| Hypoplasia of teeth root (HTR) disease is a disorder with physiological development of teeth root. According to clinical manifestation, it was classified into many subgroup: Dentinogenesis defect of root; cementinogenesis defect of root; shape anomaly; defect of teeth root attachment organ and so on.. It was reported that HTR could occur with an incidence of 1-10% in deciduous and permanent dentition, which resulted in non-root or short root. HTR could affect not only normal dentition function but also appearance of face, which brings severe harms to physiological and psychological activities. So it was a interested topic for stomatological workers. However up to now, the causative genes of HTR weren't reported, and the mechanism of teeth root formation were unknown. It needed further research if it existed specific genes initiating root development. So Aims of my research is to screen and clone causative genes of HTR. Firstly patients with 3 kind of HTR phenotype were collected to screen candidate gene by clinic, laboratory, pathologic examination, then by fuctional cloning strategy of molecular genetic research. Furtherly candidate genes were inspected to find mutation sites for identifying genetic change of genes. Then from differentially expressed auxo-genes libarary between HTR children and normal control children causative genes were defined by subtractive cloning method, finally which are studied to explore molecular mechanism regulatingteeth root formation by location of timing and tissue expessing, moreover celltransfection of Eukaryotic expression vector. So it is wished to clarify molecular genetic backgroud of HTR disease, and provide new theory about molecular mechanism of teeth root biological development, and obtain practicable and theoretical results for clinical diagnosis, therapeutics and prevention of HTR disease. The following experiments were carried out.Section one : The inspection and analysis of HTR patients In this experiment, three children with various HTR phenotype were inspected clinically and by laboratory test, then their shedding teeth were examined by pathologic test. Finally abnormal results were found to diagnose the entity of disease, furthermore to pick up the suspected candidate gene by functional clone strategy. The results of clinic and laboratory test were analyzed to show that 3 kind of HTR diseases are probably the inherited disease with mutated gene or the dysplasia disease. They were separately and preliminarily assessed as a novel hypophosphatasia with HTR phenotype, a typical children hypophosphatasia, a novel syndrome (including Dentinogenesis imperfecta DGI, hypohidrotic ectodermal dysplasia HED, HTR). Pathologic test of patient one showed that teeth crown grew well but without teeth root structure, with sub-mineralized dentin, resorption, and abnormal dentin stacking in apical area, so it was HTR. Pathologic test of patient two showed that pulp chamber and root canal enlarged as "shell or bubble"structure, cementin disappeared with sub-mineralized dentin, incremental line were increasing, Caliber and arrangement of dentinal tubule weren't average. So it was diagnosed as odontophosphatasia. Pathologic test of patient three showed that enamel-dentinal junction teeth arranged as line structure with broad interspace, dentin formed in a great mess, and pulp chamber was filled without root structure. So it was diagnosed as a complexsyndrome.Section two : Mutation screening of candidate genes for HTR patientBased on the results of section one, ALPL and EDA gene were picked up as candidate genes for HTR patient by functional clone strategy. Gene mutation were screened by PCR-SSCP technique and gene sequencing. Results of Patient one showed that Exon5 of ALPL gene were abnormal by electrophoresis methods, then sequencing revealed a G--A transition of 583rd site and heterozygote structure. Codon CCU-GCU was predicted to result in a substitution of Arginine by Histidine at 136th ammo acid. Mutation type was 583G>A, R136H. Results of Patient two revealed a C-G...
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