Novel mutations in the STK11 gene in Thai patients with Peutz-Jeghers syndrome

Genetic variation at a splicing branch point in intron 7 of STK11: a rare variant decreasing its expression in a Chinese family with Peutz-Jeghers syndrome

BACKGROUND

Peutz-Jeghers syndrome (PJS), a rare dominantly inherited disease, is primarily characterized by hamartomatous polyps and melanotic macules as well as by an increased risk of cancer. The current study aimed to identify the pathogenic gene and pathogenic mechanism of a proband with PJS, thereby offering precise prevention and treatment strategies for PJS.

METHODS

A detailed clinical examination was performed of the proband diagnosed with PJS and her family members. In addition, peripheral venous blood was collected from the family members to extract genomic DNA. The pathogenic genes of the proband were identified using whole-exome sequencing, and the candidate pathogenic variants were verified via Sanger sequencing. Meanwhile, co-segregation tests were performed among six family members. Finally, reverse transcription-polymerase chain reaction (RT-PCR) was performed to assess transcript variants in the peripheral blood cells of patients and non-related healthy controls.

RESULTS

Genetic testing revealed a rare splicing variant c.921-1G > C in STK11 in the proband and in her sister and nephew, and the variant co-segregated among the affected family members and nonrelated healthy controls. The proband phenotypically presented with a rare gastric-type adenocarcinoma of the cervix. RT-PCR revealed that the STK11 c.921-1G > C variant could produce two transcripts. Of note, 40 base pairs were deleted in the aberrant transcript between exons 3 and 4, resulting in a frameshift variant and premature termination of the amino acid in exon 6 and ultimately leading to the loss of its functional domain in the STK11 protein. Finally, RT-PCR showed that compared with healthy controls, STK11 mRNA expression level was < 50% in patients.

CONCLUSION

The present study results indicated that the rare splicing variant c.921-1G > C in intron 7 of STK11 may be a pathogenic variant in patients with PJS. However, this variant (in intron 7) may not produce abnormal transcripts (deletion of 40 base pairs between exons 3 and 4), and PJS may be attributed to the decrease in STK11 expression. Therefore, this study emphasized the importance of genetic counseling, pre-symptomatic monitoring, and early complication management in PJS.

Genetic Screening and Analysis of LKB1 Gene in Chinese Patients with Peutz-Jeghers Syndrome

BACKGROUND Peutz-Jeghers syndrome (PJS) is an autosomal dominant genetic disease. It severely decreases patient quality of life and leads elevated cancer risk. Germline mutation of LKB1 is the leading cause of familial PJS. MATERIAL AND METHODS To characterize the germline mutation of LKB1 gene in Chinese familial and sporadic PJS patients, 14 PJS families, 5 sporadic PJS patients, and 250 healthy adults were collected and genomic DNAs of peripheral blood were extracted. Mutation screenings of LKB1 were performed using MLPA (multiplex ligation-dependent probe amplification), PCR, direct sequencing, and PCR-DHPLC (denaturing high-performance liquid chromatography). RESULTS A total of 12 kinds of germline mutations were found in 9 familial PJS patients, most of which were point mutations (7/12); 4 large deletions of LKB1 were also observed. Of the 12 mutations, 7 were pathogenic (2 were de novo), 4 were just polymorphisms, and 1 was indefinitely pathogenic. No pathogenic mutation in exons of the LKB1 gene was detected in the 5 sporadic PJS patients. The mutation detection rate for the LKB1 gene was 85.7% in our Chinese familial PJS and 63.2% in all Chinese PJS patients. Eight familial PJS patients were identified with pathogenic germline mutations in 14 unrelated families (57.1%). Further methylation detection and analysis showed promoter methylation in carcinomatous polyps. CONCLUSIONS LKB1 gene germline mutation with pathogenic effect is a common cause of familial PJS in Chinese patients; however, it is not the only molecular pathogen of PJS. Methylation in the LKB1 gene promoter region may cause carcinomatous change in intestinal polyps.

Clinical features, endoscopic polypectomy and STK11 gene mutation in a nine-month-old Peutz-Jeghers syndrome Chinese infant

AIM: To investigate multiple polyps in a Chinese Peutz-Jeghers syndrome (PJS) infant.

METHODS: A nine-month-old PJS infant was admitted to our hospital for recurrent prolapsed rectal polyps for one month. The clinical characteristics, a colonoscopic image, the pathological characteristics of the polyps and X-ray images of the intestinal perforation were obtained. Serine threonine-protein kinase 11 (STK11) gene analysis was also performed using a DNA sample from this infant.

RESULTS: Here we describe the youngest known Chinese infant with PJS. Five polyps, including a giant polyp of approximately 4 cm × 2 cm in size, were removed from the infant’s intestine. Laparotomy was performed to repair a perforation caused by pneumoperitoneum. The pathological results showed that this child had PJS. Molecular analysis of the STK11 gene further revealed a novel frameshift mutation (c.64_65het_delAT) in exon 1 in this PJS infant.

CONCLUSION: The appropriate treatment method for multiple polyps in an infant must be carefully considered. Our results also show that the STK11 gene mutation is the primary cause of PJS.

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.

One novel deletion and one splicing mutation of the LKB1 gene in two Chinese patients with Peutz-Jeghers syndrome

Peutz-Jeghers syndrome (PJS) is an uncommon autosomal dominant inherited disease, characterized by the occurrence of gastrointestinal hamartomatous polyps and pigmentation of the lips, buccal mucosa, and digits. Patients with PJS have a significant risk for developing tumors in multiple organs. Germline mutation of the LKB1 gene, which encodes a serine/threonine kinase that acts as a tumor suppressor, has been identified as a cause of PJS. The current study included two Chinese PJS probands and their available family members, as well as 200 unrelated healthy controls for comparison. Genomic DNA was extracted from the peripheral blood of these subjects. The nine coding exons and flanking introns of the LKB1 gene in the two probands and their family members were amplified by polymerase chain reaction (PCR) and then directly sequenced. Mutations identified in the patients were checked in the 200 healthy controls by PCR and denaturing high-performance liquid chromatography. Total RNA was extracted from the patient who was found to have a dubious splice site mutation and his available family members. Reverse transcription PCR was performed to identify the abnormal splicing caused by the splice site mutation. Two types of mutations were detected in the two PJS families. One type was a previously unreported 30-base-pair deletion in exon 4, and the other was an intron mutation that affected splicing. None of the 200 controls had either of these two types of mutations. The results provide support that mutation of the LKB1 gene is a cause of PJS, and expand the spectrum of LKB1 gene mutations.

Advances in the prevention, diagnosis and treatment of Peutz-Jeghers syndrome

Peutz-Jeghers syndrome (PJS) is an autosomal dominant inherited disease caused by inactivating germline mutations of the LKB1/STK11 gene and characterized by mucocutaneous pigmentation, multiple gastrointestinal hamartomatous polyps and family history. Life-threatening complications include intestinal obstruction and an increased risk for developing gastrointestinal malignancies and extraintestinal cancers. Surgery and endoscopic therapy are still main ways to manage gastrointestinal polyposis in PJS patients, and double-balloon enteroscopy has important clinical significance in the diagnosis and treatment of this disease. With the development of translational medicine, molecular targeted therapy (e.g., selective COX-2 inhibitors) brings a new approach to preventive treatment of gastrointestinal polyposis in PJS patients. Traditional Chinese medicine provides an alternative choice. In this paper, we review the recent advances in the prevention, diagnosis and treatment of PJS.

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.