Caspase 5 depletion is linked to hyper-inflammatory response and progeroid syndrome

A progeroid family was found to harbor a pathogenic variant in the CASP5 gene that encodes inflammatory caspase 5. Caspase 5-depleted fibroblasts exhibited hyper-activation of inflammatory cytokines in response to pro-inflammatory stimuli. Long-term intermittent hyper-inflammatory response is likely the cause of the accelerated aging phenotype comprised of earlier onset of common aging diseases, supporting inflammaging as a potential common disease mechanism of progeroid syndromes and possibly normative aging.

Maternal histone methyltransferases antagonistically regulate monoallelic expression in C. elegans

Undefined epigenetic programs act to probabilistically silence individual autosomal alleles, generating unique individuals, even from genetic clones. This sort of random monoallelic expression can explain variation in traits and diseases that differences in genes and environments cannot. Here, we developed the nematode Caenorhabditis elegans to study monoallelic expression in whole tissues, and defined a developmental genetic regulation pathway. We found maternal H3K9 histone methyltransferase (HMT) SET-25/SUV39/G9a works with HPL-2/HP1 and LIN-61/L3MBTL2 to randomly silence alleles in the intestinal progenitor E-cell of 8-cell embryos to cause monoallelic expression. SET-25 was antagonized by another maternal H3K9 HMT, MET-2/SETDB1, which works with LIN-65/ATF7ZIP and ARLE-14/ARL14EP to prevent monoallelic expression. The HMT-catalytic SET domains of both MET-2 and SET-25 were required for regulating monoallelic expression. Our data support a model wherein SET-25 and MET-2 regulate histones during development to generate patterns of somatic monoallelic expression that are persistent but not heritable.

Woodhouse-Sakati syndrome in an Indian patient with a novel pathogenic variant

Woodhouse-Sakati syndrome consists of hypogonadism, diabetes mellitus, alopecia, ECG abnormalities, and dystonia. This condition is caused by the loss of function of the DCAF17 gene. Most of the patients have been reported from Greater Middle Eastern countries. We report a 38 male from southern India who presented with syncope and massive hemoptysis due to ruptured bronchopulmonary collaterals. He also had alopecia, cataracts, recently diagnosed diabetes and hypogonadism. Whole exome sequencing showed a novel homozygous truncating variant in the DCAF17 gene. Despite embolization of the aortopulmonary collaterals, the patient died of recurrent hemoptysis.

Key elements of cellular senescence involve transcriptional repression of mitotic and DNA repair genes through the p53-p16/RB-E2F-DREAM complex

Cellular senescence is a dynamic stress response process that contributes to aging. From initiation to maintenance, senescent cells continuously undergo complex molecular changes and develop an altered transcriptome. Understanding how the molecular architecture of these cells evolve to sustain their non-proliferative state will open new therapeutic avenues to alleviate or delay the consequences of aging. Seeking to understand these molecular changes, we studied the transcriptomic profiles of endothelial replication-induced senescence and senescence induced by the inflammatory cytokine, TNF-α. We previously reported gene expressional pattern, pathways, and the mechanisms associated with upregulated genes during TNF-α induced senescence. Here, we extend our work and find downregulated gene signatures of both replicative and TNF-α senescence were highly overlapped, involving the decreased expression of several genes associated with cell cycle regulation, DNA replication, recombination, repair, chromatin structure, cellular assembly, and organization. We identified multiple targets of p53/p16-RB-E2F-DREAM that are essential for proliferation, mitotic progression, resolving DNA damage, maintaining chromatin integrity, and DNA synthesis that were repressed in senescent cells. We show that repression of multiple target genes in the p53/p16-RB-E2F-DREAM pathway collectively contributes to the stability of the senescent arrest. Our findings show that the regulatory connection between DREAM and cellular senescence may play a potential role in the aging process.

Renal dysfunction, malignant neoplasms, atherosclerotic cardiovascular diseases, and sarcopenia as key outcomes observed in a three-year follow-up study using the Werner Syndrome Registry

Werner syndrome is an adult-onset progeria syndrome that results in various complications. This study aimed to clarify the profile and secular variation of the disease. Fifty-one patients were enrolled and registered in the Werner Syndrome Registry. Their data were collected annually following registration. A cross-sectional analysis at registration and a longitudinal analysis between the baseline and each subsequent year was performed. Pearson's chi-squared and Wilcoxon signed-rank tests were used. Malignant neoplasms were observed from the fifth decade of life (mean onset: 49.7 years) and were observed in approximately 30% of patients during the 3-year survey period. Regarding renal function, the mean estimated glomerular filtration rate calculated from serum creatinine (eGFRcre) and eGFRcys, which were calculated from cystatin C in the first year, were 98.3 and 83.2 mL/min/1.73 m2, respectively, and differed depending on the index used. In longitudinal analysis, the average eGFRcre for the first and fourth years was 74.8 and 63.4 mL/min/1.73 m2, showing a rapid decline. Secular changes in Werner syndrome in multiple patients were identified. The prevalence of malignant neoplasms is high, and renal function may decline rapidly. It is, therefore, necessary to carry out active and detailed examinations and pay attention to the type and dose of the drugs used.

