Mutation-positive and mutation-negative patients with Cowden and Bannayan-Riley-Ruvalcaba syndromes associated with distinct 10q haplotypes

Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) encodes a tumor-suppressor phosphatase frequently mutated in both sporadic and heritable forms of human cancer. Germline mutations are associated with a number of heritable cancer syndromes that are jointly referred to as the "PTEN hamartoma tumor syndrome" (PHTS) and include Cowden syndrome, Bannayan-Riley-Ruvalcaba syndrome, Proteus syndrome, and Proteus-like syndrome. Germline PTEN mutations have been identified in a significant proportion of patients with PHTS; however, there are still many individuals with classic diagnostic features for whom mutations have yet to be identified. To address this, we took a haplotype-based approach and investigated the association of specific genomic regions of the PTEN locus with PHTS. We found this locus to be characterized by three distinct haplotype blocks 33 kb, 65 kb, and 43 kb in length. Comparisons of the haplotype distributions for all three blocks differed significantly among patients with PHTS and controls (P=.0098, P<.0001, and P<.0001 for blocks 1, 2, and 3, respectively). "Rare" haplotype blocks and extended haplotypes account for two-to-threefold more PHTS chromosomes than control chromosomes. PTEN mutation-negative patients are strongly associated with a haplotype block spanning a region upstream of PTEN and the gene's first intron (P=.0027). Furthermore, allelic combinations contribute to the phenotypic complexity of this syndrome. Taken together, these data suggest that specific haplotypes and rare alleles underlie the disease etiology in these sample populations; constitute low-penetrance, modifying loci; and, specifically in the case of patients with PHTS for whom traditional mutations have yet to be identified, may harbor pathogenic variant(s) that have escaped detection by standard PTEN mutation-scanning methodologies.     

Ubiquitination regulates PTEN nuclear import and tumor suppression

The PTEN tumor suppressor is frequently affected in cancer cells, and inherited PTEN mutation causes cancer-susceptibility conditions such as Cowden syndrome. PTEN acts as a plasma-membrane lipid-phosphatase antagonizing the phosphoinositide 3-kinase/AKT cell survival pathway. However, PTEN is also found in cell nuclei, but mechanism, function, and relevance of nuclear localization remain unclear. We show that nuclear PTEN is essential for tumor suppression and that PTEN nuclear import is mediated by its monoubiquitination. A lysine mutant of PTEN, K289E associated with Cowden syndrome, retains catalytic activity but fails to accumulate in nuclei of patient tissue due to an import defect. We identify this and another lysine residue as major monoubiquitination sites essential for PTEN import. While nuclear PTEN is stable, polyubiquitination leads to its degradation in the cytoplasm. Thus, we identify cancer-associated mutations of PTEN that target its posttranslational modification and demonstrate how a discrete molecular mechanism dictates tumor progression by differentiating between degradation and protection of PTEN.     

The gene dosage of class Ia PI3K dictates the development of PTEN hamartoma tumor syndrome

The PTEN hamartoma tumor syndrome (PHTS) is a complex disorder caused by germline inactivating mutations of the tumor suppressor gene PTEN. Loss of PTEN function leads to unimpeded phosphatidylinositol-3′-kinase (PI3K) activity and PI3K-driven cell division. Individuals with PHTS develop benign hamartomas in various tissues and have an increased risk of developing malignant diseases. Notably, no effective therapy currently exists for this disorder. Using both genetic mouse models and pharmacological approaches, we recently demonstrated that PI3K p110α and p110β isoforms play spatially distinct but concerted roles in the skin that are required for the development and maintenance of PHTS. We also show that treatment with a pan-PI3K inhibitor prevents the development of skin PHTS and reverses advanced-stage skin hamartomas in vivo. Here, we report that genetic ablation of only 3 out of 4 p110 alleles is sufficient to block the development of skin hamartomas resulting from the complete loss of Pten in mice. Similar to our findings in skin, we now also show that mammary gland neoplastic lesions can be prevented or reversed upon PI3K inhibition in our PHTS mouse model. Our data suggest a possible route to chemoprevention using reduced doses of PI3K inhibitors for PTEN-deficient carrier patients.     

