Novel mutations in the LKB1/STK11 gene in Dutch Peutz-Jeghers families

A novel pathogenic splice site variation in STK11 gene results in Peutz-Jeghers syndrome

Background

Peutz–Jeghers syndrome (PJS) is a rare autosomal dominantly inherited disease resulting in multiple gastrointestinal hamartomatous polyps, mucocutaneous pigmentation, and an increased risk of various types of cancer, and is caused by variations in the serine/threonine protein kinase STK11 (LKB1).

Methods

STK11 gene variations were identified by analyzing STK11 cDNA and genomic DNA. Minigenes carrying the wild‐type and mutant sequences were subjected to in vitro splicing assay to dissect the features of these mutations. The different distribution of wild‐type and mutant protein in cells were tested by Immunofluorescence assays and the functional analysis of the variation were performed using Western blot.

Results

A novel heterozygous splice‐acceptor site variation (c.921‐2 A>C) in intron 7 of the STK11 gene which is co‐segregates with the PJS phenotypes in the proband and all the affected family members and three previously reported variations (c.180C>G, c.580G>A, c.787_790del) were identified in the four families. The c.921‐2 A>C substitution resulted in the inactivation of a splice site and the utilization of a cryptic splice acceptor site surrounding exon 8, generating three different aberrant RNA transcripts, leading to frameshift translation and protein truncation. The results of minigenes indicated that the spliceosome can use a variety of 3’ acceptor site sequences to pair with a given 5’ donor site. The immunofluorescent visualization showed that the distribution of mutant STK11 was different from that of wild‐type STK11, suggesting the mutation may be the causative effect on the dysfunction of the mutant protein. The rescue experiments indicated that the failure of suppressing mTOR phosphorylation by shRNA STK11 could be eliminated by supply of wild‐type STK11 rather than mutant STK11.

Conclusion

We identified a novel heterozygous mutation (c.921‐2 A>C) in the STK11 in a Chinese PJS family. Haploinsufficiency of STK11 might contribute to the pathogenesis of the disease.

A lesson from a reported pathogenic variant in Peutz-Jeghers syndrome: a case report

Peutz-Jeghers syndrome (PJS) is a rare autosomal dominant disorder characterized by mucocutaneous hyperpigmentation, gastrointestinal (GI) hamartmatous polyps, and an increased risk of various malignancies. Pathogenic variants in the LKB1 tumor suppressor gene (also known as STK11) are the major cause of PJS. In this study, compound heterozygous variants of LKB1, c.890G > A/ c.1062C > G and del(exon1)/ c.1062C > G, were identified in two sporadic Chinese PJS cases respectively. Although all these three variants had been related to the autosomal dominant PJS in previous studies, all evidences collected in this study including de novo data, segregation data, population data, in-silico data, and functional data indicated that del(exon1) and c.890G > A are pathogenic in these two PJS families rather than c.1062C > G. This finding would contribute to genetic counseling for individuals carrying the variant c.1062C > G with or without PJS phenotypes. Moreover, this finding reminds genetic counselors that it is necessary to reevaluate the pathogenicity of reported variants in a known Mendelian disorder in order to avoid a misleading decision.

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.

A Clinical and Molecular Genetic Study in 11 Chinese Children With Peutz-Jeghers Syndrome

OBJECTIVES

Peutz-Jeghers syndrome (PJS) is caused by the germline mutations in serine/threonine kinase 11 (STK11) gene. The aim of the present study was to investigate the spectrum of STK11 gene mutations using multiplex ligation-dependent probe amplification (MLPA) assay in combination with direct sequencing in Chinese children with PJS.

METHODS

Nine children who met the clinical criteria for PJS and 2 presumed patients with PJS were enrolled in the present study. Patients' clinical information on polyp characteristics, polyp-related complications, family histories, and so on were reviewed and analyzed. After obtaining informed consent, we performed a mutation analysis of STK11 gene in 11 Chinese patients using MLPA assay and direct sequencing.

RESULTS

By means of MLPA method, we detected exonic deletions in 5 patients. In details, 1 patient had the complete deletion of all 10 exons, 3 patients showed deletions of promoter region and exon 1, and 1 patient had exon deletions from 1 to 9. By direct sequencing of the coding region of STK11 gene, we identified point mutations in 4 patients at c.548T>G/p.Leu183Arg, c.580G>T/p.Asp194Tyr, c.152_153insGG/Asp53GlyfsX12, and c.631delC/Arg211GlyfsX76, respectively, and 3 of them are novel mutations. We failed to find any mutation in left 2 patients who met the clinical criteria of PJS.

CONCLUSIONS

MLPA plus direct sequencing revealed large genomic deletions of STK11 gene in Chinese children with PJS and increased the detecting rate of STK11 gene mutations in Chinese patients with PJS. MLPA combined with direct sequencing could serve as a better strategy for the genetic diagnosis of PJS in Chinese population.

Energy sensing and cancer: LKB1 function and lessons learnt from Peutz-Jeghers syndrome

We describe in this review increasing evidence that loss of LKB1 kinase in Peutz-Jeghers syndrome (PJS) derails the existing natural balance between cell survival and tumour growth suppression. LKB1 deletion can plunge cells into an energy/oxidative stress-induced crisis which leads to the activation of alternative and often carcinogenic pathways to maintain cellular energy levels. It therefore appears that although LKB1 deficiency can suppress oncogenic transformation in the short term, it can ultimately lead to more progressed and malignant phenotypes by driving abnormal cell differentiation, genomic instability and increased tumour heterogeneity.

Clinical characteristics and STK11 gene mutations in Chinese children with Peutz-Jeghers syndrome

Background

Peutz-Jeghers syndrome (PJS) is a rare autosomal dominant inherited disease characterized by gastrointestinal hamartomatous polyps and mucocutaneous melanin spots. Germline mutation of the serine/threonine kinase 11 (STK11) gene are responsible for PJS. In this study, we investigated the clinical characteristics and molecular basis of the disease in Chinese children with PJS.

Methods

Thirteen children diagnosed with PJS in our hospital were enrolled in this study from 2011 to 2015, and their clinical data on polyp characteristics, intussusceptions events, family histories, etc. were described. Genomic DNA was extracted from whole-blood samples from each subject, and the entire coding sequence of the STK11 gene was amplified by polymerase chain reaction and analyzed by direct sequencing.

Results

The median age at the onset of symptoms was 2 years and 4 months. To date, these children have undergone 40 endoscopy screenings, 17 laparotomies and 9 intussusceptions. Polyps were found in the stomach, duodenum, small bowel, colon and rectum, with large polyps found in 7 children. Mutations were found in eleven children, including seven novel mutations (c.481het_dupA, c.943_944het_delCCinsG, c.397het_delG, c.862 + 1G > G/A, c.348_349het_delGT, and c.803_804het_delGGinsC and c.121_139de l19insTT) and four previously reported mutations (c.658C > C/T, c.890G > G/A, c.1062 C > C/G, and c.290 + 1G > G/A). One PJS patient did not have any STK11 mutations.

Conclusions

The polyps caused significant clinical consequences in children with PJS, and mutations of the STK11 gene are generally the cause of PJS in Chinese children. This study expands the spectrum of known STK11 gene mutations.

