本篇論文的主要目的是為了解臨床上具有Modini氏畸型(Modini’s dysplasia)及前庭導管擴大(Enlarged vestibular Aqueduct)之聽障患者PDS基因正常與否。本研究對象為10位臨床上具有前庭導管擴大及耳蝸發育不全的非症候群語言學習前感音神經性聽障兒童及50位聽力正常人。在正常人中，以SSCP的方法快速進行PDS基因的篩檢並無發現異常或PDS基因多型性。分析10位患者，我們以PCR方法及逐一定序分析PDS基因上21個exons，共發現三個PDS基因的突變點。此三種PDS基因突變分別為IVS 7 -2AG、IVS 16 -6GA及IVS 15 +5GA。為能更深入了解突變型是否為親代遺傳或是自發性突變，故收集5個具有IVS 7 -2AG突變之家族，針對PDS基因IVS 7 -2AG進行分析，對同型結合子突變型患者的雙親進行序列分析，均為IVS 7-2AG/wt異型接合子突變型。IVS 7 -2AG突變點是位於splice acceptor site，這個突變最可能影響PDS基因的剪接(splicing)改變，而得到不正常的RNA產物。由RT-PCR的結果顯示，IVS 7 -2AG突變會造成轉譯前mRNA剪接的錯誤，造成整段的Exon 8序列缺失，因而引起frameshift，並在第311個氨基酸位置形成停止密碼(stop codon)。實驗結果證明具有Modini氏畸型及前庭導管擴大之聽障患者的PDS基因皆有突變，可提供臨床上聽障患者的基因檢測指標。
The sensorineural disorder is the most common cause in severe hearing impairment, which affects about 1 in 1000 children and more than 50% of the disorder are thought to be inherited. Pendred syndrome is an autosomal recessive disorder characterized by congenital sensorineural hearing loss combined with goiter. The hearing loss is associated with temporal bone abnormalities ranging from isolated enlargement of the vestibular aqueduct (EVA) to Mondini dysplasia. The gene for Pendred syndrome (PDS) encodes a chloride- iodide transport protein of 780 amino acids named "pendrin". Mutations of this gene are also responsible for nonsyndromic autosomal recessive hearing impairment (DFNB4). To evaluate the relationship between prelingual deaf patients with EVA and Mondini dysplasia and PDS gene mutation, we analyzed 10 prelingual deaf patients associated with EVA and Mondini dysplasia. All of ten patients have PDS gene mutations. Of these ten mutations, seven are found to be homozygous for a splice acceptor site mutation that occurred at position IVS 7 -2AG, one heterozygous mutation for IVS 16 -6GA and two heterozygous for IVS 15 +5GA. We also performed family study on five probands with IVS 7 -2AG mutation. All were found to inherit the same mutant alleles from their parents. To determine the effect of this splice acceptor site mutation on patients'' PDS expression, total RNA extrated from transformed lymphoblastoid cell lines was reverse transcribed and amplified by polymerase chain reaction (RT-PCR). Sequencing of the RT-PCR products revealed that the transcripts from the allele with IVS 7 -2AG mutation skip exon 8 entirely, resulting in a joining of exons 7 and 9. Deletion of exon 8 resulted in frameshift and premature termination of translation. This study would support non-syndrome hearing loss associated with EVA and Mondini dysplasia might be caused by splice site mutation in the PDS gene.
