Linkage analysis identifies gene carriers among members of families with hereditary nonpolyposis colorectal cancer

Identification and surveillance of 19 Lynch syndrome families in southern Italy: report of six novel germline mutations and a common founder mutation

Lynch syndrome (LS), or hereditary non-polyposis colorectal cancer (HNPCC), is an autosomal dominant condition responsible for early onset cancer mostly in the colonrectum and endometrium as well as in other organ sites. Lynch syndrome is caused by germline mutations in mismatch repair genes, prevalently in hMSH2, hMLH1, and less frequently in hMSH6 and hPMS2. Twenty-nine non-related index cases with colorectal cancer (CRC) were collected from a region in southeast Italy (Apulia). Among this set of patients, fifteen fulfilled the Amsterdam criteria II. The presence of tumor microsatellite instability (MSI) was assessed in all index cases and 19 (15 AC+/4 AC-) were classified as MSI-H. Mutation analysis performed on all patients, identified 15 pathogenic mutations in hMLH1 and 4 in hMSH2. 4/15 mutations in hMLH1 and 2/4 hMSH2 mutations have not been previously reported. Three previously reported mutations were further investigated for the possibility of a common founder effect. Genetic counseling was offered to all probands and extended to 183 relatives after molecular testing and 85 (46%) mutation carriers were identified. Eighty mutation carriers underwent an accurate clinical and instrumental surveillance protocol. Our results confirm that the identification of LS patients based exclusively on family history may miss patients carrying germline mutations in the MMR genes. Moreover, our results demonstrated that molecular screening and subsequent instrumental surveillance are very effective in identifying CRCs at earlier stages and reducing the number of deaths from secondary cancers in HNPCC patients.

Hereditary non-polyposis colorectal cancer: an updated review

INTRODUCTION

Colorectal cancer is the commonest cause of death due to malignancy in non-smokers in the western countries. The two main hereditary types of colorectal cancer are familial adenomatous polyposis (FAP) and hereditary non-polyposis colorectal cancer (HNPCC), constituting approximately 10% of all cases of colorectal cancer. The main aim of this review is to reappraise the current advances in the genetics and diagnosis of HNPCC.

METHODS

A Medline search was carried out to identify papers published from 1970 to 1999 on HNPCC. Embase and Cochrane databases were also searched. Reference lists of retrieved articles were carefully searched for additional articles.

RESULTS AND CONCLUSIONS

Recent technological advances in the genetics of HNPCC have refined the criteria for diagnosis and management of HNPCC, however current policies regarding the testing of pedigrees are not clearly established. We believe that with the rapid development in this area definitive clinical guidelines will need to be available in future for the management of HNPCC.

Genetic testing in hereditary colorectal cancer: indications and procedures

Approximately 25% of colorectal cancers occur in younger individuals or those with a personal or family history of the disease, suggesting a heritable susceptibility. The minority of these cases are accounted for by one of the well-described hereditary colorectal cancer syndromes, familial adenomatous polyposis (FAP) and hereditary nonpolyposis colorectal cancer (HNPCC). The recent identification and cloning of the genes responsible for FAP and HNPCC, along with other colon cancer susceptibility genes, has led to the wide-spread availability of genetic testing for hereditary colorectal cancer. Genetic testing raises clinical, ethical, legal, and psychosocial questions that must urgently be discussed. This review highlights areas of knowledge and uncertainty about genetic predisposition testing for colorectal cancer and provides clinicians with practical recommendations regarding the proper indications and procedures for this testing.

Small bowel carcinoma in hereditary nonpolyposis colorectal cancer

A 53-yr-old man, a member of a hereditary nonpolyposis colorectal cancer (HNPCC) family, with previous colonoscopic polypectomies, presented for persisting vomiting and marked signs of dehydration. Previous radiological and endoscopic examinations of the upper digestive tract were negative, with the exception of the presence of a duodenal adenomatous polyp. Enteroclysis led to a diagnosis of obstruction at the Treitz angle due to a moderately differentiated adenocarcinoma. Microsatellite instability was demonstrated in the DNA extracted from the tumor. The patient was the carrier of a mutation in the intron 13 of the hMLH1 gene, one of the four mismatch repair genes known to be responsible for HNPCC.

Colorectal and extracolonic cancer variations in MLH1/MSH2 hereditary nonpolyposis colorectal cancer kindreds and the general population

PURPOSE

This clinical case review aimed to identify phenotypic variations in colorectal and extracolonic cancer expression between hereditary nonpolyposis colorectal cancer (HNPCC) families with MLH1 and MSH2 germline mutations and the general population.

METHODS

Colorectal cancer onset and site distribution were compared among 67 members of MLH1 kindreds, 45 members of MSH2 kindreds, and 1,189 patients from the general population. Synchronous and metachronous cancer rates, tumor stage, extracolonic cancer incidence, and survival were also compared.

