Large deletions and splicing‐site mutations in the STK11 gene in Peutz‐Jeghers Chilean families

Peutz‐Jeghers syndrome (PJS) is an autosomal dominant disorder characterized by mucocutaneous melanocytic macules, gastrointestinal hamartomatous polyposis and an increased risk of various neoplasms. Germline mutations in the serine/threonine kinase 11 (STK11) gene have been identified as a cause for PJS. The aim of this study was to characterize the genotype of Chilean PJS patients. Mutation screening of 13 patients from eight PJS families was performed using a single strand conformation polymorphism analysis, DNA sequencing and multiplex ligation‐dependent probe amplification assay. The breakpoints of the genomic rearrangements were assessed by a long‐range polymerase chain reaction and sequencing. The results revealed the existence of seven different pathogenic mutations in STK11 gene in seven unrelated families, including three point mutations and four large genomic deletions. Three of these point mutations (43%, 3/7) may be considered as novel. Our results showed that a germline mutation is present in STK11 in 88% of probands fulfilling the diagnostic criteria of PJS. In this study, the combination of two different experimental approaches in the screening of the STK11 in PJS, led to a higher percentage of mutation detection.     

Mutations in the human LKB1/STK11 gene

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.     

A novel STK11 germline mutation in two siblings with Peutz-Jeghers syndrome complicated by primary gastric cancer

Patients with Peutz-Jeghers syndrome (PJS) are known to be at risk of gastric cancer (GC), and the STK11 gene is a susceptibility gene for PJS. However, as no cases of PJS with GC in which a STK11 germline mutation has been identified have ever been reported and other susceptibility genes have also been suggested to be involved in PJS, the relation between STK11 germline mutations and GC in PJS is still unknown. In this study, we used sequencing analysis to investigate the STK11, CDH1, and TP53 loci for a germline mutation in two siblings with PJS with primary GC. A novel type of the STK11 germline mutation, c.890delG, encoding a truncated protein (p.Arg297fsX38) was identified, but no germline mutations of the CDH1 and TP53 genes were detected. No inactivation of the wild-type allele by somatic mutation or chromosomal deletion or hypermethylation at the 5'-CpG site of STK11 was detected in the GC. This is the first report of a STK11 germline mutation in a PJS patient with GC and should contribute to establishing correlations between the STK11 germline mutations and GC in PJS patients.     

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.     

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.     

Functional analysis of LKB1/STK11 mutants and two aberrant isoforms found in Peutz-Jeghers Syndrome patients

Peutz-Jeghers Syndrome (PJS) is thought to be caused by mutations occurring in the widely expressed serine/threonine protein kinase named LKB1/STK11. Recent work has led to the identification of four mutants (R304W, I177N, K175-D176del, L263fsX286) and two novel aberrant LKB1/STK11 cDNA isoforms (r291-464del, r485-1283del) in a group of PJS Italian patients. Three of the four mutations only change 1 or 2 amino acids in the LKB1/STK11 catalytic domain. Here we demonstrate that all six LKB1/STK11 variants analysed are completely inactive in vitro as they were unable to autophosphorylate at Thr336, the major LKB1/STK11 autophosphorylation site, and to phosphorylate the p53 tumour suppressor protein. We also show that 5 out of the 6 variants are entirely localised in the nucleus in contrast to the wild type LKB1/STK11, which is detected in both the nucleus and cytoplasm. Finally we demonstrate that all 6 LKB1/STK11 variants, in contrast to wild type LKB1/STK11, are unable to suppress the growth of melanoma G361 cells. Taken together, these results demonstrate that the LKB1 mutations investigated in this study lead to the loss of serine/threonine kinase activity and are therefore likely to be the primary cause of PJS development in the patients that they were isolated from.     

High frequency of large genomic deletions in the PCCA gene causing propionic acidemia

Mutations in either the PCCA or PCCB genes are responsible for propionic acidemia (PA), one of the most frequent organic acidemias inherited in autosomal recessive fashion. Most of the mutations detected to date in both genes are missense. In the case of PCCA deficient patients, a high number of alleles remain uncharacterized, some of them suspected to carry an exonic deletion. We have now employed multiplex ligation probe amplification (MLPA) and long-PCR in some cases to screen for genomic rearrangements in the PCCA gene in 20 patients in whom standard mutation detection techniques had failed to complete genotype analysis. Eight different deletions were found, corresponding to a frequency of 21.3% of the total PCCA alleles genotyped at our center. Two of the exonic deletions were frequent, one involving exons 3–4 and another exon 23 although in the first case two different chromosomal breakpoints were identified. Absence of exons 3 and 4 which is also the consequence of the novel splicing mutation c.231 + 1g > c present in two patients, presumably results in an in-frame deletion covering 39 aminoacids, which was expressed in a eukaryotic system confirming its pathogenicity. This work describes for the first time the high frequency of large genomic deletions in the PCCA gene, which could be due to the characteristics of the PCCA gene structure and its abundance in intronic repetitive elements. Our data underscore the need of using gene dosage analysis to complement routine genetic analysis in PCCA patients.     