STK11 domain XI mutations: candidate genetic drivers leading to the development of dysplastic polyps in Peutz-Jeghers syndrome

Peutz-Jeghers syndrome (PJS) is a rare hereditary disorder resulting from mutations in serine/threonine kinase 11 (STK11) and characterized by gastrointestinal (GI) hamartomatous polyps, mucocutaneous pigmentation, and an increased risk for specific cancers. Little is known about the genetic implications of specific STK11 mutations with regard to their role in dysplastic and malignant transformation of GI polyps. Peripheral blood genomic DNA samples from 116 Chinese PJS patients from 52 unrelated families were investigated for STK11 mutations. Genotype-phenotype correlations were investigated. The mutation detection rate was 67.3% (51.9% point mutations, 15.4% large deletions). Fourteen out of the 25 point mutations identified were novel. Nearly one-third of all mutations, 8/27 (29.6%), were in exon 7, the shortest out of the nine exons. Strikingly, mutations affecting protein kinase domain XI, encoded in part by exon 7, correlated with a 90% (9/10) incidence of GI polyp dysplasia. In contrast, only two out of 17 (11.8%) nondomain XI mutations were linked to polyp dysplasia (P = 0.0001). The extent of the association between dysplasia and the development of GI-related cancers is currently unknown but our results highlight a novel STK11 genotype-phenotype association as the basis for future genetic counseling and basic research studies.

Exome sequencing revealed novel germline mutations in Chinese Peutz-Jeghers syndrome patients

BACKGROUND AND AIMS

Peutz-Jeghers Syndrome (PJS) is an autosomal dominant disorder which predisposes to the development of various cancers. Germline mutation in the serine/threonine kinase 11 gene (STK11) is known as one of the major causes of PJS. However, a notable proportion of PJS samples do not carry any mutation in STK11, suggesting possible genetic heterogeneity in the disease and the existence of other causative variants.

METHODS AND RESULTS

In order to identify other germline variants in the coding regions of the genome that are associated with PJS, we performed exome sequencing in three Chinese individuals with PJS and identified 16 common germline variants (12 protein-coding including STK11, 4 in pre-microRNAs). We further validated protein-coding variants in six PJS individuals (three with wild-type STK11) and predicted the functional impact. As result, we found that 7 coding variants are likely to have functional impacts. Especially, we identified 2 new germline variants which are represented in all six PJS samples and are independent of STK11 mutation.

CONCLUSIONS

Our study provided an exomic view of PJS. The germline variants identified in our analysis may help to resolve the complex genetic background of the disease and thus lead to the discovery of novel causative variants of PJS.

High Resolution Melting analysis as a rapid and efficient method of screening for small mutations in the STK11 gene in patients with Peutz-Jeghers syndrome

Background

Peutz-Jeghers syndrome (PJS) is a rare hereditary syndrome characterized by the occurrence of hamartomatous polyps in the gastrointestinal tract, mucocutaneous pigmentation and increased risk of cancer in multiple internal organs. Depending on the studied population, its incidence has been estimated to range from 1:200 000 even up to 1:50 000 births. Being an autosomal disease, PJS is caused in most cases by mutations in the STK11 gene.

Methods

The majority of causative DNA changes identified in patients with PJS are small mutations and, therefore, developing a method of their detection is a key aspect in the advancement of genetic diagnostics of PJS patients. We designed 13 pairs of primers, which amplify at the same temperature and enable examination of all coding exons of the STK11 gene by the HRM analysis.

Results

In our group of 41 families with PJS small mutations of the STK11 gene were detected in 22 families (54%). In the remaining cases all of the coding exons were sequenced. However, this has not allowed to detect any additional mutations.

Conclusions

The developed methodology is a rapid and cost-effective screening tool for small mutations in PJS patients and makes it possible to detect all the STK11 gene sequence changes occurring in this group.

Cancer problem in Peutz-Jeghers syndrome

Peutz–Jeghers syndrome is a rare autosomal dominantly inherited condition, characterized by the presence of hamartomatous gastrointestinal polyps and mucocutaneous pigmentation. Patients with this syndrome can be associated with other neoplasms such as ovarian neoplasms known as sex-cord tumor with annular tubules that are associated in one third of the cases with this syndrome and other types of malignancies. We report a 42-year-old woman with a history of Peutz–Jeghers Syndrome and bilateral breast cancer that presented with abnormal uterine bleeding. Total abdominal hysterectomy with bilateral salpino-oophorectomy was done and an ovarian sex cord tumor with annular tubules was incidentally diagnosed. By reviewing literatures and in agreement with previous studies we suggest routine screening for malignancies in patients with Peutz–Jeghers syndrome.

Colon cancer associated genes exhibit signatures of positive selection at functionally significant positions

Background

Cancer, much like most human disease, is routinely studied by utilizing model organisms. Of these model organisms, mice are often dominant. However, our assumptions of functional equivalence fail to consider the opportunity for divergence conferred by ~180 Million Years (MY) of independent evolution between these species. For a given set of human disease related genes, it is therefore important to determine if functional equivalency has been retained between species. In this study we test the hypothesis that cancer associated genes have different patterns of substitution akin to adaptive evolution in different mammal lineages.

Results

Our analysis of the current literature and colon cancer databases identified 22 genes exhibiting colon cancer associated germline mutations. We identified orthologs for these 22 genes across a set of high coverage (>6X) vertebrate genomes. Analysis of these orthologous datasets revealed significant levels of positive selection. Evidence of lineage-specific positive selection was identified in 14 genes in both ancestral and extant lineages. Lineage-specific positive selection was detected in the ancestral Euarchontoglires and Hominidae lineages for STK11, in the ancestral primate lineage for CDH1, in the ancestral Murinae lineage for both SDHC and MSH6 genes and the ancestral Muridae lineage for TSC1.

Conclusion

Identifying positive selection in the Primate, Hominidae, Muridae and Murinae lineages suggests an ancestral functional shift in these genes between the rodent and primate lineages. Analyses such as this, combining evolutionary theory and predictions - along with medically relevant data, can thus provide us with important clues for modeling human diseases.

Germline mutation analysis of STK11 gene using direct sequencing and multiplex ligation-dependent probe amplification assay in Korean children with Peutz-Jeghers syndrome

Background and Aims Peutz-Jeghers syndrome is an autosomal, dominantly inherited disease characterized by mucocutaneous hyperpigmentation and hamartomatous polyps of the gastrointestinal tract. In this study, mutation analysis of the STK11 gene was performed to establish the genetic background of Peutz-Jeghers syndrome in Korean children.Methods This study included 17 children who were diagnosed with Peutz-Jeghers syndrome based on clinical diagnostic criteria between July 2006 and December 2007.The clinical records of these children were reviewed retrospectively.Genomic DNA was extracted from the blood samples of each patient and used for direct sequencing and the MLPA (multiplex ligation-dependent probe amplification)assay.Results By direct sequencing, mutations in the STK11 gene were observed in five of 17 (29.4%) children with Peutz-Jeghers syndrome. Missense mutations were observed in four, and a frameshift mutation in one. All these mutations were present in the kinase domain of the STK11 gene. By MLPA analysis, mutations in the STK11 gene were observed in six (35.3%) children—exonic deletions were observed in five and exonic duplication in one. Conclusions The detection rate of STK11 gene mutations by direct sequencing is relatively low, even in children clinically diagnosed with Peutz-Jeghers syndrome. With the introduction of the MLPA assay as a new cytogenetic technique, large deletions and exonic duplications could also be detected in children with PJS. In the future, these results may be useful for the genetic diagnosis of Peutz-Jeghers syndrome in Korean children.

