Mutation Of Related Gene In Chinese Patients With Hereditary Colorectal Polyposis

Background:Familial adenomatous polyposis(FAP),a autosomal dominant inherited disease,characterizes thousands or hundreds of adenoma covering intestine.The morbidity is from 1 over 10000 to 1 over 7000.It is reported that the adenomatous polyposis coli(APC)is the virulence gene to date.With deeper studying,attenuated familial adenomatous polyposis(AFAP)and other special type,such as Gardner syndrome,Peutz-Jeghers syndrome(P-J syndrome)and MYH associated polyposis(MAP),were found one after another,besides classical familial adenomatous polyposis(CFAP).The virulence gene,APC,locates on 5q21-22.The number of it's mutation types is up to 800 on record,which mainly focus on exon 15. The result of the mutation is the formation of truncated APC protein, which could not perform normally and causes the disease.P-J syndrome, considered as one special type of familial hereditary polyposis,is caused by the change of LKB1/STK11,locating on 19p,which makes serin/threonine kinase inactive.It is reported that gene APC and LKB1 is tumor suppressing gene,whose changes lead the tumor to develop.Objective:FAP is a disease with higher genetic predisposition.If not treat,it tends to develop carcinoma.Earlier detection,earlier diagnosis and earlier treatment are more important.The detection of the changes of related gene will help us to find the high risk group,take action to give them reasonable therapy.So we design the experiment to find the available changes in Chinese group.Methods:Our study contains two parts:one was to study Eighteen members from nine FAP pedigrees by using multiplex ligation-dependent probe amplification(MLPA)to detect large fragment deletion of APC gene,and PCR to amplify all exons of APC gene respectively for mutation screening by denaturing high performance liquid chromatograph(DHPLC),whose abnormal elution profile will lead the mutations of related exon to be determined.The other is to study 5 patients with P-J syndrome by using PCR to amplify all exons of LKB1 gene respectively for mutation determination through DNA sequencing and Methylation specific polymerase chain reaction(MSP)to detect whether the promoter region contains 5'CpG island high methylation.Results:In first part,we found two types of mutation in three pedigrees among nine pedigrees,frame shift mutation c.3184₃187 del CAAA in pedigree 2 and c.3925₃929 del AAAAG in pedigree 9,and novel missense mutation c.5432C＞T in pedigree 4,which all lead to the disfunction of APC protein.Development of tumor in Patients of the other six pedigrees may caused by other factors,such as higher methylation of promoter region,the mutation of MYH gene,base excision repair(BER)gene,and the change of splicing site caused by the mutation in intron.We also found there may be a connection between phenotype and genotype.In the second part,germline mutation and somatic mutation in LKB1 were not detected.So did the 5'CpG island methylation of promoter region.The only change found is the mutation, G→T,in intron 1-2 and intron 2-3,which maybe connected to the splice or just gene polymorphism.So other mechanisms maybe involved in, such as large fragment deletion and related protein's changes,as BRG1, STRADalpha,and MO25alpha.Conclusion:The germline mutation of gene APC can lead to the development of FAR Other mechanisms may explain the development of FAP without germline mutation.P-J syndrome,a special type of FAP,is caused by the changes in gene LKB1,which referred to the mutation of gene,methylation of promoter region and so on.The detection of gene can provide experimental evidence for diagnosing the disease and guiding the clinical therapy.