Recognition of genetic syndromes in families with suspected hereditary colon cancer syndromes

Clinical manifestations and STK11 germline mutations in Taiwanese patients with Peutz-Jeghers syndrome

BACKGROUNDS

Clinical manifestations and molecular basis of Taiwanese patients with Peutz-Jeghers syndrome (PJS) were investigated to add the knowledge of phenotype and genotype of the disease.

METHODS

Based on the Pathology Data Bank and the Colorectal Cancer Register, we collected their clinical data. The entire coding sequence of the STK11 gene was amplified and analyzed by sequencing using the genomic DNA.

RESULTS

Fifteen patients diagnosed with PJS from 11 unrelated families were collected until 2015. The median age at the onset of symptoms was 19 years with intussusception as the most frequent presenting symptom. Ten patients developing 11 cancers at various anatomical sites, including two cases of sinonasal cancer, two lung cancers, two breast cancers, two rectal cancers, two gynecological cancers and one small bowel cancer. Five of the deceased patients had died of cancers. The median age of diagnosis of first cancer in the probands was 32 years. Seventy patients (7 of 10) diagnosed before age of 40. Mutations found in eight families included five novel mutations (exon 6, c.843 ins G; exon 8, c.2065 delete A; exon 8, c.G923A, nonsense; exon 6, c.748dupA; and mTOR c.5107dupA) and three previously reported mutations. The other three PJS families without detectable STK11 mutations did not develop malignancies so far.

CONCLUSION

This is the first comprehensive study of patients with Peutz-Jeghers syndrome in the Taiwanese. We have demonstrated that the phenotype of Peutz-Jeghers syndrome varies greatly among the patients. Patients with detectable STK11 mutations have very high risk of developing cancers.

The molecular basis of rectal cancer

The majority of rectal carcinomas are sporadic in nature, and relevant testing for driver mutations to guide therapy is important. A thorough family history is necessary and helpful in elucidating a potential hereditary predilection for a patient's carcinoma. The adequate diagnosis of a heritable tendency toward colorectal carcinoma alters the management of a patient disease and permits the implementation of various surveillance algorithms as preventive measures.

A novel de novo mutation in LKB1 gene in a Chinese Peutz Jeghers syndrome patient significantly diminished p53 activity

Peutz Jeghers syndrome (PJS) is an autosomal dominant disease caused by mutations in the LKB1 gene. We screened for the LKB1 gene mutation in a Chinese PJS patient. Sequence analysis of LKB1 exons showed that there was a novel de novo mis-sense mutation of codon 16 (GAG to GGG) in exon 1 in LKB1 gene in the Chinese PJS patient. Furthermore, we observed that wild type LKB1 expression increased p53 activity, while LKB1 A47G mutation had no such effect on p53 activity, indicating that the mis-sense variant of LKB1 influenced the p53 activation function of LKB1 protein. In addition, real-time RT-PCR analysis revealed that the expression levels of p53 downstream targets were significantly diminished in affected PJS patient compared with those in unaffected parents, further confirming the roles of LKB1 and p53 in PJS pathogenesis. Therefore, a novel PJS associated LKB1 gene mutation is provided, and the roles of LKB1 and p53 in PJS pathogenesis is validated in this research.

Molecular and clinical characteristics in 46 families affected with Peutz-Jeghers syndrome

Germline mutations of the tumor suppressor gene LKB1/STK11 are responsible for the Peutz-Jeghers syndrome (PJS), an autosomal-dominant disorder characterized by mucocutaneous pigmentation, hamartomatous polyps, and an increased risk of associated malignancies. In this study, we assessed the presence of pathogenic mutations in the LKB1/STK11 gene in 46 unrelated PJS families, and also carried genotype-phenotype correlation in regard of the development of cancer in 170 PJS patients belonging to these families. All LKB1/STK11 variants detected with single-strand conformational polymorphism were confirmed by direct sequencing, and those without LKB1/STK11 mutation were further submitted to Southern blot analysis for detection of deletions/rearrangements. Statistical analysis for genotype-phenotype correlation was performed. In 59% (27/46) of unrelated PJS cases, pathogenic mutations in the LKB1/STK11 gene, including 9 novel mutations, were identified. The new mutations were 2 splice site deletion-insertions, 2 missenses, 1 nonsense, and 4 abnormal splice sites. Genotype-phenotype analysis did not yield any significant differences between patients carrying mutations in LKB1/STK11 versus those without mutations, even with respect to primary biliary adenocarcinoma. This study presents the molecular characterization and cancer occurrence of a large cohort of PJS patients, increases the mutational spectrum of LKB1/STK11 allelic variants worldwide, and provides a new insight useful for clinical diagnosis and genetic counseling of PJS families.