Determining the frequency of de novo germline mutations in DNA mismatch repair genes

BACKGROUND

Carriers of a germline mutation in a DNA mismatch repair (MMR) gene--that is, persons with Lynch syndrome--have substantially high risks of colorectal (CRC), endometrial, and several other cancers. The proportion of carriers who have de novo mutations (not inherited from either parent) is not known. This study reports a case series of de novo mutations in MMR genes and estimates the frequency of de novo mutation in MMR genes using the Colon Cancer Family Registry.

METHODS

Screening for germline MLH1, MSH2, MSH6, and PMS2 mutations was performed for all incident CRC cases recruited from cancer registries (population based probands) displaying microsatellite instability (MSI) or loss of expression of MMR genes by immunohistochemistry (IHC) and probands with CRC in multi-case families recruited from clinics (clinic based probands), regardless of MSI or IHC status. All relatives of probands with a pathogenic mutation who donated a blood sample underwent testing for the mutation identified in the proband.

RESULTS

Of 261 probands (202 clinic based, 59 population based) with MMR gene mutations for whom it was possible to determine the origin of the mutation, six (2.3%, 95% CI 0.9% to 5.0%) were confirmed as de novo, and the remaining 255 (97.7%, 95% CI 95.0% to 99.1%) were inherited. Of the de novo mutation carriers, three were clinic based probands (1.5%, 95% CI 0.3% to 4.5%) and three were population based probands (5.1%, 95% CI 1.2% to 14.5%). Two were in MLH1, three in MSH2, and one in MSH6.

CONCLUSION

De novo MMR gene mutations are uncommon causes of Lynch syndrome.

Liver kinase B1 (LKB1) in the pathogenesis of epithelial cancers

LKB1 acts as a master kinase, with its major protein targets being the family of AMPKs. Through activation of multiple signaling pathways, LKB1's main physiologic functions involve regulating cellular growth, metabolism, and polarity. Germline mutations in LKB1 result in Peutz-Jeghers Syndrome, a rare cancer susceptibility syndrome. In addition, multiple LKB1 mutations have been identified in sporadic cancers, especially those of the lung. Recent studies from a variety of murine models have helped characterize LKB1's role in the pathogenesis of epithelial cancers. In some tumor types, LKB1 might function chiefly to suppress cell growth or invasion, while in other cases, it may serve to prevent metastasis. Moreover, molecular signatures of individual tumors likely influence LKB1's operational role, as multiple studies have shown that LKB1 can synergize with other tumor suppressors and/or oncogenes to accelerate tumorigenesis. To date, LKB1 has been considered mainly a tumor suppressor; however, some studies have suggested its potential oncogenic role, mainly through the suppression of apoptosis. In short, LKB1 is a tissue and context-specific kinase. This review aims to summarize our current understanding of its role in the pathogenesis of epithelial cancers.

Germline mutation analysis of STK11 gene using direct sequencing and multiplex ligation-dependent probe amplification assay in Korean children with Peutz-Jeghers syndrome

Background and Aims Peutz-Jeghers syndrome is an autosomal, dominantly inherited disease characterized by mucocutaneous hyperpigmentation and hamartomatous polyps of the gastrointestinal tract. In this study, mutation analysis of the STK11 gene was performed to establish the genetic background of Peutz-Jeghers syndrome in Korean children.Methods This study included 17 children who were diagnosed with Peutz-Jeghers syndrome based on clinical diagnostic criteria between July 2006 and December 2007.The clinical records of these children were reviewed retrospectively.Genomic DNA was extracted from the blood samples of each patient and used for direct sequencing and the MLPA (multiplex ligation-dependent probe amplification)assay.Results By direct sequencing, mutations in the STK11 gene were observed in five of 17 (29.4%) children with Peutz-Jeghers syndrome. Missense mutations were observed in four, and a frameshift mutation in one. All these mutations were present in the kinase domain of the STK11 gene. By MLPA analysis, mutations in the STK11 gene were observed in six (35.3%) children—exonic deletions were observed in five and exonic duplication in one. Conclusions The detection rate of STK11 gene mutations by direct sequencing is relatively low, even in children clinically diagnosed with Peutz-Jeghers syndrome. With the introduction of the MLPA assay as a new cytogenetic technique, large deletions and exonic duplications could also be detected in children with PJS. In the future, these results may be useful for the genetic diagnosis of Peutz-Jeghers syndrome in Korean children.

A De Novo mutation of STK11 gene in a Chinese patient with Peutz-Jeghers syndrome

Peutz-Jeghers syndrome (PJS) is an autosomal-dominant inherited disorder characterized by mucocutaneous pigmentation, hamartomatous polyposis of the gastrointestinal tract, and an increased risk for the development of both gastrointestinal and extraintestinal malignancies. Germline mutation of the STK11 gene, which encodes a serine-threonine kinase, is responsible for PJS. We collected blood samples from a Chinese PJS family consisting of a total of four individuals (one male and three females) including one PJS patient. The whole coding region of STK11 was amplified by polymerase chain reaction and products analyzed by direct sequencing. Molecular analysis of the STK11 gene in this case of PJS revealed a substitution of thymine 217 for adenine (C.217T > A) in exon 1, resulting in a change of codon 73 from cysteine to serine (C73S). The point mutation was not found in normal individuals in this PJS family or in 100 control individuals. The results presented here enlarge the spectrum of mutations of the STK11 gene by identifying a de novo mutation in a PJS patient and further support the hypothesis that STK11 mutations are disease-causing mutations for PJS.

Immunohistological evidence for Wnt-signaling activation in Peutz-Jeghers polyposis

OBJECTIVE

Molecular pathogenesis of gastrointestinal polyposis in Peutz-Jegher's syndrome (PJS) has been linked to the loss-of-function mutation of LKB1. Recent functional genetic studies have pointed out that LKB1 plays a physiological role in controlling the Wnt-signaling pathway and activation of the pathway as a consequence of LKB1 haploinsufficiency might be responsible for the development of harmatomatous polyps. This study aimed to look for immunohistochemical evidence of Wnt-signaling activation in PJS polyps.

METHOD

Beta-catenin immunohistochemistry patterns were evaluated in gastrointestinal polyps from five cases of PJS. All patients were also evaluated for germline mutations of LKB1 and somatic mutations of beta-catenin in the polyps.

RESULTS

Four of the five cases had germline mutations of LKB1, including two novel mutations, a one-base insertion at codon 53 and a large deletion encompassing exon 3 (codon 136-155). PJS polyps from all patients showed generalized membrane and cytoplasmic localizations of beta-catenin along the mucosal endothelium. Polyps from two cases with LKB1 mutations revealed moderate-intensity nuclear staining in approximately 20 and 70% of the polyps.

