WRN Mutation Update: Mutation Spectrum, Patient Registries, and Translational Prospects

Precision Radiotherapy and Radiation Risk Assessment: How Do We Overcome Radiogenomic Diversity?

Precision medicine is a rapidly developing area that aims to deliver targeted therapies based on individual patient characteristics. However, current radiation treatment is not yet personalized; consequently, there is a critical need for specific patient characteristics of both tumor and normal tissues to be fully incorporated into dose prescription. Furthermore, current risk assessment following environmental, occupational, or accidental exposures to radiation is based on population effects, and does not account for individual diversity underpinning radiosensitivity. The lack of personalized approaches in both radiotherapy and radiation risk assessment resulted in the current situation where a population-based model, effective dose, is being used. In this review article, to stimulate scientific discussion for precision medicine in both radiotherapy and radiation risk assessment, we propose a novel radiological concept and metric - the personalized dose and the personalized risk index - that incorporate individual physiological, lifestyle-related and genomic variations and radiosensitivity, outlining the potential clinical application for precision medicine. We also review on recent progress in both genomics and biobanking research, which is promising for providing novel insights into individual radiosensitivity, and for creating a novel conceptual framework of precision radiotherapy and radiation risk assessment.

Characteristic Clinical Features of Werner Syndrome with a Novel Compound Heterozygous WRN Mutation c.1720+1G>A Plus c.3139-1G>C

Werner syndrome (WS) is an autosomal recessive progeroid disorder caused by mutations in the WRN gene (WRN). Most Japanese WS patients are born from a consanguineous marriage with homozygous WRN mutations. We herein report a rare WS patient born from non-consanguineous parents with compound heterozygous WRN mutations with a novel heterogeneous c.1720+1G>A substitution plus the most frequent heterogeneous c.3139-1G>C substitution among Japanese. Although the present case showed clinical characteristics common to previous Japanese WS patients, he had not developed any malignant tumors as of 43 years of age, suggesting that WS patients with this particular genetic mutation have a different phenotype than others.

Werner syndrome helicase is a selective vulnerability of microsatellite instability-high tumor cells

Targeted cancer therapy is based on exploiting selective dependencies of tumor cells. By leveraging recent functional screening data of cancer cell lines we identify Werner syndrome helicase (WRN) as a novel specific vulnerability of microsatellite instability-high (MSI-H) cancer cells. MSI, caused by defective mismatch repair (MMR), occurs frequently in colorectal, endometrial and gastric cancers. We demonstrate that WRN inactivation selectively impairs the viability of MSI-H but not microsatellite stable (MSS) colorectal and endometrial cancer cell lines. In MSI-H cells, WRN loss results in severe genome integrity defects. ATP-binding deficient variants of WRN fail to rescue the viability phenotype of WRN-depleted MSI-H cancer cells. Reconstitution and depletion studies indicate that WRN dependence is not attributable to acute loss of MMR gene function but might arise during sustained MMR-deficiency. Our study suggests that pharmacological inhibition of WRN helicase function represents an opportunity to develop a novel targeted therapy for MSI-H cancers.

Plugged into the Ku-DNA hub: The NHEJ network

In vertebrates, double-strand breaks in DNA are primarily repaired by Non-Homologous End-Joining (NHEJ). The ring-shaped Ku heterodimer rapidly senses and threads onto broken DNA ends forming a recruiting hub. Through protein-protein contacts eventually reinforced by protein-DNA interactions, the Ku-DNA hub attracts a series of specialized proteins with scaffolding and/or enzymatic properties. To shed light on these dynamic interplays, we review here current knowledge on proteins directly interacting with Ku and on the contact points involved, with a particular accent on the different classes of Ku-binding motifs identified in several Ku partners. An integrated structural model of the core NHEJ network at the synapsis step is proposed.