RESULTS

Mean ages of colorectal cancer onset were 44, 46, and 69 years for MLH1, MSH2, and the general population, respectively (P < 0.001). More proximal and fewer distal colon cancers were noted in HNPCC than the general population (P < 0.001, P = 0.04). Site distribution showed disparity of rectal cancers (8 percent MLH1 vs. 28 percent MSH2; P = 0.01) based on genotypes. Overall, synchronous colorectal cancer rates were 7.4, 6.7, and 2.4 percent for MLH1, MSH2, and the general population, respectively (P = 0.016). Annual metachronous colorectal cancer rates were 2.1, 1.7, and 0.33 percent for MLH1, MSH2, and the general population, respectively (P = 0.041). Colorectal cancer stage presentation was lower in HNPCC than the general population (P = 0.0028). Extracolonic cancers were noted in 33 percent of MSH2 patients, compared with 12 percent of MLH1 patients and 7.3 percent of the general population with colorectal cancers (P < 0.001). Combined MLH1 and MSH2 ten-year survival was 68.7 percent compared with 47.8 percent for the general population (P = 0.009 stage stratified, hazard ratio 0.57).

CONCLUSION

The presence of rectal cancer should not preclude the diagnosis of HNPCC, because the incidence of rectal cancer in MSH2 was comparable with that in the general population. Phenotypic variations, including the preponderance of extracolonic cancers in MSH2 patients, did not result in survival differences between genotypic subgroups. These phenotypic features of HNPCC genotypes may have clinical significance in the design of specific screening, surveillance, and follow-up for affected individuals.

Cumulative incidence of colorectal and extracolonic cancers in MLH1 and MSH2 mutation carriers of hereditary nonpolyposis colorectal cancer

The extracolonic tumor spectrum of hereditary nonpolyposis colorectal cancer (HNPCC) includes cancer of the endometrium, ovaries, stomach, biliary tract, and urinary tract. This study was designed to determine the penetrance of colorectal and extracolonic tumors in HNPCC mutation carriers. Forty-nine patients (22 females and 27 males) were identified with an MSH2 germline mutation, and 56 patients (28 females and 28 males) were identified with an MLH1 I mutation. Cumulative incidence by age 60 (lifetime risk) and mean age of cancer diagnosis were compared. The lifetime risk of extracolonic cancers in MSH2 and MLH1 carriers was 48% and 11%, respectively (P = 0.016). Extracolonic cancer risk in MSH2 females and males was 69% and 34%, respectively (P = 0.042). Mean age of extracolonic cancer diagnosis was significantly older for MSH2 males than females (55.4 vs. 39.0, P = 0.013). No difference was observed in colorectal cancer risk between MLH1 and MSH2 carriers (84% vs. 71%). Colorectal cancer risk was 96% in MSH2 males compared to 39% in MSH2 females (P = 0.034). No differences in colorectal and extracolonic cancer risks between MLH1 females and males were identified. The risk of extracolonic cancer by age 60 was greater in MSH2 mutation carriers than in MLH1 carriers. Gender differences in colorectal and extracolonic cancer risk were observed for MSH2 carriers only. These phenotypic features of HNPCC genotypes may have clinical significance in the design of genotype-specific screening, surveillance, and follow-up for affected individuals.

An update of HNPCC (Lynch syndrome)

Genetic epidemiology studies of colorectal cancer (CRC) can identify persons who are at inordinately high risk and who thereby might benefit from targeted early detection and primary prevention programs, inclusive of prophylactic surgery in selected cases. The discipline of molecular genetics has identified germline mutations that include APC in familial adenomatous polyposis (FAP) and mutator genes, namely MSH2, MLH1, PMS1, and PMS2 in hereditary nonpolyposis colorectal cancer (HNPCC). These discoveries have significantly enhanced our ability to identify individuals whose cancer destiny can literally be determined at birth. This review updates HNPCC's differential diagnosis, heterogeneity, tumor spectrum, newly found evidence of accelerated colonic adenoma to CRC, survival advantage, and currently available surveillance and management programs. Emphasis has been on how knowledge of the genetics and natural history of HNPCC can be used effectively to promote early diagnosis or prevention of cancer.

Familial risk and colorectal cancer

Familial risk of colon cancer is common. The rare syndromes of FAP and HNPCC account for a small fraction of familial cases. A working knowledge of these syndromes is important, however, because appropriate management can prevent most cases of colon cancer in families with these conditions. Furthermore, the genes that give rise to FAP and HNPCC have been identified, and genetic testing to find gene carriers in affected families is now commercially available. In addition to the syndromes, colon cancer commonly clusters in families. The risk of colon cancer is two to threefold increased when a first-degree relative is affected with this malignancy. The risk is further increased if multiple first-degree relatives have colon cancer or if a diagnosis in a relative is made at an age of 50 years or younger. The genetic causes of this more commonly observed of familial clustering have not been clarified, but screening based on the degree of familial risk has been suggested.