CONCLUSION

The study offers additional evidence of Wnt-signaling activation in PJS polyp development at the tissue level, although the degree of up-regulation was not as high as has been found in Wnt-associated neoplasms.

Closely spaced multiple mutations as potential signatures of transient hypermutability in human genes

Data from diverse organisms suggests that transient hypermutability is a general mutational mechanism with the potential to generate multiple synchronous mutations, a phenomenon probably best exemplified by closely spaced multiple mutations (CSMMs). Here we have attempted to extend the concept of transient hypermutability from somatic cells to the germline, using human inherited disease-causing multiple mutations as a model system. Employing stringent criteria for data inclusion, we have retrospectively identified numerous potential examples of pathogenic CSMMs that exhibit marked similarities to the CSMMs reported in other systems. These examples include (1) eight multiple mutations, each comprising three or more components within a sequence tract of <100 bp; (2) three possible instances of "mutation showers"; and (3) numerous highly informative "homocoordinate" mutations. Using the proportion of CpG substitution as a crude indicator of the relative likelihood of transient hypermutability, we present evidence to suggest that CSMMs comprising at least one pair of mutations separated by < or =100 bp may constitute signatures of transient hypermutability in human genes. Although this analysis extends the generality of the concept of transient hypermutability and provides new insights into what may be considered a novel mechanism of mutagenesis underlying human inherited disease, it has raised serious concerns regarding current practices in mutation screening.

Hijacking the chromatin remodeling machinery: impact of SWI/SNF perturbations in cancer

There is increasing evidence that alterations in chromatin remodeling play a significant role in human disease. The SWI/SNF chromatin remodeling complex family mobilizes nucleosomes and functions as a master regulator of gene expression and chromatin dynamics whose functional specificity is driven by combinatorial assembly of a central ATPase and association with 10 to 12 unique subunits. Although the biochemical consequence of SWI/SNF in model systems has been extensively reviewed, the present article focuses on the evidence linking SWI/SNF perturbations to cancer initiation and tumor progression in human disease.

Carney complex and lentiginosis

Initially described as the 'complex of myxomas, spotty skin pigmentation and endocrine overactivity,' Carney complex (CNC) is known as an autosomal dominant multiple neoplasia syndrome involving skin and cardiac myxomas, pigmented skin lesions and endocrine tumors. Pigmented cutaneous manifestations in CNC are important diagnostically because they can be used for the early detection of the disease and, thus, the prevention of life-threatening complications of CNC related to heart myxomas and endocrine abnormalities. Specific for the disease skin lesions are present in more than half of the CNC patients. A major challenge is to distinguish pigmented skin lesions associated with CNC from other skin pathology, and thus accurately estimate the risk of cancer in affected patients; curiously, patients with CNC do not appear to have predisposition to skin cancers whereas this is not the case with other genetic syndromes associated with melanotic and other cutaneous lesions. In this paper, we review the current knowledge on cutaneous pathology associated with CNC and the most recent data on the molecular basis of the disease.

The molecular mechanisms that underlie the tumor suppressor function of LKB1

Germline mutations of the LKB1 tumor suppressor gene result in Peutz-Jeghers syndrome (PJS) characterized by intestinal hamartomas and increased incidence of epithelial cancers. Inactivating mutations in LKB1 have also been found in certain sporadic human cancers and with particularly high frequency in lung cancer. LKB1 has now been demonstrated to play a crucial role in pulmonary tumorigenesis, controlling initiation, differentiation, and metastasis. Recent evidences showed that LKB1 is a multitasking kinase, with great potential in orchestrating cell activity. Thus far, LKB1 has been found to play a role in cell polarity, energy metabolism, apoptosis, cell cycle arrest, and cell proliferation, all of which may require the tumor suppressor function of this kinase and/or its catalytic activity. This review focuses on remarkable recent findings concerning the molecular mechanism by which the LKB1 protein kinase operates as a tumor suppressor and discusses the rational treatment strategies to individuals suffering from PJS and other common disorders related to LKB1 signaling.

Report on de-novo mutation in the MSH2 gene as a rare event in hereditary nonpolyposis colorectal cancer

OBJECTIVE

Hereditary nonpolyposis colorectal cancer (HNPCC) is an autosomal dominant predisposition for early-onset colorectal cancer and associated tumour types caused by mutations in DNA mismatch repair genes, mainly MLH1 and MSH2. The Amsterdam criteria, stressing familial tumour events, as well as the less stringent Bethesda criteria, help to raise suspicion of HNPCC.

RESULT

Mutation screening in a colon cancer patient of young age but negative family history revealed the MSH2 splice site mutation c.2006-2A>G. This mutation was present in all three germ cell layers in the patient, but absent in her biological parents, reporting the second case of de-novo germline mutation in MSH2.

CONCLUSION

Our findings suggest that at least in approximately 1% of mutation-positive cases, a de-novo event might be involved. The identification of a newly evolved rare mutation calls for alertness and encourages the application of the Bethesda guidelines and certain clinical and histopathological features to define candidates for HNPCC gene mutation screening despite a negative family history.

Congenital disease SNPs target lineage specific structural elements in protein kinases

The catalytic domain of protein kinases harbors a large number of disease-causing single nucleotide polymorphisms (SNPs) and common or neutral SNPs that are not known or hypothesized to be associated with any disease. Distinguishing these two types of polymorphisms is critical in accurately predicting the causative role of SNPs in both candidate gene and genome-wide association studies. In this study, we have analyzed the structural location of common and disease-associated SNPs in the catalytic domain of protein kinases and find that, although common SNPs are randomly distributed within the catalytic core, known disease SNPs consistently map to regulatory and substrate binding regions. In particular, a buried side-chain network that anchors the flexible activation loop to the catalytic core is frequently mutated in disease patients. This network was recently shown to be absent in distantly related eukaryotic-like kinases, which lack an exaggerated activation loop and, presumably, are not regulated by phosphorylation.

Genetic defects underlying Peutz-Jeghers syndrome (PJS) and exclusion of the polarity-associated MARK/Par1 gene family as potential PJS candidates

LKB1/STK11 germline inactivations are identified in the majority (66-94%) of Peutz-Jeghers syndrome (PJS) patients. Therefore, defects in other genes or so far unidentified ways of LKB1 inactivation may cause PJS. The genes encoding the MARK proteins, homologues of the Par1 polarity protein that associates with Par4/Lkb1, were analyzed in this study because of their link to LKB1 and cell polarity. The genetic defect underlying PJS was determined through analysis of both LKB1 and all four MARK genes. LKB1 point mutations and small deletions were identified in 18 of 23 PJS families using direct sequencing and multiplex ligation-dependent probe amplification analysis identified exon deletions in 3 of 23 families. In total, 91% of the studied families showed LKB1 inactivation. Furthermore, a MARK1, MARK2, MARK3 and MARK4 mutation analysis and an MARK4 quantitative multiplex polymerase chain reaction analysis to identify exon deletions on another eight PJS families without identified LKB1 germline mutation did not identify mutations in the MARK genes. LKB1 defects are the major cause of PJS and genes of the MARK family do not represent alternative PJS genes. Other mechanisms of inactivation of LKB1 may cause PJS in the remaining families.