Werner's Syndrome: Understanding the Phenotype of Premature Aging-First Case Described in Colombia

Werner's syndrome (WS) is an autosomal recessive genetic disease, which is mainly characterized by scleroderma-like skin changes, juvenile cataracts, short stature, and signs of premature aging. We report a case of a 48-year-old male patient, who presents with cardinal signs of WS including high-pitched voice, sclerotic skin lesions mainly on feet, premature greying of scalp hair, bilateral cataracts, and "bird-like" facial appearance. In addition, the patient presents other clinical characteristics observed in patients with WS such as short stature, type 2 diabetes mellitus, hypogonadism, parental consanguinity, and a history of a sibling with similar clinical characteristics. WRN gene sequencing identified the homozygous pathogenic variant NM_00553.4: c.2581C>T (NP_000544.2: pGln861Ter). This is the first case of WS reported in the Colombian population. We report this case to avoid misdiagnosis of this infrequent condition and allow timely identification of potential complications associated with premature aging, especially malignancies, cardiovascular and metabolic diseases.

Successful Cord Blood Transplantation in a Werner Syndrome Patient with High-risk Myelodysplastic Syndrome

Werner syndrome (WS) confers a high risk of the development of neoplasias, including hematological malignancies, and curative treatment for these malignancies is difficult to achieve. A 44-year-old man with myelodysplastic syndrome was admitted to our hospital. He was diagnosed with mutation-proven WS. He underwent cord blood transplantation (CBT) following fludarabine, busulfan, and melphalan administration. A chimerism analysis of his marrow blood on day 62 showed a donor pattern >95%, which confirmed engraftment. The patient lived for 15 months while maintaining remission of MDS without treatment-related toxicity. Our case shows that CBT can be a treatment modality for WS patients with hematological malignancies.

CTC1 mutations in a Brazilian family with progeroid features and recurrent bone fractures

BACKGROUND

Cerebroretinal microangiopathy with calcifications and cysts (CRMCC) is an autosomal recessive disorder caused by pathogenic variants of the conserved telomere maintenance component 1 (CTC1) gene. The CTC1 forms the telomeric capping complex, CST, which functions in telomere homeostasis and replication.

METHODS

A Brazilian pedigree and an Australian pedigree were referred to the International Registry of Werner Syndrome (Seattle, WA, USA), with clinical features of accelerated aging and recurrent bone fractures. Whole exome sequencing was performed to identify the genetic causes.

RESULTS

Whole exome sequencing of the Brazilian pedigree revealed compound heterozygous pathogenic variants in CTC1: a missense mutation (c.2959C>T, p.Arg987Trp) and a novel stop codon change (c.322C>T, p.Arg108*). The Australian patient carried two novel heterozygous CTC1 variants, c.2916G>T, p.Val972Gly and c.2926G>T, p.Val976Phe within the same allele. Both heterozygous variants were inherited from the unaffected father, excluding the diagnosis of CRMCC in this pedigree. Cell biological studies demonstrated accumulation of double strand break foci in lymphoblastoid cell lines derived from the patients. Increased DSB foci were extended to non-telomeric regions of the genome, in agreement with previous biochemical studies showing a preferential binding of CTC1 protein to GC-rich sequences.

CONCLUSION

CTC1 pathogenic variants can present with unusual manifestations of progeria accompanied with recurrent bone fractures. Further studies are needed to elucidate the disease mechanism leading to the clinical presentation with intra-familial variations of CRMCC.

Werner Syndrome Protein and DNA Replication

Werner Syndrome (WS) is an autosomal recessive disorder characterized by the premature development of aging features. Individuals with WS also have a greater predisposition to rare cancers that are mesenchymal in origin. Werner Syndrome Protein (WRN), the protein mutated in WS, is unique among RecQ family proteins in that it possesses exonuclease and 3' to 5' helicase activities. WRN forms dynamic sub-complexes with different factors involved in DNA replication, recombination and repair. WRN binding partners either facilitate its DNA metabolic activities or utilize it to execute their specific functions. Furthermore, WRN is phosphorylated by multiple kinases, including Ataxia telangiectasia mutated, Ataxia telangiectasia and Rad3 related, c-Abl, Cyclin-dependent kinase 1 and DNA-dependent protein kinase catalytic subunit, in response to genotoxic stress. These post-translational modifications are critical for WRN to function properly in DNA repair, replication and recombination. Accumulating evidence suggests that WRN plays a crucial role in one or more genome stability maintenance pathways, through which it suppresses cancer and premature aging. Among its many functions, WRN helps in replication fork progression, facilitates the repair of stalled replication forks and DNA double-strand breaks associated with replication forks, and blocks nuclease-mediated excessive processing of replication forks. In this review, we specifically focus on human WRN's contribution to replication fork processing for maintaining genome stability and suppressing premature aging. Understanding WRN's molecular role in timely and faithful DNA replication will further advance our understanding of the pathophysiology of WS.