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

The Peutz‐Jeghers syndrome (PJS) is a rare hereditary disorder in which gastrointestinal hamartomatous polyposis, mucocutaneous pigmentation, and a predisposition for developing cancer are transmitted in an autosomal dominant fashion. The recently identified LKB1/STK11 gene located at chromosome 19p13.3 is mutated in a number of PJS pedigrees. We performed mutation analysis in 19, predominantly Dutch, PJS families. In 12 of these families, we identified LKB1/STK11 mutations, none of which has been described before. These 12 novel LKB1/STK11 mutations consist of one nonsense mutation, three frameshift deletions, three frameshift insertions, two acceptor splice site mutations, and three missense mutations. In addition, we detected four polymorphisms in LKB1/STK11. In the remaining seven PJS families, we found no apparent abnormalities of the LKB1/STK11 gene, which could reflect the existence of locus heterogeneity in PJS. None of the mutations occurred in more than one family, and a number were demonstrated to have arisen de novo. The diverse array of mutations found, the apparent high mutation rate, as well as the existence of a possible second PJS locus, renders diagnostic or predictive genetic testing in individual patients difficult, although future identification of additional mutations or even gene(s) will help in increasing the yield of direct mutation analysis. Hum Mutat 13:476–481, 1999. © 1999 Wiley‐Liss, Inc.     

Germline mutations of the LKB1 (STK11) gene in Peutz-Jeghers patients

Germline mutations of the LKB1 (STK11) serine/threonine kinase gene (chromosome 19p13.3) cause Peutz-Jeghers syndrome, which is characterised by hamartomas of the gastrointestinal tract and typical pigmentation. Peutz-Jeghers syndrome carries an overall risk of cancer that may be up to 20 times that of the general population. Here, we report the results of a screen for germline LKB1 mutations by DNA sequencing in 12 Peutz-Jeghers patients (three sporadic and nine familial cases). Mutations were found in seven (58%) cases, in exons 1, 2, 4, 6, and 9. Five of these mutations, two of which are identical, are predicted to lead to a truncated protein (three frameshifts, two nonsense changes). A further mutation is an in frame deletion of 6 bp, resulting in a deletion of lysine and asparagine; the second of these amino acids is conserved between species. The seventh mutation is a missense change in exon 2, converting lysine to arginine, affecting non-conserved amino acids and of uncertain functional significance. Despite the fact that Peutz-Jeghers syndrome is usually an early onset disease with characteristic clinical features, predictive and diagnostic testing for LKB1 mutations will be useful for selected patients in both familial and non-familial contexts.     

Peutz-Jeghers syndrome with osseous metaplasia of the intestinal polyps

A cam of Peutz-Jeghers syndrome (PJS) with osseous metaplasia In three of 15 hamartomatous polyps of the small Intestine Is reported. At 35 years of age, the patient was diagnosed as having PJS by cutaneous pigmentation around the mouth and polyposis of the stomach, duodenum and Intestine. Fifty-two polyps of the large intestine were resected, which were Characteristic of those of PJS. Three of them showed adenomatous and carcinomatous changes, but there was no osseous metaplasia in any of the resected polyps. At age 40, he had surgery under the diagnosis of Intestinal obstruction. There were 15 polyps in the resected jejunum. These polyps were also characteristic of those of PJS. Additionally, three of these polyps were accompanied by osseous metaplasia. Histologically, mature bone formation and Calcification were found close to the hyperplastic glands In the submucosa or in the propriate muscle. Malignant transformation was not observed. Osseous metaplasia is extremely rare in benign potyps, and it has not been reported in hamartomatous polyps of PJS to date. The knowledge of this association may be helpful in the clinical diagnosis of this benign lesion in PJS.     

Identification of a novel STK11 gene mutation in a family affected with hereditary Peutz-Jeghers syndromeCSCD

Objective: To explore the genetic basis for a family affected with Peutz-Jeghers syndrome (PJS). Methods: Genomic DNA was extracted from peripheral blood and oral swab samples from the patient and her relatives. Next-generation sequencing (NGS) was used to analyze 106 target genes by capturing the exons and adjacent intronic regions. Suspected pathogenic mutation was verified by NGS. Results: A missense STK11 mutation was detected in the proband, which was not reported previously. The mutation has caused substitution of Leucine by Proline. NGS has detected the same mutation in the mother but not among other relatives. Conclusion: This hereditary case of PJS may be attributed to the missense mutation of the STK11 gene. © 2018 West China University of Medical Sciences. All rights reserved.     