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.

STK11 status and intussusception risk in Peutz-Jeghers syndrome

BACKGROUND

Peutz-Jeghers syndrome (PJS) is caused by germline STK11 mutations and characterised by gastrointestinal polyposis. Although small bowel intussusception is a recognised complication of PJS, risk varies between patients.

OBJECTIVE

To analyse the time to onset of intussusception in a large series of PJS probands.

METHODS

STK11 mutation status was evaluated in 225 PJS probands and medical histories of the patients reviewed.

RESULTS

135 (60%) of the probands possessed a germline STK11 mutation; 109 (48%) probands had a history of intussusception at a median age of 15.0 years but with wide variability (range 3.7 to 45.4 years). Median time to onset of intussusception was not significantly different between those with identified mutations and those with no mutation detected, at 14.7 years and 16.4 years, respectively (log-rank test of difference, chi(2) = 0.58, with 1df; p = 0.45). Similarly no differences were observed between patient groups on the basis of the type or site of STK11 mutation.

CONCLUSIONS

The risk of intussusception in PJS is not influenced by STK11 mutation status.

An updated mutation spectrum in an Australian series of PJS patients provides further evidence for only one gene locus

The genetic predisposition Peutz-Jeghers Syndrome (PJS) has been shown to be associated with mutations in the serine threonine kinase 11 (STK11) gene but only a proportion of probands have been shown to harbour changes in the gene. The remaining patients were proposed to be either associated with a second PJS gene or they harboured more cryptic mutations within the STK11 gene itself. With the introduction of the multiplex ligation probe amplification (MLPA) assay, large sequence losses or gains can be more readily identified. In this report we have screened 33 PJS patients from unrelated families, employing a combination of denaturing high-performance liquid chromatography, direct DNA sequencing and the MLPA assay to identify deleterious changes in the STK11 gene. The results revealed that 24 (73%) of patients diagnosed with PJS-harboured pathogenic mutations in the STK11 gene, including 10 (36%) with exonic or whole-gene deletions. No phenotypic differences were identified in patients harbouring large deletions in the STK11 gene compared to patients harbouring missense or nonsense mutations. Mutation analysis in PJS should include techniques such as MLPA to identify large exonic or whole-gene deletions and rearrangements. The high proportion of families with identifiable mutations in the STK11 gene using this range of techniques suggests that most, if not all PJS, is attributable to mutations in the STK11 gene, perhaps including as yet undiscovered changes in promoter or enhancer sequences or other cryptic changes.

Frequency and spectrum of cancers in the Peutz-Jeghers syndrome

BACKGROUND

Although an increased cancer risk in Peutz-Jeghers syndrome is established, data on the spectrum of tumors associated with the disease and the influence of germ-line STK11/LKB1 (serine/threonine kinase) mutation status are limited.

EXPERIMENTAL DESIGN

We analyzed the incidence of cancer in 419 individuals with Peutz-Jeghers syndrome, and 297 had documented STK11/LKB1 mutations.

RESULTS

Ninety-six cancers were found among individuals with Peutz-Jeghers syndrome. The risk for developing cancer at ages 20, 30, 40, 50, 60, and 70 years was 2%, 5%, 17%, 31%, 60%, and 85%, respectively. The most common cancers represented in this analysis were gastrointestinal in origin, gastroesophageal, small bowel, colorectal, and pancreatic, and the risk for these cancers at ages 30, 40, 50, and 60 years was 1%, 9%, 15%, and 33%, respectively. In women with Peutz-Jeghers syndrome, the risk of breast cancer was substantially increased, being 8% and 31% at ages 40 and 60 years, respectively. Kaplan-Meier analysis showed that cancer risks were similar in Peutz-Jeghers syndrome patients with identified STK11/LKB1 mutations and those with no detectable mutation (log-rank test of difference chi2 = 0.62; 1 df; P = 0.43). Furthermore, the type or site of STK11/LKB1 mutation did not significantly influence cancer risk.

CONCLUSIONS

The results from our study provide quantitative information on the spectrum of cancers and risks of specific cancer types associated with Peutz-Jeghers syndrome.

LKB1 exonic and whole gene deletions are a common cause of Peutz-Jeghers syndrome

BACKGROUND

LKB1/STK11 germline mutations cause Peutz-Jeghers syndrome (PJS). The existence of a second PJS locus is controversial, the evidence in its favour being families unlinked to LKB1 and the low frequency of LKB1 mutations found using conventional methods in several studies. Exonic and whole gene deletion or duplication events cannot be detected by routine mutation screening methods.

OBJECTIVE

To seek evidence for LKB1 germline deletions or duplications by screening patients meeting clinical criteria for PJS but without detected mutations on conventional screening.

METHODS

From an original cohort of 76 patients, 48 were found to have a germline mutation by direct sequencing; the remaining 28 were examined using multiplex ligation dependent probe amplification (MLPA) analysis to detect LKB1 copy number changes.

RESULTS

Deletions were found in 11 of the 28 patients (39%)--that is, 14% of all PJS patients (11/76). Five patients had whole gene deletions, two had the promoter and exon 1 deleted, and in one patient exon 8 was deleted. Other deletions events involved: loss of exons 2-10; deletion of the promoter and exons 1-3; and loss of part of the promoter. No duplications were detected. Nine samples with deletions were sequenced at reported single nucleotide polymorphisms to exclude heterozygosity; homozygosity was found in all cases. No MLPA copy number changes were detected in 22 healthy individuals.

CONCLUSIONS

These results lessen the possibility of a second PJS locus, as the detection rate of germline mutations in PJS patients was about 80% (59/76). It is suggested that MLPA, or a suitable alternative, should be used for routine genetic testing of PJS patients in clinical practice.

A novel mutation of STK11/LKB1 gene leads to the loss of cell growth inhibition in head and neck squamous cell carcinoma

To investigate whether genetic alteration of the STK11 (serine/threonine kinase 11)/LKB1 tumor-suppressor gene is involved in the carcinogenesis of head and neck squamous cell carcinoma (HNSCC), the entire encoding exons and flanking intronic sequences of the STK11/LKB1 gene were analysed with direct genomic sequencing of 15 HNSCC specimens. A novel missense mutation with presumed loss of heterozygosity (LOH) and 10 polymorphisms were identified in these samples. The novel mutation of STK11/LKB1 at nucleotide position 613 G --> A, which causes the amino-acid substitution from alanine to threonine at residue 205 within the catalytic kinase domain, was identified in cell line RPMI 2650. To further determine whether this point mutation affects the gene function, constructs of the wild type and A205T mutant of the STK11/LKB1 gene expression vectors were created and transfected into RPMI 2650 cells. Our results showed that the reintroduction of the wild-type but not the mutant STK11/LKB1 construct into RPMI 2650 cells induced suppression of the cell growth. The mutation also affected the kinase activity of the Stk11/Lkb1 protein. This led us to conclude that the A205T point mutation of the STK11/LKB1 gene produces functionally inactive proteins. This is the first described mutation of the STK11/LKB1 gene in HNSCC. While the mutation frequency of the STK11/LKB1 gene in HNSCC remains to be determined in future studies, our data strongly suggests that STK11/LKB1 is involved in the carcinogenesis of HNSCC.