Rapid emergence of transcriptional heterogeneity upon molecular stress predisposes cells to two distinct states of senescence

Slowing aging can reduce the risk of chronic diseases. In particular, eliminating senescent cells is a promising approach to slow aging. Previous studies found that both cells from older animals and senescent cells have noisy gene expression. Here, we performed a large-scale single-cell RNA-sequencing time course to understand how transcriptional heterogeneity develops among senescent cells. We found that cells experiencing senescence-inducing oxidative stress rapidly adopt one of two major transcriptional states. One senescent cell state is associated with stress response, and the other is associated with tissue remodeling. We did not observe increased stochastic gene expression. This data is consistent with the idea that reproducible, limited, distinct, and coherent transcriptional states exist in senescent cell populations. These physiologically distinct senescent cell subtypes may each affect the aging process in unique ways and constitute a source of heterogeneity in aging.

Accelerated epigenetic aging and DNA methylation alterations in Berardinelli-Seip congenital lipodystrophy

Berardinelli-Seip Congenital Lipodystrophy type 2 (CGL2) is a very rare human genetic disorder with potential significance to the understanding of the pathobiology of aging. CGL2 patients display characteristic progeroid features and suffer from type 2 diabetes, insulin resistance, and fatty liver. In this study, we profiled genome-wide DNA methylation levels in CGL2 patients with BSCL2 mutations to study epigenetic age acceleration and DNA methylation alterations. This analysis revealed significant age acceleration in blood DNA of CGL2 patients using both first and second generation epigenetic clocks. We also observed a shortened lifespan of C. elegans following knockdown of the BSCL2 homolog seip-1 on a daf-16/Foxo mutant background. DNA methylation analysis revealed significant differentially methylated sites enriched for lyase activity, kinase regulator activity, protein kinase regulator activity, and kinase activator activity. We could also observe significant hypomethylation in the promoter of the Dual Specificity Phosphatase 22 (DUSP22) gene when comparing CGL2 patients vs controls. We conclude that in line with the observed progeroid features, CGL2 patients exhibit significant epigenetic age acceleration and DNA methylation alterations that might affect pathways/genes of potential relevance to the disease.

TNF-α/IFN-γ synergy amplifies senescence-associated inflammation and SARS-CoV-2 receptor expression via hyper-activated JAK/STAT1

Older age and underlying conditions such as diabetes/obesity or immunosuppression are leading host risk factors for developing severe complications from COVID‐19 infection. The pathogenesis of COVID‐19‐related cytokine storm, tissue damage, and fibrosis may be interconnected with fundamental aging processes, including dysregulated immune responses and cellular senescence. Here, we examined effects of key cytokines linked to cellular senescence on expression of SARS‐CoV‐2 viral entry receptors. We found exposure of human umbilical vein endothelial cells (HUVECs) to the inflammatory cytokines, TNF‐α + IFN‐γ or a cocktail of TNF‐α + IFN‐γ + IL‐6, increased expression of ACE2/DPP4, accentuated the pro‐inflammatory senescence‐associated secretory phenotype (SASP), and decreased cellular proliferative capacity, consistent with progression towards a cellular senescence‐like state. IL‐6 by itself failed to induce substantial effects on viral entry receptors or SASP‐related genes, while synergy between TNF‐α and IFN‐γ initiated a positive feedback loop via hyper‐activation of the JAK/STAT1 pathway, causing SASP amplification. Breaking the interactive loop between senescence and cytokine secretion with JAK inhibitor ruxolitinib or antiviral drug remdesivir prevented hyper‐inflammation, normalized SARS‐CoV‐2 entry receptor expression, and restored HUVECs proliferative capacity. This loop appears to underlie cytokine‐mediated viral entry receptor activation and links with senescence and hyper‐inflammation.

Targeted long-read sequencing identifies missing pathogenic variants in unsolved Werner syndrome cases

BACKGROUND

Werner syndrome (WS) is an autosomal recessive progeroid syndrome caused by variants in WRN. The International Registry of Werner Syndrome has identified biallelic pathogenic variants in 179/188 cases of classical WS. In the remaining nine cases, only one heterozygous pathogenic variant has been identified.