Nonfunctional mutant Wrn protein leads to neurological deficits, neuronal stress, microglial alteration, and immune imbalance in a mouse model of Werner syndrome

Werner syndrome (WS) is a premature aging disorder caused by mutations in a RecQ-family DNA helicase, WRN. Mice lacking part of the helicase domain of the WRN orthologue exhibit many phenotypic features of WS, including metabolic abnormalities and a shorter lifespan. Yet, little is known about the impact of WRN mutations on the central nervous system in both humans and mouse models of WS. In the current study, we have performed a longitudinal behavioral assessment on mice bearing a Wrn helicase deletion. Behavioral tests demonstrated a loss of motor activity and coordination, reduction in perception, increase in repetitive behavior, and deficits in both spatial and social novelty memories in Wrn mutant mice compared to age-matched wild type mice. These neurological deficits were associated with biochemical and histological changes in the brain of aged Wrn mutant mice. Microglia, resident immune cells that regulate neuronal plasticity and function in the brain, were hyper-ramified in multiple regions involved with the behavioral deficits of Wrn mutant mice. Furthermore, western analyses indicated that Wrn mutant mice exhibited an increase of oxidative stress markers in the prefrontal cortex. Supporting these findings, electron microscopy studies revealed increased cellular aging and oxidative stress features, among microglia and neurons respectively, in the prefrontal cortex of aged Wrn mutant mice. In addition, multiplex immunoassay of serum identified significant changes in the expression levels of several pro- and anti-inflammatory cytokines. Taken together, these findings indicate that microglial dysfunction and neuronal oxidative stress, associated with peripheral immune system alterations, might be important driving forces leading to abnormal neurological symptoms in WS thus suggesting potential therapeutic targets for interventions.

Cutaneous Manifestations of Scleroderma and Scleroderma-Like Disorders: a Comprehensive Review

Scleroderma refers to an autoimmune connective tissue fibrosing disease, including three different subsets: localized scleroderma, limited cutaneous systemic sclerosis, and diffuse cutaneous systemic sclerosis with divergent patterns of organ involvement, autoantibody profiles, management, and prognostic implications. Although systemic sclerosis is considered the disease prototype that causes cutaneous sclerosis, there are many other conditions that can mimic and be confused with SSc. They can be classified into immune-mediated/inflammatory, immune-mediated/inflammatory with abnormal deposit (mucinoses), genetic, drug-induced and toxic, metabolic, panniculitis/vascular, and (para)neoplastic disorders according to clinico-pathological and pathogenetic correlations. This article reviews the clinical presentation with emphasis on cutaneous disease, etiopathogenesis, diagnosis, and treatment options available for the different forms of scleroderma firstly and for scleroderma-like disorders, including scleromyxedema, scleredema, nephrogenic systemic fibrosis, eosinophilic fasciitis, chronic graft-versus-host disease, porphyria cutanea tarda, diabetic stiff-hand syndrome (diabetic cheiroartropathy), and other minor forms. This latter group of conditions, termed also scleroderma mimics, sclerodermiform diseases, or pseudosclerodermas, shares the common thread of skin thickening but presents with distinct cutaneous manifestations, skin histology, and systemic implications or disease associations, differentiating each entity from the others and from scleroderma. The lack of Raynaud's phenomenon, capillaroscopic abnormalities, or scleroderma-specific autoantibodies is also important diagnostic clues. As cutaneous involvement is the earliest, most frequent and characteristic manifestation of scleroderma and sclerodermoid disorders, dermatologists are often the first-line doctors who must be able to promptly recognize skin symptoms to provide the affected patient a correct diagnosis and appropriate management.