Nasal polyposis in Peutz-Jeghers syndrome: a distinct histopathological and molecular genetic entity

BACKGROUND

Peutz-Jeghers syndrome (PJS) is an autosomal dominant hamartomatous polyposis syndrome of the gastrointestinal tract, caused by a germline STK11/LKB1 mutation. Nasal polyposis was described in the original report by Peutz. Recently, a molecular-genetic association between nasal polyposis and PJS has been reported.

OBJECTIVE

To further explore the occurrence and pathogenesis of PJS-related nasal polyposis.

METHODS

51 patients with PJS, 84 unaffected family members and 36 spouses from 18 families with PJS were questioned for the presence of nasal polyposis. 12 PJS-related nasal polyps, 1 carcinoma of the nasal cavity and 28 sporadic nasal polyps were analysed for loss of (wild type) STK11/LKB1, eosinophilia, squamous metaplasia, dysplasia and expression of cyclo-oxygenase 2 and p53.

RESULTS

Nasal polyps occurred in 8 of 51 patients with PJS, and were not reported by non-affected family members (p<0.001). Germline STK11/LKB1 mutations were identified in all patients with PJS and nasal polyposis. Loss of heterozygosity was found in four of eight PJS-related nasal polyps, but not in sporadic nasal polyps (p = 0.002). PJS-related nasal polyps showed less eosinophilia than sporadic nasal polyps (p<0.001). Expression of cyclo-oxygenase 2 was found in 11 of 12 PJS-related nasal polyps and 19 of 28 sporadic nasal polyps (p>0.05). Overexpression of p53 was not found.

CONCLUSIONS

Nasal polyposis occurs in a significant number of Dutch patients with PJS, one of whom developed a carcinoma in the nasal cavity. The loss of heterozygosity, and the absence of eosinophilia suggest a distinct pathogenesis compared with sporadic nasal polyposis.

High proportion of large genomic STK11 deletions in Peutz-Jeghers syndrome

Germline mutations in the STK11 gene have been identified in 10-70% of patients with Peutz-Jeghers syndrome (PJS), an autosomal-dominant hamartomatous polyposis syndrome. A second locus was assumed in a large proportion of PJS patients. To date, STK11 alterations comprise mainly point mutations; only a small number of large deletions have been reported. We performed a mutation analysis for the STK11 gene in 71 patients. Of these, 56 met the clinical criteria for PJS and 12 were presumed to have PJS because of mucocutaneous pigmentation only or bowel problems due to isolated PJS polyps. No clinical information was available for the remaining three patients. By direct sequencing of the coding region of the STK11 gene, we identified point mutations in 37 of 71 patients (52%). We examined the remaining 34 patients by means of the multiplex ligation-dependent probe amplification (MLPA) method, and detected deletions in 17 patients. In four patients the deletion extended over all 10 exons, and in eight patients only the promoter region and exon 1 were deleted. The remaining deletions encompassed exons 2-10 (in two patients), exons 2-3, exons 4-5, or exon 8. When only patients who met the clinical criteria for PJS are considered, the overall mutation detection rate increases to 94% (64% point mutations and 30% large deletions). No mutation was identified in any of the 12 presumed cases. In conclusion, we found that approximately one-third of the patients who met the clinical PJS criteria exhibited large genomic deletions that were readily detectable by MLPA. Screening for point mutations and large deletions by direct sequencing or MLPA, respectively, increased the mutation detection rate in the STK11 gene up to 94%. There may be still other mutations in the STK11 gene that are not detectable by the methods applied here. Therefore, it is questionable whether a second PJS locus exists at all.

A de novoMLH1 germ line mutation in a 31-year-old colorectal cancer patient

Hereditary nonpolyposis colorectal cancer is an autosomal dominant cancer predisposition syndrome caused by inherited germ line mutations in DNA mismatch repair genes, predominantly MSH2 and MLH1. Here we report the first proven de novo germ line mutation in MLH1 (c.666dupA) identified in a 31-year-old colorectal cancer patient with the alteration being present in a heterozygous state in all three germ layers and homozygously in his colon cancer. The mutation was absent in both biological parents and all sibs available. Despite extensive polymorphic marker analysis, the parental origin of c.666dupA could not be conclusively determined, representing either a single mutational event in a parental germ cell or (maternal) gonadal mosaicism. Although rare, consequential application of the Bethesda guidelines for genetic testing should allow the clinician to readily identify colorectal cancer patients below age 50 years who carry de novo mismatch repair gene mutations.

Mutations in the humanLKB1/STK11gene

The human LKB gene (official HUGO symbol, STK11) encodes a serine/threonine protein kinase that is defective in patients with Peutz-Jeghers syndrome (PJS). PJS is an autosomal dominantly inherited syndrome characterized by hamartomatous polyposis of the gastrointestinal tract and mucocutaneous pigmentation. To date, 145 different germline LKB1 mutations have been reported. The majority of the mutations lead to a truncated protein product. One mutational hotspot has been observed. A 1-bp deletion and a 1-bp insertion at the mononucleotide repeat (C6 repeat, c.837-c.842) between the codons 279-281 have been found in six and seven unrelated PJS families, respectively. However, these mutations account only for approximately 7% of all mutations identified in the PJS families (13/193). A review of the literature provides a total of 40 different somatic LKB1 mutations in 41 sporadic tumors and seven cancer cell lines. Mutations occur particularly in lung and colorectal cancer. Most of the somatic LKB1 mutations result in truncation of the protein. A mutational hotspot seems to be a C6 repeat accounting for 12.5% of all somatic mutations (6/48). These results are concordant with the germline mutation spectrum. However, the proportion of the missense mutations seems to be higher among the somatic mutations (45%) than among the germline mutations (21%), and only seven of the mutations are exactly the same in both of the mutation types.

Sequence changes in predicted promoter elements of STK11/LKB1 are unlikely to contribute to Peutz-Jeghers syndrome

Background

Germline mutations or large-scale deletions in the coding region and splice sites of STK11/LKB1 do not account for all cases of Peutz-Jeghers syndrome (PJS). It is conceivable that, on the basis of data from other diseases, inherited variation in promoter elements of STK11/LKB1 may cause PJS.

Results

Phylogenetic foot printing and transcription factor binding site prediction of sequence 5' to the coding sequence of STK11/LKB1 was performed to identify non-coding sequences of DNA indicative of regulatory elements. A series of 33 PJS cases in whom no mutation in STK11/LKB1 could be identified were screened for sequence changes in the putative promoter defined by nucleotides -1090 to -1472. Two novel sequence changes were identified, but were found to be present in healthy individuals.

Conclusion

These findings indicate that promoter sequence changes are unlikely to contribute to PJS.