Colonic polyps in children and adolescents

Colonic polyps most commonly present with rectal bleeding in children. The isolated juvenile polyp is the most frequent kind of polyp identified in children. 'Juvenile' refers to the histological type of polyp and not the age of onset of the polyp. Adolescents and adults with multiple juvenile polyps are at a significant risk of intestinal cancer. The challenge for adult and pediatric gastroenterologists is determining the precise risk of colorectal cancer in patients with juvenile polyposis syndrome. Attenuated familial adenamatous polyposis (AFAP) can occur either by a mutation at the extreme ends of the adenomatous polyposis coli gene or by biallelic mutations in the mutY homologue (MYH) gene. The identification of MYH-associated polyposis as an autosomal recessive condition has important implications for screening and management strategies. Adult and pediatric gastroenterologists need to be aware of the underlying inheritance patterns of polyposis syndromes so that patients and their families can be adequately evaluated and managed. Colonic polyps, including isolated juvenile polyps, juvenile polyposis syndrome, FAP, AFAP and MYH-associated polyposis, are discussed in the present review.

[Colorectal carcinogenesis. 1. Hereditary predisposition and colorectal cancer]

Tumors arising sporadically represent 70-80% of colorectal cancer (CRC). The two best defined forms of inherited CRC-familial multiple polyposis (FMP) and Hereditary Non-Polyposis Colon Cancer (HNPCC) account respectively for<1% and 2-3% of CRC. These rare genetic syndromes (FMP, HNPCC, Peutz-Jeghers Syndrome) are caused by major predisposing gene mutations (APC gene, MMR gene, BMPR1A. SMAD4,...) and local environmental factors play only a minor role. In the sporadic forms of CRC, 25% have significant genetic predisposition probably related to alleles with weak penetration (APC*I1307K, TGFbR1*6Ala...) and are more strongly affected by environmental factors.

Colorectal cancer screening and surveillance

Screening and surveillance substantially reduce both the incidence and mortality of colorectal cancer. Screening of normal-risk individuals may be accomplished by several methods, including fecal occult blood testing, fiberoptic sigmoidoscopy, double contrast barium enema, and colonoscopy. New technologies for screening are being developed, such as fecal immunochemical testing for blood,fecal DNA testing, and virtual colonoscopy. Patients at increased risk for colorectal cancer, such as those with a positive family history, previous adenomatous polyps or cancer, and inflammatory bowel disease, should be offered more intensive evaluation and surveillance.

Molecular pathogenesis of colorectal cancer: implications for molecular diagnosis

Colorectal cancer is the third leading cause of cancer-related death in both men and woman in industrialized countries. Major advances have been made in our understanding of molecular events leading to formation of adenomatous polyps and cancer. Most colorectal cancers are sporadic, but a significant proportion (5-6%) has a clear genetic background. It is now widely accepted that colorectal carcinogenesis is a multistep process involving the inactivation of a variety of tumor-suppressor and DNA-repair genes and simultaneous activation of certain oncogenes. In addition, epigenetic alterations through aberrant promoter methylation and histone modification have been found to play a major role in the evolution and progression of a large proportion of sporadic colon cancers. Consequently, it is now apparent that individual colorectal cancers may evolve through diverse molecular pathways. In this article, the authors have summarized the current knowledge of molecular pathogenesis in common hereditary syndromes and sporadic forms of colorectal cancer. Novel molecular diagnostic tools for the early diagnosis and prevention of colorectal cancer that have emerged from these insights are discussed.

Genetic testing for inherited colon cancer

The genes associated with each of the inherited syndromes of colon cancer have now been identified, and genetic testing is available for diagnosis. These syndromes include familial adenomatous polyposis, hereditary nonpolyposis colorectal cancer, Peutz-Jeghers syndrome, juvenile polyposis syndrome, and, possibly, Cowden's syndrome. Clinical genetic testing approaches have been developed for each of these syndromes and are now a part of accepted clinical care. Disease-causing mutations can be found in the majority of families affected with one of the inherited syndromes, and, most importantly, once a mutation is found in an index case of the family, relatives can be tested for the presence or absence of that mutation with near 100% accuracy. Cancer screening and management in syndrome families is then based on the results of genetic testing. For the physician to order and properly interpret genetic tests, a basic understanding of the types of mutations that lead to inherited disease and the methods for detecting them is vital. These issues will be presented. Additional clinical issues somewhat unique to genetic testing include genetic counseling and informed consent for genetic testing, both of which will also be reviewed. Often the most difficult aspect of genetic testing is deciding which patients and families should undergo the testing. Furthermore, this issue is quite specific for each of the syndromes. Thus, following presentation of general principles of selection for genetic testing, a detailed approach for identifying persons who should undergo testing for each of the individual syndromes will be given, together with relevant descriptions of the syndromes. Finally, the ongoing work to discover new and possibly more common but less penetrant colon cancer susceptibility genes that cause common familial colon cancer will be presented.