Biallelic WRN Mutations in Newly Identified Japanese Werner Syndrome Patients

Werner syndrome (WS) is a rare autosomal recessive disorder characterized by systemic accelerated aging. It is caused by pathogenic variants of the WRN gene that encodes a nuclear helicase. In this report, we describe 4 newly identified WS cases among those referred to the Japanese Werner Consortium, Chiba University, Japan. All 4 cases were compound heterozygotes of the Japanese founder mutation, c.3139-1G>C, and a novel null pathogenic variant, c.1587G>A, c.2448+1G>A, or c.3233+1G>T, or an amino acid substitution variant, c.1720G>A, p.Gly574Arg. These 3 null pathogenic variants were not previously described. The p. Gly574Arg was previously reported in a European patient, and the identification of the second p. Gly574Arg case, with classical WS features, further confirmed the pathogenic nature of this variant. For the case with c.3233+1G>T, we determined the phase of 2 disease-causing mutations and demonstrated that they are on different chromosomes. This assay would be particularly important for those cases with ambiguous clinical diagnosis.

RECQ helicase disease and related progeroid syndromes: RECQ2018 meeting

Progeroid syndrome is a group of disorders characterized by the early onset of diseases that are associated with aging. Best known examples are Werner syndrome, which is adult onset and results from disease-causing DNA sequence variants in the RecQ helicase gene WRN, and Hutchison-Gilford progeria syndrome, which is childhood-onset and results from unique, recurrent disease-causing DNA sequence variants of the gene LMNA that encodes nuclear intermediate filaments. Related single gene RecQ disorders are Bloom syndrome and Rothmund-Thomson syndrome. The RecQ disorders Cockayne syndrome and xeroderma pigmentosum result from disease-causing DNA sequence variants in genes involved in the nucleotide excision repair pathway. RECQ2018: The International Meeting on RECQ Helicases and Related Diseases was held on February 16-18, 2018 in Chiba, Japan. The purpose of the meeting was to facilitate clinical and research collaborations for the goal of developing effective treatments for RECQ disorders and other progeroid syndromes.

Werner syndrome: a model for sarcopenia due to accelerated aging

Werner syndrome (WS) is a rare inheritable progeroid syndrome caused by a mutation in the WRN gene. Although WS has been described as a characteristic appearance of very slender extremities with a stocky trunk, few studies have investigated the loss of muscle mass, fat mass distribution (body composition), and mobility according to age and sex. Therefore, the aim of this study was to precisely describe the body composition in WS. Nine Japanese patients with WS (four males and five females; mean age 48±8.8 years) were recruited. Body composition was examined by dual-energy X-ray absorptiometry and computed tomography (CT). The hand grip strength and mobility were evaluated using the two-step test, stand-up test and 25-question geriatric locomotive function scale (GLFS). The mean skeletal muscle index (SMI) was 4.0±0.6 kg/m². SMI of all patients met the criteria of sarcopenia, even though some patients were aged < 40 years. All patients also showed deceased mobility. In conclusion, these results indicate that all patients with WS, even those aged < 40 years, had already lost muscle mass to the level of sarcopenia. Continued research on sarcopenia in WS might facilitate the discovery of novel mechanisms and development of new treatment strategies for sarcopenia.

Werner syndrome (WRN) gene variants and their association with altered function and age-associated diseases

Werner syndrome (WS) is a heritable autosomal recessive human disorder characterized by the premature onset of several age-associated pathologies including cancer. The protein defective in WS patients, WRN, is encoded by a member of the human RECQ gene family that contains both a DNA exonuclease and a helicase domain. WRN has been shown to participate in several DNA metabolic pathways including DNA replication, recombination and repair, as well as telomere maintenance and transcription modulation. Here we review base pair-level genetic variation that has been documented in WRN, with an emphasis on non-synonymous coding single nucleotide polymorphisms (SNPs) and their associations with anthropomorphic features, longevity and disease risk. These associations have been challenging to identify, as many reported WRN SNP associations appear to be further conditioned upon ethnic, age, gender or other environmental co-variables. The WRN variant phenotypic associations identified to date are intriguing, and several are of clear clinical import. Consequently, it will be important to extend these initial associations and to identify the mechanisms and conditions under which specific WRN variants may compromise WRN function to drive cellular and organismal phenotypes as well as disease risk.