Novel deletion mutation of TRPS1 gene in a Chinese patient of trichorhinophalangeal syndrome type I

Tricho–rhino–phalangeal syndrome (TRPS) is a rare autosomal dominant disorder. Deletion or mutation of the TRPS1 gene leads to the tricho–rhino–phalangeal syndromes type I or type III. In this article, we describe a Chinese patient affected with type I TRPS and showing prominent pilar, rhinal and phalangeal abnormalities. Mutational screening and sequence analysis of TRPS1 gene revealed a previously unidentified four-base-pair deletion of nucleotides 1783–1786 (c.1783_1786delACTT). The mutation causes a frame shift after codon 593, introducing a premature stop codon after 637 residues in the gene sequence. This deletion is an unquestionable loss-of-function mutation, deleting all the functionally important parts of the protein. Our novel discovery indicates that sparse hair and metacarpal defects of tricho–rhino–phalangeal syndromes in this patient are due to this TRPS1 mutation. And this data further supports the critical role of TRPS1 gene in hair and partial skeleton morphogenesis.     

A clinical scoring system for selection of patients for PTEN mutation testing is proposed on the basis of a prospective study of 3042 probands

Cowden syndrome (CS) and Bannayan-Riley-Ruvalcaba syndrome are allelic, defined by germline PTEN mutations, and collectively referred to as PTEN hamartoma tumor syndrome. To date, there are no existing criteria based on large prospective patient cohorts to select patients for PTEN mutation testing. To address these issues, we conducted a multicenter prospective study in which 3042 probands satisfying relaxed CS clinical criteria were accrued. PTEN mutation scanning, including promoter and large deletion analysis, was performed for all subjects. Pathogenic mutations were identified in 290 individuals (9.5%). To evaluate clinical phenotype and PTEN genotype against protein expression, we performed immunoblotting (PTEN, P-AKT1, P-MAPK1/2) for a patient subset (n = 423). In order to obtain an individualized estimation of pretest probability of germline PTEN mutation, we developed an optimized clinical practice model to identify adult and pediatric patients. For adults, a semiquantitative score-the Cleveland Clinic (CC) score-resulted in a well-calibrated estimation of pretest probability of PTEN status. Overall, decreased PTEN protein expression correlated with PTEN mutation status; decreasing PTEN protein expression correlated with increasing CC score (p < 0.001), but not with the National Comprehensive Cancer Network (NCCN) criteria (p = 0.11). For pediatric patients, we identified highly sensitive criteria to guide PTEN mutation testing, with phenotypic features distinct from the adult setting. Our model improved sensitivity and positive predictive value for germline PTEN mutation relative to the NCCN 2010 criteria in both cohorts. We present the first evidence-based clinical practice model to select patients for genetics referral and PTEN mutation testing, further supported biologically by protein correlation.     

Focus: A Multifaceted Battle Against Cancer: The Benefit and Burden of Cancer Screening in Li-Fraumeni Syndrome: A Case Report

Li-Fraumeni syndrome is a rare cancer predisposition syndrome classically associated with remarkably early onset of cancer in families with a typical spectrum of malignancies, including sarcoma, breast cancer, brain tumors, and adrenocortical carcinoma. Because the risks of cancer development are strikingly high for Li-Fraumeni syndrome, aggressive cancer surveillance is often pursued in these individuals. However, optimal screening methods and intervals for Li-Fraumeni syndrome have yet to be determined. In addition, there may be a significant psychosocial burden to intensive cancer surveillance and some prevention modalities. Here, we describe a case of a young woman with a de novo mutation in TP53 and multiple malignancies, with her most recent cancers found at early, curable stages due to aggressive cancer screening. The potential benefits and risks of intensive cancer surveillance in hereditary cancer syndromes is discussed.     

Familiärer Darmkrebs

Up to 5% of colorectal cancer cases are caused by a monogenic inherited disposition. Among these, hereditary nonpolyposis colorectal cancer (Lynch syndrome, HNPCC) accounts for 2–3% and adenomatous polyposis syndromes (familial adenomatous polyposis, FAP and MUTYH-associated polyposis, MAP) for about 1% of cases. Hamartomatous polyposis syndromes (juvenile polyposis syndrome, Peutz-Jeghers syndrome and Cowden syndrome) are rare disorders that are also associated with an increased colorectal cancer risk. The genetic basis is largely known for the tumour syndromes mentioned above. The identification of the causative germline mutation in the respective DNA repair genes (e.g. in HNPCC and MAP) or tumour suppressor genes (FAP or hamartomatous polyposis syndromes) allows confirmation of the diagnosis in affected individuals and provides predictive diagnostics for their healthy relatives. To achieve a targeted and useful molecular diagnostics, it is important that the clinician provides a detailed characterisation of the clinical picture; moreover, family history may also give a hint of the underlying gene defect. The screening of tumour tissue for the presence of a mismatch repair defect should precede mutation analysis in suspected cases of HNPCC, as it is difficult to differentiate between this condition and sporadic colorectal cancer. In contrast, mutation analysis can be directly performed in polyposis syndromes provided the syndrome has been correctly classified by the histology of polyps.     

