Peutz-Jeghers综合征脆性组氨酸三连体基因突变与癌变的关系

背景与目的：Peutz-Jeghers综合征（Peutz-Jeghers syndrome,PJS）是一种常染色体显性遗传性疾病。脆性组氨酸三连体(fragile histidine triad,FHIT)基因是定位于3p14.2脆性位点区域的重要抑癌基因。我们以往的研究结果认为PJS患者在3p14.2区域可能存在易感基因。本文旨在明确PJS患者FHIT基因突变与癌变的关系和FHIT基因的改变及规律。方法：应用变性高效液相色谱（DHPLC）分析、聚合酶链反应-单链构象多肽分析技术（PCR-SSCP）和DNA测序方法,对6个PJS家系中的15个患者及其20例正常家族成员的FHIT基因进行了研究。结果：在6个家系中,有1位患者的FHIT基因第159位核苷酸由G→T,相应的第54位密码子编码的氨基酸由谷氨酸变成终止密码子;在第62位密码子处存在碱基G插入,使读码框架发生移位,在第111位密码子处提前出现终止密码子;在2例癌变患者的息肉标本DNA和癌标本DNA中检测到FHIT基因第8外显子的纯合性缺失;在3个散发的PJS患者中发现,患者与其母亲在第8外显子,有相同的SSCP带型和DHPLC峰型,DNA测序结果显示,在第98位密码子处发生同义突变,由CAT→CAC,相应编码的氨基酸未发生改变,均为苏氨酸。另外,有7例患者和2例正常人在FHIT基因的第6内含子5′端第42位核苷酸位点发生由A→G的点突变。结论：FHIT基因在PJS患者中存在点突变,突变频率较低,在癌组织中存在缺失,这提示FHIT基因突变可能参与了PJS发病过程,而FHIT基因缺失可能与癌变有关。

Mutations of fragile histidine triad gene in Peutz-Jeghers syndrome and canceration

BACKGROUND & OBJECTIVE: Peutz-Jeghers syndrome (PJS) is an autosomal dominantly inherited disease. Fragile histidine triad (FHIT) gene is an important tumor suppressor gene at the fragile sites region of 3p14. The authors' previous study suggested that PJS patients might have a susceptible gene at the region of 3p14.2. This study was designed to reveal the relationship between the variant of FHIT gene in PJS and its canceration. METHOD: Mutations of FHIT gene in 15 PJS patients and 20 unaffected members in 6 PJS families were determined using denaturing high-performance liquid chromatography (DHPLC), polymerase chain reaction-single strand conformation polymorphism(PCR-SSCP) and DNA sequencing techniques. RESULTS: A non-sense mutation and a frame-shift mutation were identified at codon 54(GAA to TAA) (exon 6) which led to the change of the amino acid from glutamic acid (Glu) to stop codon, and a guanine insertion at codon 62 in exon 6 resulting in a premature stop codon TGA at codon 111 in one PJS patient. A homozygous deletion and a synonymous mutation were detected in exon 8. The homozygous deletion of exon 8 in FHIT gene was found in two polyps tissues and two cancerous tissues. And in 3 sporadic cases, the patients and their mothers have the same bands of SSCP and the same elution profiles of DHPLC when exon 8 was amplified. The DNA sequencing result showed that a synonymous mutation (polymorphism) occurred at codon 98 [CAT (H)-->CAC (H)], this mutation resulted in no change of amino acid. In addition, one base substitute from A to G mutation at 5'end, +42 nucleotide in intron 6 of FHIT gene was detected in seven patients and two unaffected members. CONCLUSION: PJS patients have low frequency point mutation of FHIT gene and their cancerous tissues had homozygous deletions in FHIT gene. This study indicated that the mutations and deletions of FHIT gene in PJS may play a role in the development of PJS and their cancerations.