Detection And Analysis Of APC,MUTYH And BMPR1A Mutations In 257Colorectal Polyposis Families

ObjectiveColorectal adenomatous polyposis is a group of hereditary colorectal cancer syndromes,including familial adenomatous polyposis(FAP)and MUTYH-associated polyposis(MAP).Genetic testing of patients with polyposis to identify their pathogenic genes can help clarify the hereditary diagnosis,aid treatment decisions and enable risk prediction and disease control through predictive genetic testing of family members.However,genetic testing of polyposis patients is not commonly performed in China due to the limited knowledge of the disease and genetic testing methods,and detection rates are variable.Previously reported studies have had limited sample sizes and lack comprehensive studies of the gene variant profile.At the same time,colorectal adenomatous polyposis varies significantly in terms of the number and morphology of polyps and the external bowel phenotype,leading to the need for differentiation in treatment and the potential for confusion with other types of tumour syndromes.A more thorough study of the spectrum of adenomatous polyposis variants and an improved understanding of the phenotypic details of the syndromes and the relationship between them is therefore necessary to strengthen the capacity of the relevant departments in the management of polyposis,reduce misdiagnosis and improve the prevention and treatment of polyposis.MethodsThis was a single-centre retrospective study of patients with colorectal adenomatous polyposis registered in the database of the Hereditary Colorectal Cancer Screening and Prevention Centre at Shanghai Changhai Hospital,covering the years 1985 to 2020.Biological specimens including paraffin specimens(surgical specimens or colonoscopic biopsies),peripheral blood and oral mucosal swabs were collected and genetic testing was performed according to the study procedure,using first generation sequencing(Sanger method)and second generation sequencing(NGS)for point mutation detection and multiplexed probe amplification analysis(MLPA)for large segmental variation detection,i.e.first full exon generation sequencing of the APC If the test is negative,MLPA for APC or NGS for multiple genes will be performed according to the clinical pathology.The clinical information collected includes basic information(gender,age,etc.),disease information(age at onset,mode and timing of surgery,family history,etc.)and ancillary findings(endoscopy,imaging,etc.).Once the genetic testing is completed the patients are classified according to their results according to APC variants and non-APC variants.The mutation spectrum of patients with APC-associated polyposis is analysed,and the reported variants are evaluated against relevant database records,and the pathogenicity of unreported variants is judged according to guidelines.For non-APC variant polyposis,the genotype-phenotype correlation was re-evaluated and the disease diagnostic criteria were optimised by reclassifying the nonAPC variants according to their specific genes and determining whether they were consistent with previous diagnostic criteria in the context of the patient’s disease phenotype.ResultsA total of 257 unrelated adenomatous polyposis prevalent patients were included in the study,and a total of 233 carriers of polyposis-associated gene mutations(recessive genes as double allelic variants)were detected,with an overall detection rate of 90.7%.There were 218 cases of APC mutations,with a detection rate of 84.8%.Of these,209 were point mutations,with a detection rate of 81.3%.Large fragment(exon)deletion was found in 9 cases,with a detection rate of 3.5%.Mutation hotspot exon 1309 mutation was found in 29 cases,accounting for 13.3%.There were 21 repeat mutations and 13 unreported mutations.MUTYH and BMPR1 A variants were identified in NGS testing of APC gene mutation negative samples,and no other genes associated with hereditary colorectal cancer were detected.There were 9 carriers of double allele mutations in the MUTYH gene,including 12 missense or nonsense mutations and 4 large segmental deletions.7 patients carried mutations as point mutations and 2 patients carried large segmental deletions.All patients had compound heterozygous mutations,except for one patient whose mutation was a pure point mutation.Two locus mutations(non-European founder mutations)were detected in >1patient.There were 6 carriers of BMPR1 A mutations,all of which were point mutations.6mutations contained 2 splice site variants,2 missense variants,1 nonsense and 1 shift mutation each,of which 2 were newly identified mutations at the splice site.polyposis/bowel cancer phenotypes associated with BMPR1 A included mixed polyp,juvenile polyp,adenomatous polyp,hyperplastic polyp and early onset CRC.ConclusionThis study examined 257 colorectal polyposis samples,the largest sample size study of colorectal polyposis gene variant profiles in China to date.The study identified 15 new variants not seen in the literature or databases,including 13 APC mutations and 2 BMPR1 A mutations.The study identified nine carriers of APC variants using the MLPA test,improving the detection rate of APC variants in patients with adenomatous polyposis.The study defines colorectal polyposis syndrome caused by mutations in the BMPR1 A as BMPR1A-associated polyposis for the first time,providing new insights into the clinical phenotype and treatment options for this genetic variant-associated syndrome and highlighting the significance of genetic testing for such patients.The study used a specially designed genetic testing procedure,and the authors concluded that patients with a negative APC test result should be tested with NGS in conjunction with their clinical presentation,family history and genetic testing techniques,and that patients with BMPR1 A mutations should be alerted to the possibility of having an adenomatous polyposis phenotype.