Protean PTEN: form and function

Germline mutations distributed across the PTEN tumor-suppressor gene have been found to result in a wide spectrum of phenotypic features. Originally shown to be a major susceptibility gene for both Cowden syndrome (CS), which is characterized by multiple hamartomas and an increased risk of breast, thyroid, and endometrial cancers, and Bannayan-Riley-Ruvalcaba syndrome, which is characterized by lipomatosis, macrocephaly, and speckled penis, the PTEN hamartoma tumor syndrome spectrum has broadened to include Proteus syndrome and Proteus-like syndromes. Exon 5, which encodes the core motif, is a hotspot for mutations likely due to the biology of the protein. PTEN is a major lipid 3-phosphatase, which signals down the PI3 kinase/AKT pro-apoptotic pathway. Furthermore, PTEN is a protein phosphatase, with the ability to dephosphorylate both serine and threonine residues. The protein-phosphatase activity has also been shown to regulate various cell-survival pathways, such as the mitogen-activated kinase (MAPK) pathway. Although it is well established that PTEN's lipid-phosphatase activity, via the PI3K/AKT pathway, mediates growth suppression, there is accumulating evidence that the protein-phosphatase/MAPK pathway is equally important in the mediation of growth arrest and other crucial cellular functions.     

Germline inactivation of PTEN and dysregulation of the phosphoinositol-3-kinase/Akt pathway cause human Lhermitte-Duclos disease in adults

Lhermitte-Duclos disease (LDD), or dysplastic gangliocytoma of the cerebellum, is an unusual hamartomatous overgrowth disorder. LDD can be familial or, more commonly, sporadic. It has been only recently recognized that LDD may be associated with Cowden syndrome (CS). Over 80% of patients with CS carry germline mutations in PTEN. It remains unclear whether all cases of LDD, even without features of CS, are caused by germline PTEN mutation and whether somatic PTEN mutation occurs in sporadic LDD. We obtained paraffin-embedded LDD lesions from 18 unselected, unrelated patients and performed mutational analysis of PTEN. Overall, 15 (83%) of 18 samples were found to carry a PTEN mutation. All individuals with mutations were adult-onset patients, but the three without mutations were diagnosed at the ages of 1, 3, and 11 years. Germline DNA was available from six adult-onset cases, and all had germline PTEN mutations. Of these six, two had CS features, one did not have CS features, and three were of unknown CS status. Immunohistochemistry revealed that 75% of the LDD samples had complete or partial loss of PTEN expression accompanied by elevated phosphorylated Akt, specifically in the dysplastic gangliocytoma cells. These data suggest that the loss of PTEN function is sufficient to cause LDD. The high frequency and spectrum of germline PTEN mutations in patients ascertaining by LDD alone confirm that LDD is an important defining feature of CS. Individuals with LDD, even without apparent CS features, should be counseled as in CS.     

Familial Hyperparathyroidism Due to A Germline Mutation of the Cdc73 Gene: Implications for Management and Age-Appropriate Testing of Relatives At Risk

ObjectiveTo discuss the implications of a young age at diagnosis in a family member with hyperparathyroidismjaw tumor syndrome, the youngest published case to date, due to a mutation of the CDC73 gene (formerly known as HRPT2); to review this family with regard to modifications of guidelines for surveillance of hyperparathyroidism and other associated features in affected and at-risk relatives; and to discuss surgical recommendations in this syndrome.MethodsA review of English-language publications in PubMed and a review of GeneReviews were conducted pertaining to the subject of familial hyperparathyroidism. A case is described, and the family pedigree is discussed.ResultsReview of the literature revealed that CDC73-related disorder has not previously been reported in patients younger than 10 years. This finding has been the basis for the recommendation for initiation of surveillance for disease manifestations at that age. Review of the family history of our current patient revealed a 7-yearold nephew with hypercalcemia attributable to primary hyperparathyroidism.ConclusionSurveillance of hyperparathyroidism in affected persons and genetic testing of relatives at risk are currently recommended to start at 10 years of age. We recommend that these be conducted at a younger age, preferably 5 to 10 years before the earliest diagnosis of hyperparathyroidism within the family, and potentially at birth in families with a known mutation of the CDC73 gene, in light of the malignant potential of the disease. (Endocr Pract. 2011;17:602-609)     