De novo germline mutation in the serine-threonine kinase STK11/LKB1 gene associated with Peutz-Jeghers syndrome

Peutz-Jeghers syndrome (PJS) is an autosomal dominant disease, characterized phenotypically by mucocutaneous pigmentation and hamartomatous polyposis. Affected patients are at an increased risk of developing gastrointestinal and other malignancies. Mutations in the STK11/LKB1 (LKB1) gene, which encodes for a serine-threonine kinase, have been identified as a genetic cause of PJS. Molecular analysis of the LKB1 gene in a simplex case of PJS revealed a substitution of cytosine (C) for guanine (G) at codon 246 in exon 6, resulting in the Tyr246X mutation. The nucleotide substitution leads to a premature stop codon at the 246 residue, predicting a truncated protein and presumed loss of kinase activity. Analysis of DNA from both parents of the PJS patient did not show this mutation, which is therefore a de novo mutation. We isolated DNA from microdissected gastrointestinal hamartomatous polyps in the PJS patient and investigated the loss of heterozygosity (LOH) at the LKB1 locus by real-time fluorescence polymerase chain reaction genotyping using a fluorescent resonance energy transfer technique. The results suggest a different mechanism from LOH in the formation of hamartomatous polyps.

Genetic alterations in hereditary breast cancer

Genetic linkage studies have led to the identification of highly penetrant genes as the possible cause of inherited cancer risk in many cancer-prone families. Most women with a family history of breast/ovarian cancer have tumors characterized by alterations in particular genes, mainly BRCA1 and BRCA2, but also CHK2, ATM, STK11 and others. This paper examines the BRCA1 and BRCA2 genes, focusing on the Italian pattern of mutations. The function of these two genes, classified as tumor suppressors, is linked with key metabolic mechanisms such as DNA damage repair, regulation of gene expression and cell cycle control. The pathological BRCA allelic variants may cause alteration of protein function, transcriptional activity and DNA repair; accumulation of the defects leads to widespread chromosome instability that may be directly responsible for cancer formation. In fact, mutations in BRCA1 and BRCA2, conferring a highly increased susceptibility to breast and ovarian cancer, do not lead to cancer by themselves. The current consensus is that these are 'caretaker' genes, which, when inactivated, allow other genetic defects to accumulate. The nature of these other molecular events may define the pathway through which BRCA1 and BRCA2 act. The BRCA mutation spectrum is complex, and the significance of most nucleotide alterations is difficult to understand. Moreover, the mutation pattern seems to be related to ethnicity. The Italian Consortium of Hereditary Breast and Ovarian Cancer has reviewed 1758 families; 23% have been found to be carriers of pathogenetic mutations in BRCA1 or BRCA2. Founder mutations have been described in geographically restricted areas of Italy; a regional founder effect has been demonstrated in Italy for the mutations BRCA1 5083del19 and BRCA2 8765delAG, and a probable new founder mutation has been characterized in Tuscany. The presence of founder mutations has practical implications for genetic testing.

Correlation of staining for LKB1 and COX-2 in hamartomatous polyps and carcinomas from patients with Peutz-Jeghers syndrome

Germline mutations of the LKB1 gene lead to Peutz-Jeghers syndrome (PJS), which is associated with a predisposition to gastrointestinal polyposis and cancer. In this study we tested for germline mutations of LKB1 in 11 patients with PJS from nine families and analyzed the expression patterns of the LKB1 and cyclo-oxygenase-2 (COX-2) proteins in 28 Peutz-Jeghers polyps (PJPs) and five carcinomas from these patients by immunohistochemical (IHC) analysis. In eight of those families we identified seven different mutations, which consisted of two splice site mutations, two nonsense mutations, one small in-frame deletion, one frame-shift mutation, and one silent mutation. Immunostaining revealed nuclear and cytoplasmic expression of LKB1 protein in 23 PJPs and five carcinomas, nuclear expression alone in one PJP, and loss of LKB1 protein expression in four PJPs, indicating a heterogeneous LKB1 expression pattern in PJPs. Overexpression of COX-2 was detected in 23 (82%) of 28 PJPs and in all carcinomas. Despite heterogeneity in staining of LKB1 among individuals and even among samples from the same individual, we found statistically significant correlations in staining of LKB1 relative to COX-2. These results suggest that COX-2 plays a role in tumorigenesis in PJS and may therefore be considered as a potential target for PJS chemoprevention.

Mapping of a translocation breakpoint in a Peutz-Jeghers hamartoma to the putative PJS locus at 19q13.4 and mutation analysis of candidate genes in polyp andSTK11-negative PJS cases

Germ-line mutations in the serine-threonine kinase gene STK11 (LKB1) cause Peutz-Jeghers syndrome (PJS), a rare autosomal dominantly inherited disease, characterized by hamartomatous polyposis and mucocutaneous pigmentation. STK11 mutations only account for about half of PJS cases, and a second disease locus has been proposed at chromosome segment 19q13.4 on the basis of genetic linkage analysis in one family. We identified a t(11;19)(q13;q13.4) in a PJS polyp arising from the small bowel in a female infant age 6 days. Because the breakpoint in 19q13.4 may disrupt the putative PJS disease gene mapping to this region, we mapped the breakpoint and analyzed DNA from the case and a series of STK11-negative PJS cases. Using two-color interphase fluorescence in situ hybridization, the breakpoint region was refined to a 0.5-Mb region within 19q13.4. Eight candidate genes mapping to the breakpoint region--U2AF2, EPN1, NALP4, NALP11, NALP5, ZNF444, PTPRH, and KIAA1811--were screened for mutations in germ-line and polyp DNA from the case and from 15 PJS cases that did not harbor germ-line STK11 mutations. No pathogenic mutations in the candidate genes were identified. This report provides further evidence of the existence of a second PJS disease locus at 19q13.4 and excludes involvement of eight candidate genes.

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Further observations on LKB1/STK11 status and cancer risk in Peutz-Jeghers syndrome

Germline mutations in the LKB1/STK11 tumour suppressor gene cause Peutz-Jeghers syndrome (PJS), a rare dominant disorder. In addition to typical hamartomatous gastrointestinal polyps and pigmented perioral lesions, PJS is associated with an increased risk of tumours at multiple sites. Follow-up information on carriers is limited and genetic heterogeneity makes counselling and management in PJS difficult. Here we report the analysis of the LKB1/STK11 locus in a series of 33 PJS families, and estimation of cancer risks in carriers and noncarriers. Germline mutations of LKB1/STK11 were identified in 52% of cases. This observation reinforces the hypothesis of a second PJS locus. In carriers of LKB1/STK11 mutations, the risk of cancer was markedly elevated. The risk of developing any cancer in carriers by age 65 years was 47% (95% CI: 27-73%) with elevated risks of both gastrointestinal and breast cancer. PJS with germline mutations in LKB1/STK11 are at a very high relative and absolute risk of multiple gastrointestinal and nongastrointestinal cancers. To obtain precise estimates of risk associated with PJS requires further studies of genotype-phenotype especially with respect to LKB1/STK11 negative cases, as this group is likely to be heterogeneous.

