A novel mutation in the STK11 gene causes heritable Peutz-Jeghers syndrome - a case report
- Jing-Hui Chen†1,
- Jing-Jing Zheng†2,
- Qin Guo†3,
- Chao Liu†2, 4,
- Bin Luo2,
- Shuang-Bo Tang2,
- Jian-Ding Cheng2Email author and
- Er-Wen Huang2Email author
© The Author(s). 2017
Received: 19 September 2016
Accepted: 25 January 2017
Published: 23 February 2017
Peutz-Jeghers syndrome (PJS) is a rare disorder characterized by multiple gastrointestinal hamartomatous polyps and mucocutaneous pigmentation. STK11 has been identified as a causative gene for this disease.
Herein we report a Chinese Han kindred with PJS. Onset for the PJS signs in three of the patients was rarely as early as at birth. We identified a novel heterozygous mutation (c.440_441delGT, p.Arg147Leufs*15) in the gene STK11, causing a short frameshift followed by a deletion of 63% of the amino acids in the STK protein. This mutation co-segregated with the PJS phenotype, and was absent in two hundred of unrelated ethnicity-matched controls. The mutation led to expression decrease of unaffected STK11 protein in patients than in controls, as well in PJ polyps than in circulating leucocytes from the patients. Phosphorylation levels of the downstream kinase AMPKα altered according with the expression of STK11. These results indicated the possibility that haploinsufficiency and epigenetic reduction of STK11 contributed to the pathogenesis of the disease.
This study identifies a novel mutation in the pathogenic gene STK11 leading to PJS.
KeywordsFrameshift mutation Peutz-Jeghers syndrome STK11 Truncating mutation Case report
Peutz-Jeghers syndrome (PJS) is a rare disorder characterized by multiple gastrointestinal hamartomatous polyps and mucocutaneous pigmentation [1, 2]. The disorder appears without gender predominance and is discovered in various ethnic groups, at an incidence estimated to range from 1/50,000 to 1/200,000 . Clinical diagnosis of PJS can be made in a patient presenting one of the following signs: no less than two histologically confirmed PJ polyps, any number of PJ polyps with a family history of PJS, characteristic mucocutaneous pigmentation with a family PJS history, any number of PJ polyps associated with characteristic mucocutaneous pigmentation . Mucocutaneous pigmented lesions usually occur at the lips, nostrils, perianal area, or digits; PJ polyps usually occur in the gastrointestinal tract, especially frequently in the small intestine, but have been also reported in extra-gastrointestinal organs [5, 6]. The polyps can lead to complications including alimentary canal obstruction, rectal prolapse, intussusception and severe bleeding with secondary anemia . PJS increases the risk for various neoplasms, including gastrointestinal and extra-gastrointestinal, benign and malignant [8–10]. The serine/threonine kinase 11 coding gene (STK11) on chromosome 19p13.3 has been identified as a pathogenic gene of PJS [11, 12]. PJS signs usually appear within childhood or adolescent years [2, 3], and sometimes can also be firstly diagnosed in newborns or adults [13–15]. Here we report a Chinese Han family with PJS caused by a novel mutation (c.440_441delGT, p.Arg147Leufs*15) in the STK11 gene.
Clinical features of the affected family members
Died of neoplasm at forty
Age at onset for mucocutaneous pigmentation (years)
earlier than 2
present at birth
present at birth
present at birth
Order of onset for mucocutaneous pigmentation
lips first, then digits
lips first, then digits
lips first, then digits
lips first, then digits
Age at first diagnosis of PJ polyps (years)
Age at the first resection of polyps (years)
Position of PJ polyps
Antibody (ab79355) targeting site 332–336 in STK11 was purchased from Abcam (Cambridge, UK). AMPKα-targeting antibaody (#2532) was purchased from Cell Signaling Technology (Boston, USA). GAPDH-targeting antibody (AF0006), phospho-AMPKα (Thr172)-targeting antibody (AA393), horseradish peroxidase-conjugated goat anti-rabbit secondary antibody (A0208), horseradish peroxidase-conjugated goat anti-mouse secondary antibody (A0216) were all purchased from Beyotime (Nantong, Jiangsu, China).
DNA preparation and sequencing of the STK11 gene
Peripheral blood was collected in EDTA anticoagulant tubes. Genomic DNA was extracted from leukocytes using the Wizard Genomic DNA Purification Kit (Promega, Madison, WI, USA) according to the manufacturer’s instructions. 30 ng of DNA was used as PCR template to amplify the fragments of coding regions, 5′ and 3′ untranslated regions in STK11. Amplification products were Sanger sequenced using the ABI Genetic Analyzer (Applied Biosystems, Foster, CA, USA). The sequences of primers used for PCR and sequencing were listed in Additional file 1: Table S1.
Reverse transcription-polymerase chain reaction (RT-PCR) assay
Total RNA was extracted from leukocytes using the TRIzol reagent (Invitrogen, Carlsbad, CA, USA) according to the manufacturer’s protocol. RT-PCR assay was performed using the OneStep RT-PCR Kit (QIAGEN, Dusseldorf, Germany), according to the manufacturer’s protocol. RT-PCR primers were listed in Additional file 1: Table S2.
