中国遗传性胰腺炎患者胰蛋白酶原基因多位点杂合突变及其临床特征

用基因产物直接测序法对2个遗传性胰腺炎家系中胰腺炎患者(共有4例成员)的胰蛋白酶原基因(cationic trypsinogen,PRSS1)5个外显子进行测序,并分析其各自的临床特征.在4例胰腺炎患者中均出现了PRSS1基因杂合突变,但两家系PRSS1基因突变的位点不同,且临床表现差异较大,其中家系1出现6例糖尿病患者且发病年龄较家系2明显延迟,平均发病年龄为29岁,分析其PRSS1基因发现3号外显子336位碱基存在G→A杂合性突变,为中性突变,表达的氨基酸从赖氨酸(Lys)→赖氨酸(Lys),同时在同一外显子的361位碱基还存在另一个G→A杂合性突变,造成121位的丙氨酸(Ala)被苏氨酸(Thr)所取代,胰蛋白酶原的空间结构发生改变,其与抑制因子的结合位点消失,"保护失败"而产生有活性的胰蛋白酶,造成胰腺自身的消化.而家系2未发现糖尿病患者,其胰腺炎患者的血清肿瘤标志物不增高,先证者(Ⅲ8)在胰腺炎发病过程中表现为CD4 T/CD8 Tcell和乙肝表面抗体(anti-HBs)随病程进展逐渐降低,而Ⅲ7不表现出此现象,分析其PRSS1基因发现3号外显子361位碱基同样存在G→A(c.361G→A)突变,而且在415位还存在一个杂合性突变点T→A(c.415T→A),其中c.415T→A不存在于Ⅲ7.胰蛋白酶原基因存在多种形式的突变,而且与临床表型相关.

Multisite Heterozygous Mutations of PRSS1 Gene and Clinical Characterization of Patients With Hereditary Pancreatitis in The Chinese

In four patients with chronic pancreatitis from two hereditary pancreatitis (HP) families and 63 normal controls, five exons of cationic trypsinogen gene (PRSS1) were amplified by PCR and it's products were analyzed by sequencing, related clinical data were also collected. All the four patients were found mutations in the PRSS1 gene but their clinical feature is absolutely different. Six patients with diabetes mellitus were found in pedigree No. 1, it's members show pancreatitis symptom later, at about 29, the tumor markers (CA19-9, CA72-4) is obviously higher than the patients in pedigree No. 2, two patients with chronic pancreatitis in pedigree No. 2, show symptom earlier without diabetes mellitus, their clinical characterization are different too. The number of CD4+T cell/CD8+T is very low in Ⅲ 8, but Ⅲ 7 is normal, and the level of anti-HBs of Ⅲ 8 is variable in the course of pancreatitis, but the phenomenon was not found in Ⅲ 7. In their PRSS1 gene two guanosine (G) to adenosine (A) mutations were found in PRSS1 exon 3 of pedigree No. 1, one was detected at 336 basyl, the other mutation occurs at 361 basyl. The results of the mutations were Lys →Lys and Ala →Thr. While thymine (T) to adenosine (A) and (guanosine) G→(adenosine) A mutation in PRSS1 exon 3 was detected in the other patient of pedigree No. 2 (Ⅲ 8). One was 361 basyl, the other at 415 basyl. While c.415 T→A was not found in the proband of pedigree No. 2 PRSS1 gene (Ⅲ 7). All of the mutations were heterozygous mutation, that is to say all of the trypsinogen were wild type and mutant type concomitance, the normal and abnormal pathway of active trypsinogen exist partially. At the same time, the mutations of SPINK1 were not observed. Compared with the documents and registration of NCBI, it can be concluded that PRSS1 gene had many kinds of mutations in hereditary pancreatitis, the heterozygous mutations (c.336 G→A, c.415 T→A) were the novel mutations and related with clinical phenotype. What's more, it's the first time that the multisite heterozygous mutations of PRSS1 gene were reported. The presence of the mutations in four patients with chronic pancreatitis, it's absence in their relatives and the strong evolutionary conservation of the mutation, all indicate that the trypsinogen mutation is associated with hereditary pancreatitis and for the first time raises the question whether a gain or a loss of trypsin function participates in the onset of Chinese pancreatitis.