Mowat–Wilson syndrome detected by using high resolution microarray

Individuals with Mowat–Wilson syndrome (MWS; OMIM#235730) have characteristic facial features, a variety of congenital anomalies such as Hirschsprung disease, and intellectual disabilities caused by mutation or deletion of ZEB2 gene. This deletion or cytogenetic abnormality has been reported primarily from Europe, Australia and the United States, but not in Korea. Here we report a patient with characteristic facial features of MWS, developmental delay and spasticity. High resolution microarray analysis revealed 0.9 Mb deletion of 2q22.3 involving two genes: ZEB2 and GTDC1. This case shows the important role of high resolution microarray in patients with unexplained psychomotor retardation and/or facial dysmorphism. Knowledge about the most striking clinical signs and implementation of effective molecular tests like microarray could significantly increase the detection rate of new cases of MWS in Korea. This is the first reported case of MWS in Korea.     

X-linked creatine-transporter gene (SLC6A8) defect: a new creatine-deficiency syndrome

We report the first X-linked creatine-deficiency syndrome caused by a defective creatine transporter. The male index patient presented with developmental delay and hypotonia. Proton magnetic-resonance spectroscopy of his brain revealed absence of the creatine signal. However, creatine in urine and plasma was increased, and guanidinoacetate levels were normal. In three female relatives of the index patient, mild biochemical abnormalities and learning disabilities were present, to various extents. Fibroblasts from the index patient contained a hemizygous nonsense mutation in the gene SLC6A8 and were defective in creatine uptake. The three female relatives were heterozygous for this mutation in SLC6A8, which has been mapped to Xq28.     

PTEN catalysis of phospholipid dephosphorylation reaction follows a two-step mechanism in which the conserved aspartate-92 does not function as the general acid--mechanistic analysis of a familial Cowden disease-associated PTEN mutation

PTEN exerts its tumour suppressor function by dephosphorylating the phospholipid second messenger phosphatidylinositol-3,4,5-trisphosphate (PIP(3)). Herein, we demonstrate that the PTEN-catalysed PIP(3) dephosphorylation reaction involves two-steps: (i) formation of a phosphoenzyme intermediate (PE) in which Cys-124 in the active site is thiophosphorylated, and (ii) hydrolysis of PE. For protein tyrosine- and dual-specificity phosphatases, catalysis requires the participation of a conserved active site aspartate as the general acid in Step 1. Its mutation to alanine severely limits PE formation. However, mutation of the homologous Asp-92 in PTEN does not significantly limit PE formation, indicating that Asp-92 does not act as the general acid. G129E is a common germline PTEN mutations found in Cowden syndrome patients. Mechanistic analysis reveals that this mutation inactivates PTEN by both significantly slowing down Step 1 and abolishing the ability to catalyse Step 2. Taken together, our results highlight the mechanistic similarities and differences between PTEN and the conventional protein phosphatases and reveal how a disease-associated mutation inactivates PTEN.     

Germline BAP1 Mutations Predispose to Renal Cell Carcinomas

The genetic cause of some familial nonsyndromic renal cell carcinomas (RCC) defined by at least two affected first-degree relatives is unknown. By combining whole-exome sequencing and tumor profiling in a family prone to cases of RCC, we identified a germline BAP1 mutation c.277A>G (p.Thr93Ala) as the probable genetic basis of RCC predisposition. This mutation segregated with all four RCC-affected relatives. Furthermore, BAP1 was found to be inactivated in RCC-affected individuals from this family. No BAP1 mutations were identified in 32 familial cases presenting with only RCC. We then screened for germline BAP1 deleterious mutations in familial aggregations of cancers within the spectrum of the recently described BAP1-associated tumor predisposition syndrome, including uveal melanoma, malignant pleural mesothelioma, and cutaneous melanoma. Among the 11 families that included individuals identified as carrying germline deleterious BAP1 mutations, 6 families presented with 9 RCC-affected individuals, demonstrating a significantly increased risk for RCC. This strongly argues that RCC belongs to the BAP1 syndrome and that BAP1 is a RCC-predisposition gene.     