Protein extraction and western blot assay
Leukocytes isolated from circulating blood were lysed using RIPA lysis buffer (Beyotime, Nantong, Jiangsu, China) on ice. The lysis product was centrifuged at 12,000 × g for 10 min at 4 °C. The supernatant was collected for the following protein analysis. Tissue from the PJ polyps was cut into pieces and homogenized in RIPA lysis buffer (0.5 ml/100 mg tissue) for 10 min on ice. Then centrifuged as described above. Protein concentration was determined using the BCA reagent (Beyotime, Nantong, Jiangsu, China) according to the manufacturer’s instructions. The extracted proteins were isolated by SDS-PAGE electrophoresis in SDS-PAGE electrophoresis buffer (Beyotime, Nantong, Jiangsu, China) with 90 V voltage. The isolated proteins in SDS-PAGE gel were transfered onto polyvinylidene fluoride film in Western Transfer Buffer (Beyotime, Nantong, Jiangsu, China) with 200 mA current for 90 min. The polyvinylidene fluoride film with proteins was further treated as the following steps: incubated with 5% fat-free milk for 30 min and then with a primary antibody for 2 h at room temperature, washed to eliminate unspecific binding of the antibody, incubated with an horseradish peroxidase-conjugated secondary antibody for 1 h at room temperature, washed to eliminate unspecific binding of secondary antibody, incubated with BeyoECL chemiluminiscence reagent (Beyotime, Nantong, Jiangsu, China) according to the manufacturer’s instructions. Optical density representing the protein amount was captured and analyzed using the Luminescent Imaging Workstation (Tanon, Shanghai, China).
Hematoxylin-eosin staining of tissue slices
Paraffin-embedded polyp slices (5 μm of thick) were treated as the following steps: immersed in xylene for 3 × 2 min, dehydrated using alcohol at gradient concentrations (100%, 95%, 80%, 70%) for 5 × 2 min respectively, flushed with water for 3 min, incubated with Harris hematoxylin solution for 3 min, flushed with water for 3 min, incubated with 0.5% hydrochloric acid for 10 s, flushed with water for 15 min, incubated with alcohol (70%, 80% for 5 min respectively), incubated with 95% eosin-alcohol solution for 30 s, incubated with alcohol (95%, 100% for 5 min respectively), incubated with xylene-alcohol mixture (1:1) for 5 min, incubated with xylene for 5 min, sealed with neutral balsam and covered with coverslip.
To study the functional affection of the mutation, we investigated STK11 protein expression in circulating leukocytes, using an antibody that targets residues 332–336 in STK11 and consequently reacts with the wild-type but not affected STK11. As a result, expression of the wild-type STK11 in controls was significantly higher than that in the patients (p = 0.0019, Fig. 2c), suggesting that the disease might result from STK11 haploinsufficiency. Interestingly, we found the wild-type STK11 expressed less in the three PJ polyps from patient III-6 than in circulating leukocytes from the four patients (p = 0.0252, Fig. 2c), suggesting that epigenetic reduction of STK11 expression might be a second contribution to polyps formation. AMPKα has been reported to be phosphorylated at threonine 172 by STK11 [16, 17]. Here we also observed that the phosphorylation levels of AMPKα paralleled with the levels of STK11 expression (Fig. 2c).
PJS onset in most reported patients was within childhood or adolescent years and it was reported that the median time to onset for gastrointestinal symptoms was 13 years of age [2, 15]. In this study, the age of onset for pigmentation in three of the patients was as early as at birth, not firstly but relatively rarely reported. The onset heterogeneity of PJS in this family was not confirmed. There is no determined information about the PJS onset in two of the patients. But it can’t exclude the possibility that the disease onset in the two patients was also as early as at birth. The heterogeneity in polyps location in spite of the same mutation remains to be studied.
As a positive regulation, STK11 is released and shuttles from nucleus to cytoplasm, and interacts with STRADα/β and MO25α/β to stabilize the kinase activity [16, 18]. The entire kinase catalytic domain and amino acids 319–343 in STK11 are necessary for binding to STRAD . So it is self-evident that the mutant identified here is unable to associate with the STRADα/β-MO25α/β complex. Other interacting partners of STK11 have been successively identified and the indispensable motifs in STK11 for interacting with some of them have not yet been determined . So we can’t exclude the possibility that dominant negative effect is a third molecular mechanism by which the mutation results in PJS, if the inactive mutant occupies the partners.
There are hundreds of mutations in the STK11 gene reported to cause PJS. Here we identified a novel mutation which leads to a truncated STK11 protein, functionly causes inherited, even early-onset (remained to be further confirmed) PJS. Epigenetic expression reduction might be also one of the pathogenic mechanisms caused by the mutation. This study further expanded the mutation spectrum of PJS.
In conclusion, in this study we identified a novel heterozygous mutation (c.440_441delGT, p.Arg147Leufs*15) in the STK11 gene causing the inherited PJS in this family. Haploinsufficiency and epigenetic expression reduction of STK11 might contribute to the pathogenesis of the disease.
AMP-activated catalytic subunit alpha
Mouse protein 25 alpha/beta
Serine/threonine kinase 11
STE20-related kinase adaptor alpha/beta
We thank the subjects for their participation.
This work was supported by the National Natural Science Foundation (81302616) and the Natural Science Foundation of Guangdong Province China (2014A030313127).
Availability of data and material
The datasets used and analysed during the current study available from the corresponding author on reasonable request.
JHC and QG collected the samples. JJZ and EWH performed experiments. CL, JDC and EWH designed the study. BL and SBT revised the manuscript. EWH wrote the manuscript. All of the co-authors have read this manuscript and support this submission. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
Consent for publication
Written informed consents for publication of their clinical details and images were obtained from the adult patients, or from the guardians of the infant patients.
Ethics approval and consent to participate
This study was approved by the ethics committee of Sun Yat-Sen University and complied with the Declaration of Helsinki. All of the adult participants were informed to participate in this study with written consents. Children in the kindred participated in the study with written consents from their guardians.
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