STK_(11)基因突变在中国人Peutz-Jeghers综合征中的特征

目的　明确 STK1 1 基因在中国人 Peutz- Jeghers(PJ)综合征的突变特征 ,为建立基因诊断奠定基础。方法　用 DNA直接测序方法 ,对 18个家系的 PJ综合征患者 STK1 1 基因 9个外显子进行研究。结果　在 6个家系中发现 6个使基因产物发生改变的突变 ,推测最终导致产生截短型蛋白。结论　在中国人PJ综合征患者中 STK1 1 基因突变的检出率为 6 /18。突变位点比较广泛 ,2 /3集中在第 1外显子。两代以上发病的家系突变率为 6 6 .7% ,散发病例突变率为 16 .7     

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.     

High incidence of large deletions in the PMS2 gene in Spanish Lynch syndrome families

Lynch syndrome (LS) is caused by germline mutations in one of the four mismatch repair (MMR) genes. Defects in this pathway lead to microsatellite instability (MSI) in DNA tumors, which constitutes the molecular hallmark of this disease. Selection of patients for genetic testing in LS is usually based on fulfillment of diagnostic clinical criteria (i.e. Amsterdam criteria or the revised Bethesda guidelines). However, following these criteria PMS2 mutations have probably been underestimated as their penetrances appear to be lower than those of the other MMR genes. The use of universal MMR study‐based strategies, using MSI testing and immunohistochemical (IHC) staining, is being one proposed alternative. Besides, germline mutation detection in PMS2 is complicated by the presence of highly homologous pseudogenes. Nevertheless, specific amplification of PMS2 by long‐range polymerase chain reaction (PCR) and the improvement of the analysis of large deletions/duplications by multiplex ligation‐dependent probe amplification (MLPA) overcome this difficulty. By using both approaches, we analyzed 19 PMS2‐suspected carriers who have been selected by clinical or universal strategies and found five large deletions and one frameshift mutation in PMS2 in six patients (31%). Owing to the high incidence of large deletions found in our cohort, we recommend MLPA analysis as the first‐line method for searching germline mutations in PMS2.     

Prevalence of 22q11 region deletions in patients with velopharyngeal insufficiency

Velo-cardio-facial syndrome, DiGeorge syndrome, conotruncal anomaly face syndrome, tetralogy of Fallot, and pulmonary atresia with ventricular septal defect are all associated with hemizygosity of 22q11. While the prevalence of the deletions in these phenotypes has been studied, the frequency of deletions in patients presenting with velopharyngeal insufficiency (VPI) is unknown. We performed fluorescence in situ hybridization for locus D22S75 within the 22q11 region on 23 patients with VPI (age range 5–42 years) followed in the Craniofacial Clinic at the University of Florida. The VPI occurred either as a condition of unknown cause (n=16) or as a condition remaining following primary cleft palate surgery (n=7). Six of sixteen patients with VPI of unknown cause and one of seven with VPI following surgery had a deletion in the region. This study documents a high frequency of 22q11 deletions in those presenting with VPI unrelated to overt cleft palate surgery and suggests that deletion testing should be considered in patients with VPI. Am. J. Med. Genet. 77:8–11, 1998. © 1998 Wiley-Liss, Inc.     

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.     

Survival,surveillance, and genetics in patients with Peutz–Jeghers syndrome: A nationwide study

Peutz–Jeghers syndrome (PJS) is an autosomal dominant hereditary polyposis syndrome causing increased morbidity and mortality due to complications of polyposis and the development of cancer. STK11 is the only gene known to be associated with PJS, although in 10%–15% of patients fulfilling the diagnostic criteria no pathogenic variant (PV) is identified. The primary aim of this study was to identify the genetic etiology in all known PJS patients in Denmark and to estimate the risk of cancer, effect of surveillance and overall survival. We identified 56 patients (2–83 years old) with PJS. The detection rate of PVs was 96%, including three cases of mosaicism (6%). In two patients a variant was not detected. At the age of 40 years, the probabilities of cancer and death were 21% and 16%, respectively; at the age of 70 years these probabilities were 71% and 69%. Most cases of cancer (92%) were identified between the scheduled examinations in the surveillance program. These observations emphasize that PJS should be regarded as a general cancer predisposition syndrome, where improvement of clinical care is needed.     

STK11/LKB1 germline mutations are not identified in most Peutz–Jeghers syndrome patients

Germline mutations of the STK11 gene mapped to chromosome 19p13.3 are responsible for Peutz Jeghers syndrome (PJS), a dominant disorder associated with characteristic gastrointestinal hamartomatous polyps and a predisposition to various cancers. We conducted a detailed investigation of germline STK11 alterations by protein truncation test and genomic DNA sequence analysis in ten unrelated PJS families. We identified a novel truncating deletion spanning STK11 exons 2-7 in a single patient and several known polymorphisms. Loss of heterozygosity studies in PJS polyps of four of these patients identified an allelic deletion of D19S886 in another patient. Our results suggest that STK11 mutations account for only a proportion of PJS cases.