Dynamics and structural stability effects of germline PTEN mutations associated with cancer versus autism phenotypes

Individuals with germline mutations in the tumor suppressor gene phosphatase and tensin homolog (PTEN), irrespective of clinical presentation, are diagnosed with PTEN hamartoma tumor syndrome (PHTS). PHTS confers a high risk of breast, thyroid, and other cancers or autism spectrum disorder (ASD) with macrocephaly. It remains unclear why mutations in one gene can lead to seemingly disparate phenotypes. Thus, we sought to identify differences in ASD vs. cancer-associated germline PTEN missense mutations by investigating putative structural effects induced by each mutation. We utilized a theoretical computational approach combining in silico structural analysis and molecular dynamics (MD) to interrogate 17 selected mutations from our patient population: six mutations were observed in patients with ASD (only), six mutations in patients with PHTS-associated cancer (only), four mutations shared across both phenotypes, and one mutation with both ASD and cancer. We demonstrate structural stability changes where all six cancer-associated mutations showed a global decrease in structural stability and increased dynamics across the domain interface with a proclivity to unfold, mediating a closed (inactive) active site. In contrast, five of the six ASD-associated mutations showed localized destabilization that contribute to the partial opening of the active site. Our results lend insight into distinctive structural effects of germline PTEN mutations associated with PTEN-ASD vs. those associated with PTEN-cancer, potentially aiding in identification of the shared and separate molecular features that contribute to autism or cancer, thus, providing a deeper understanding of genotype–phenotype relationships for germline PTEN mutations.     

15q11.2 microdeletion and FMR1 premutation in a family with intellectual disabilities and autism

Genomic rearrangements of chromosome 15q11–q13 are responsible for diverse phenotypes including intellectual disabilities and autism. 15q11.2 deletion, implicating common PWS/AS breakpoints BP1–BP2, has been described in patients with delayed motor and speech development and behavioural problems. Here we report the clinical and molecular characterisation of a maternally inherited BP1–BP2 deletion in two siblings with intellectual, motor and speech delay, autistic syndrome disorder and several dysmorphic features. One of the patients was also a carrier of an FMR1 allele in the low premutation range. The four genes within the deletion were under-expressed in all deletion carriers but FMR1 mRNA levels remained normal. Our results suggest that BP1-BP2 deletion could be considered as a risk factor for neuropsychological phenotypes and that it presents with variable clinical expressivity.     

Managing the risk of cancer in Cowden syndrome: a case report

ABSTRACT: INTRODUCTION: Cowden syndrome is a rare cancer predisposition syndrome inherited in an autosomaldominantfashion. The syndrome is characterized by hamartomatous polyps that affectmultiple organs: skin, mucous membranes, thyroid, breast, gastrointestinal tract,endometrium and brain. It is also associated with an increased risk of developing malignancyin many tissues but especially breast, thyroid and endometrium. CASE PRESENTATION: We present the case of a 30-year-old Tunisian woman with mental retardation who presentedto our facility with rectal hamartomatous polyps. Her medical history included fibrocysticdisease of the breast over the last three years. A physical examination revealed macrocephaly,hyperkeratotic papules on the mid-facial skin, palmoplantar keratosis and oral mucosalpapillomatosis. A breast examination revealed nodular breast tissue bilaterally and a diffusethyroid goiter. Our patient was clinically euthyroid. A total thyroidectomy was performed. Ahistopathologic examination revealed thyroid papillary carcinoma. A gastrointestinalevaluation revealed esophageal and gastric polyps. Biopsies showed hyperplastic andadenomatous lesions associated with Helicobacter pylori. A final diagnosis of Cowdensyndrome was made according to the syndrome testing criteria adapted by the US NationalComprehensive Cancer Network. A prophylactic bilateral mastectomy was proposed butrefused by our patient. Our patient was kept under surveillance for breast and colorectalmalignancies. CONCLUSIONS: Early and accurate diagnosis of Cowden syndrome is essential because it is a cancerpredisposition syndrome that carries an increased risk for developing malignancy in manytissues, especially breast and thyroid. For this reason, education regarding the signs andsymptoms of cancer is important. All patients must be screened for malignancies and optionsfor prophylactic mastectomy should be discussed. Guidelines for cancer screening includingsurveillance and management plans for these patients should be distinguished from those ofthe general population, and may lead to a more timely diagnosis and treatment of cancersassociated with this syndrome.