LKB1, a protein kinase regulating cell proliferation and polarity

LKB1 is a serine-threonine protein kinase mutated in patients with an autosomal dominantly inherited cancer syndrome predisposing to multiple benign and malignant tumours, termed Peutz-Jeghers syndrome. Since its discovery in 1998, much research has focused on identification and characterisation of its cellular roles and analysing how LKB1 might be regulated. In this review we discuss exciting recent advances indicating that LKB1 functions as a tumour suppressor perhaps by controlling cell polarity. We also outline the current understanding of the molecular mechanisms by which LKB1 is regulated in vivo, through interaction with other proteins as well as by protein phosphorylation and prenylation.

Genetic testing for high-risk colon cancer patients

Colorectal cancer is the third leading cause of cancer-related deaths in both men and women in the United States and is estimated to have affected 148,000 people in 2002. The cumulative lifetime risk for colon cancer is approximately 5%-6%, and this risk is influenced by hereditary and lifestyle factors. In fact, 20%-30% of all colon cancer cases have a potentially definable inherited cause, and 3%-5% of colon cancers occur in genetically defined high-risk colon cancer family syndromes. Although the genes responsible for the cases of moderate-risk colon cancer remain to be characterized, many of the genes responsible for the high-risk colon cancer cases have already been determined. These genetic discoveries have been translated into clinical practice and have led to improved risk assessment through the use of genetic testing. The introduction into clinical practice of genetic testing for the assessment of colon cancer risk has led to more effective management strategies for patients with potentially high-risk colon cancer and has presented new challenges to the clinician because of the unique issues involved with genetic testing. In this review, an overview of the colon cancer high-risk syndromes, with a focus on the availability and indications for genetic testing, is presented.

Search for the second Peutz-Jeghers syndrome locus: exclusion of the STK13, PRKCG, KLK10, and PSCD2 genes on chromosome 19 and the STK11IP gene on chromosome 2

Pathogenic mutations in the serine/threonine kinase STK11 (alias LKB1) cause Peutz-Jeghers syndrome (PJS) in most affected individuals. However, in a considerable number of PJS-patients mutations cannot be detected in STK11 suggesting genetic heterogeneity. One PJS family without STK11 mutations (PJS07) has previously been described with significant evidence for linkage to a second potential PJS locus on 19q13.3-->q13.4. In this study we investigated candidate genes within markers D19S180 and D19S254, since multipoint linkage analysis yielded significant LOD scores for this region in this family. Four genes in the region (cytohesin 2: PSCD2, kallikrein 10: KLK10, protein kinase C gamma: PRKCG, and serine/threonine kinase 13: STK13) potentially involved in growth inhibitory pathways or in the pathophysiology of can- cer, were considered as candidates. We first determined the genomic structure of the PSCD2 and PRKCG genes, and performed mutation analysis of all exons and exon-intron junctions of the four genes, in the PJS07 family. No pathogenic mutation was identified in these four genes in affected individuals. A very rare polymorphism resulting in a conserved amino acid change Lys to Arg was found in PSCD2. These data provide considerable evidence for exclusion of these four genes as candidates for the second locus on 19q13.3-->q13.4 in PJS. Finally, we also excluded the recently identified STK11-interacting protein gene (STK11IP, alias LIP1) mapped in 2q36 as candidate for PJS in the PJS07 family, although this could be a good candidate in other non-STK11/LKB1 families.

Mutation analysis of the STK11/LKB1 gene and clinical characteristics of an Australian series of Peutz-Jeghers syndrome patients

Peutz-Jeghers syndrome (PJS) is a rare cancer predisposition, which is characterized by the presence of hamartomatous polyposis and mucocutaneous pigmentation. A significant proportion of both familial and sporadic forms of this disorder are associated with mutations in the STK11 (serine/threonine kinase 11)/LKB1 gene. In this report we present a series of Australian PJS cases, which suggest that mutations in the STK11 gene do not account for many families or patients without a family history. The most likely explanation is either the presence of another susceptibility gene or genetic mosaicism in the non-familial patients.

Genetics of Peutz-Jeghers syndrome, Carney complex and other familial lentiginoses

Peutz-Jeghers syndrome (PJS, #175200) and Carney complex (CNC, OMIM#160980) are the two most common multiple neoplasia syndromes associated with lentiginosis. Both disorders are inherited in an autosomal dominant manner and they have recently been elucidated at the molecular level. PJS and CNC share manifestations with Cowden syndrome (or Cowden disease) (CS, OMIM#158350) and Bannayan-Riley-Ruvalcaba syndrome (BRR, OMIM#153480). The endocrine tumors of CS and PJS, which could classify these disorders as variant types of multiple endocrine neoplasias (MENs), are not present in most CS and BRR patients, but lentigines are shared by PJS, CNC and BRR. The serine-threonine kinase STK11 (or LKB1), located on 19p13, is mutated in more than half of all PJS kindreds. The R1alpha subunit of c-AMP-dependent protein kinase A, located on 17q22-24, is mutated in 40% of CNC kindreds. The protein phosphatase PTEN is mutated in most cases of CS and in almost 50% of BRR kindreds, despite significant clinical heterogeneity in these syndromes. The molecular elucidation of the lentiginoses and their related syndromes identifies new pathways of growth control and cellular regulation that are important for endocrine signaling, tumorigenesis, cutaneous function and embryonic development.

Small intestinal neoplasms

Small intestinal neoplasms are uncommonly encountered in clinical practice. They may occur sporadically, in association with genetic diseases (e.g., familial adenomatous polyposis coli or Peutz-Jeghers syndrome), or in association with chronic intestinal inflammatory disorders (e.g., Crohn's disease or celiac sprue). Benign small intestinal tumors (e.g., leiomyoma, lipoma, hamartoma, or desmoid tumor) usually are asymptomatic but may present with intussusception. Primary malignancies of the small intestine-including adenocarcinoma, leiomyosarcoma, carcinoid, and lymphoma-may present with intestinal obstruction, jaundice, bleeding, or pain. Extraintestinal neoplasms may involve the intestine via contiguous spread or peritoneal metastasis. Hematogenous metastases to the intestine from an extraintestinal primary are unusual and are most typical of melanoma. Because the small intestine is relatively inaccessible to routine endoscopy, diagnosis of small intestinal neoplasms is often delayed for months after onset of symptoms. When the diagnosis is suspected, enteroclysis is the most useful imaging study. Small bowel endoscopy (enteroscopy) is increasingly widely available and may permit earlier, nonoperative diagnosis.

Gene for the human transmembrane-type protein tyrosine phosphatase H (PTPRH): genomic structure, fine-mapping and its exclusion as a candidate for Peutz-Jeghers syndrome

Mutations in the serine/threonine kinase STK11 lead to Peutz-Jeghers syndrome (PJS) in a subset of affected individuals. Significant evidence for linkage to a second potential PJS disease locus on 19q13.4 has previously been described in one PJS family (PJS07). In the current study, we investigated this second locus for PJS gene candidates. We mapped the main candidate gene in this region, the gene for the transmembrane-type protein tyrosine phosphatase H (PTPRH), within 15 kb telomeric to the marker D19S880. We determined its genomic structure, and performed mutation analysis of all exons and the exon-intron junctions of the PTPRH gene in the PJS07 family. No disease causing mutation was identified in PTPRH in affected individuals, suggesting the existence of an as yet not identified gene on 19q13.4 as a second PJS gene.