The molecular biological analysis of autosomal amelogenesis imperfecta, and the gene diagnosis.

牙釉质发育异常是一组影响釉质形成的遗传性疾病，其特征在于临床和遗传异质性。遗传学上分为两种类型，X连锁型和常染色体型。到目前为止，已发现编码釉蛋白、激肽4、釉蛋白溶素和DLX3的基因突变导致常染色体釉质发生突变，并且它们可能比X连锁形式更普遍。此外，成釉蛋白是牙釉质中的细胞外基质蛋白质之一，并且被认为是负责常染色体成釉细胞生成的原因，因为成釉蛋白缺失小鼠的测试发展了严重的釉质发育不全。因此，成釉蛋白基因也被认为是一个候选人负责常染色体釉质发生的突变。我们采用单链构象多态性（SSCP）分析和DNA测序研究了4例日本患者的成釉蛋白、釉蛋白和溶釉蛋白基因。在成釉蛋白基因的翻译区发现了一个单核苷酸取代和一个三核苷酸缺失。然而，核苷酸取代并不导致编码的氨基酸残基的改变，这意味着它是氨基酸残基的同义取代。三核苷酸缺失是一种基因多态性，至少在日本人中对人类牙齿的表型没有影响，正如我们在以前的资助“科学研究（B）第15390633号”中报道的那样。随后，我们将注意力集中在患者的成釉蛋白基因的启动子区域。结果，来自患者的PCR（聚合酶链式反应）扩增产物由两种产物组成，其中一种显示出预期的较小尺寸。提示患者的成釉蛋白基因启动子区可能存在一个等位基因缺失。

Amelogenesis imperfecta is a group of inherited disorders affecting enamel formation that are characterized by clinical and genetic heterogeneity. It is genetically classified into two forms, X-linked type caused by the mutated amelogenin gene and autosomal type. So far, mutations of the gene encoding enamelin, kalliklein 4, enamelysin and DLX3 were found to cause autosomal amelogenesis imperfecta, and they are likely to be much more prevalent than X-linked form. Furthermore, ameloblastin is one of the extracellular matrix proteins in tooth enamel and thought to be responsible for autosomal amelogenesis imperfecta since tests of ameloblastin-null mice developed severe enamel hypoplasia. Hence, the ameloblastin gene is also considered to be a candidate responsible for autosomal amelogenesis imperfecta. We investigated the ameloblastin, enamelin and enamelysin genes of 4 Japanese patients using single-strand conformational polymorphism (SSCP) analysis and DNA sequencing. One single nucleotide substitution and a trinucleotide deletion were identified in the translated region of the ameloblastin gene. However, the nucleotide substitution does not result in the change of the encoded amino acid residue, which means it is a synonymous substitution of amino acid residue. The trinucleotide deletion is a gene polymorphism that has no effect on the phenotype of human tooth at least in Japanese as we reported in the previous grant 'Scientific Research (B) no.15390633'. Subsequently, we focused our attention on the promoter regions of ameloblastin gene of the patients. As a consequence, the amplification product by PCR (polymerase chain reaction) derived from a patient was composed of two products and one of which showed the smaller size the expected. It indicates that one of the allelic genes might have a deletion in the promoter region of the amelobnlastin gene of the patient.