Recent Advances in Understanding Werner Syndrome

Aging, the universal phenomenon, affects human health and is the primary risk factor for major disease pathologies. Progeroid diseases, which mimic aging at an accelerated rate, have provided cues in understanding the hallmarks of aging. Mutations in DNA repair genes as well as in telomerase subunits are known to cause progeroid syndromes. Werner syndrome (WS), which is characterized by accelerated aging, is an autosomal-recessive genetic disorder. Hallmarks that define the aging process include genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulation of nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, and altered intercellular communication. WS recapitulates these hallmarks of aging and shows increased incidence and early onset of specific cancers. Genome integrity and stability ensure the normal functioning of the cell and are mainly guarded by the DNA repair machinery and telomeres. WRN, being a RecQ helicase, protects genome stability by regulating DNA repair pathways and telomeres. Recent advances in WS research have elucidated WRN’s role in DNA repair pathway choice regulation, telomere maintenance, resolution of complex DNA structures, epigenetic regulation, and stem cell maintenance.

Tumor Syndromes That Include Bone Tumors: An Update

Tumor syndromes, including bone neoplasias, are genetic predisposing conditions characterized by the development of a pattern of malignancies within a family at an early age of onset. Occurrence of bilateral, multifocal, or metachronous neoplasias and specific histopathologic findings suggest a genetic predisposition syndrome. Additional clinical features not related to the neoplasia can be a hallmark of specific genetic syndromes. Mostly, those diseases have an autosomal dominant pattern of inheritance with variable percentage of penetrance. Some syndromic disorders with an increased tumor risk may show an autosomal recessive transmission or are related to somatic mosaicism. Many genetic tumor syndromes are known. This update is specifically focused on syndromes predisposing to osteosarcoma and chondrosarcoma.

Osteosarcoma: Molecular Pathogenesis and iPSC Modeling

Rare hereditary disorders provide unequivocal evidence of the importance of genes in human disease pathogenesis. Familial syndromes that predispose to osteosarcomagenesis are invaluable in understanding the underlying genetics of this malignancy. Recently, patient-derived induced pluripotent stem cells (iPSCs) have been successfully utilized to model Li-Fraumeni syndrome (LFS)-associated bone malignancy, demonstrating that iPSCs can serve as an in vitro disease model to elucidate osteosarcoma etiology. We provide here an overview of osteosarcoma predisposition syndromes and review recently established iPSC disease models for these familial syndromes. Merging molecular information gathered from these models with the current knowledge of osteosarcoma biology will help us to gain a deeper understanding of the pathological mechanisms underlying osteosarcomagenesis and will potentially aid in the development of future patient therapies.

Uncommon cause of cirrhosis-A case of Werner syndrome with a novel WRN mutation

Werner syndrome is a rare progeroid syndrome caused by the WRN gene mutation. It is characterized by a general appearance of premature aging, diabetes mellitus, and atherosclerosis, and an increased risk of malignancies. We report a patient who presented with hematemesis due to cirrhosis of liver and was subsequently diagnosed with Werner syndrome. Further genetic analysis showed a novel mutation in the WRN gene which has not previously been reported. Werner syndrome should be considered for the cases of liver cirrhosis when accompanied by the features of accelerated aging.

Human RECQ Helicase Pathogenic Variants, Population Variation and "Missing" Diseases

Heritable loss of function mutations in the human RECQ helicase genes BLM, WRN, and RECQL4 cause Bloom, Werner, and Rothmund-Thomson syndromes, cancer predispositions with additional developmental or progeroid features. In order to better understand RECQ pathogenic and population variation, we systematically analyzed genetic variation in all five human RECQ helicase genes. A total of 3,741 unique base pair-level variants were identified, across 17,605 potential mutation sites. Direct counting of BLM, RECQL4, and WRN pathogenic variants was used to determine aggregate and disease-specific carrier frequencies. The use of biochemical and model organism data, together with computational prediction, identified over 300 potentially pathogenic population variants in RECQL and RECQL5, the two RECQ helicases that are not yet linked to a heritable deficiency syndrome. Despite the presence of these predicted pathogenic variants in the human population, we identified no individuals homozygous for any biochemically verified or predicted pathogenic RECQL or RECQL5 variant. Nor did we find any individual heterozygous for known pathogenic variants in two or more of the disease-associated RECQ helicase genes BLM, RECQL4, or WRN. Several postulated RECQ helicase deficiency syndromes-RECQL or RECQL5 loss of function, or compound haploinsufficiency for the disease-associated RECQ helicases-may remain missing, as they likely incompatible with life.