeth considering colour and morphology, this patient had a family history for DD-I.TheX-ray indicated that there existed unknown cause shadow in periapical area without anycaries. Conclusion: The first two patients had typical clinical symptoms for DGI-II andthe X-ray and family study are in accordance with the diagnosis for autosomal dominant genetic disease. Patient1was also suffered from cross bite in anterior teeth; as a result,she was diagnosed as DGI-II with Angle III malocclusion. The clinical symptoms, X-rayexaminations and family study of patients3were also in accordance with the diagnosisof DD-I. This part of the study made basic clinical study for the three patients andprovide some clinical basis for further research.Part2: Related Basic Research for Hereditary Dentinogenesis ImperfectaStudy1: Detection of the mutant site in DSPP for patients diagnosed as hereditarydentinogenesis imperfectaWe collected3mL peripheral blood from each patient and their parents and thenextracted DNA from the blood samples. Primers for the DSPP gene were designed basedon literature and Genebank data base. Exons of DSPP were amplified through PCR andthe product was purified. Then samples were taken DNA sequencing and sequentialanalysis was made combined with DSPP gDNA. Results: We had confirmed that patient1had frame shift mutation which was led by base deletion included12bases throughgene sequential analysis and the whole three families had4SNP sites. Conclusions：Frame shift mutation which was led by base deletion in DSPP gene for patient1furtherconfirmed his DGI-II diagnosis. This result provided some theoretical basis for furtherstudy of our research work in the relationship between DSPP and DGI-II. We had notfound any gene abnormalities for patient2and we thought that it might be associate withother genetic factors, thus further study was still needed. The same with patient2, wehadn’t found DSPP gene mutation related clinical symptoms in patient3; however othercandidate gene in the possible mutant region which might cause this disease should betaken into consideration such as DMP1.Study2: Ultrastructural Research on Dentin from Hereditary DentinogenesisImperfecta PatientThe two detained anterior teeth were collected from patient2and that from a normalcontrol with the same age and gender. The four teeth were divided into two groups. Onegroup was polished and then acid etched after cleaning. Finally metal sprayed whendesiccated. Scanning electron microscope was used to observe the surface structure of the dentin. The other piece was cut into small pieces in length way, after polishing thesamples were dehydrated and fixed. Dentin slice sections were surveyed under lightmicroscope.Results: The dentin tubes were observed orderly arranged with regularmorphology. Enamel-dentine junction in normal control group was in an undulantwavelike form. However dentin tubes in patient were arranged disorderly with partiallyinterlocked,or became narrower,or even disappeared. Some area of the dentin from thepatient had no dentin tube existed and the junction between enamel and dentin was in alinear filiform. Conclusions: Compared with normal healthy person, patients of DGI-IIhad disorderly arranged dentin tubes with partially interlocked. And the number of themwas decreased with smaller diameter. The junction between enamel and dentine lackedserrated interleaving.