METHODS

Targeted long-read sequencing (T-LRS) on an Oxford Nanopore platform was used to search for a second pathogenic variant in WRN. Previously, T-LRS was successfully used to identify missing variants and analyse complex rearrangements.

RESULTS

We identified a second pathogenic variant in eight of nine unsolved WS cases. In five cases, T-LRS identified intronic splice variants that were confirmed by either RT-PCR or exon trapping to affect splicing; in one case, T-LRS identified a 339 kbp deletion, and in two cases, pathogenic missense variants. Phasing of long reads predicted all newly identified variants were on a different haplotype than the previously known variant. Finally, in one case, RT-PCR previously identified skipping of exon 20; however, T-LRS did not detect a pathogenic DNA sequence variant.

CONCLUSION

T-LRS is an effective method for identifying missing pathogenic variants. Although limitations with computational prediction algorithms can hinder the interpretation of variants, T-LRS is particularly effective in identifying intronic variants.

DNA methylation signatures in Blood DNA of Hutchinson-Gilford Progeria syndrome

Hutchinson-Gilford Progeria Syndrome (HGPS) is an extremely rare genetic disorder caused by mutations in the LMNA gene and characterized by premature and accelerated aging beginning in childhood. In this study, we performed the first genome-wide methylation analysis on blood DNA of 15 patients with progeroid laminopathies using Infinium Methylation EPIC arrays including 8 patients with classical HGPS. We could observe DNA methylation alterations at 61 CpG sites as well as 32 significant regions following a 5 Kb tiling analysis. Differentially methylated probes were enriched for phosphatidylinositol biosynthetic process, phospholipid biosynthetic process, sarcoplasm, sarcoplasmic reticulum, phosphatase regulator activity, glycerolipid biosynthetic process, glycerophospholipid biosynthetic process, and phosphatidylinositol metabolic process. Differential methylation analysis at the level of promoters and CpG islands revealed no significant methylation changes in blood DNA of progeroid laminopathy patients. Nevertheless, we could observe significant methylation differences in classic HGPS when specifically looking at probes overlapping solo-WCGW partially methylated domains. Comparing aberrantly methylated sites in progeroid laminopathies, classic Werner syndrome, and Down syndrome revealed a common significantly hypermethylated region in close vicinity to the transcription start site of a long non-coding RNA located anti-sense to the Catenin Beta Interacting Protein 1 gene (CTNNBIP1). By characterizing epigenetically altered sites, we identify possible pathways/mechanisms that might have a role in the accelerated aging of progeroid laminopathies.

Werner syndrome in a Lebanese family

Werner syndrome (WS) is an extremely rare, autosomal recessive segmental progeroid disorder caused by biallelic pathogenic variants in the WRN, which encodes a multifunctional nuclear protein that belongs to the RecQ family of DNA helicases. Despite extensive research on WS in the last years, the population-specific mutational spectrum still needs to be elucidated. Moreover, there is an evident lack of detailed clinical descriptions accompanied with photographs of affected individuals. Here, we report a consanguineous Lebanese family in whom we identified a pathogenic homozygous nonsense variant c.1111G>T, p.Glu371* in the WRN. The index individual, at the age of 54 years, was suspected to have WS due to a history of early-onset cataracts, premature hair loss and graying, chronic nonhealing leg ulcers, Achilles' tendon calcifications, type 2 diabetes mellitus, dyslipidemia, hypothyroidism, and premature coronary artery disease. His four sisters, three of which deceased in the fifth decade, had clinical signs suggestive of WS. Moreover, his daughter, aged 23 years, had short stature, hair loss and flat feet. Taken together, we report a detailed clinical course of disease in several affected members of a consanguineous family, which is additionally documented by photographs.

A Novel Homozygous WRN Mutation Identified in a Middle Aged Man With Diabetes Mellitus Complicated By Multiple Features of Accelerated Aging

Background: Werner syndrome (WS; MIM# 277700) is a rare genetic disorder characterized by accelerated aging and predisposition to cancers. The causal gene, WRN, encodes a multifunctional nuclear protein that belongs to the RecQ family of DNA helicases. The earliest sign of WS is short stature due to the lack of pubertal growth spurt. In addition to the aged-appearance, WS patients typically develop functional declines of multiple organs including the endocrine system in their middle ages. Frequent Endocrine disorders include Type 2 Diabetes (T2D), dyslipidemia (DL), hypothyroidism, hypogonadism and osteoporosis. Most common causes of deaths are myocardial infarction and cancers in their 50s. Clinical Case: A 54-year old man was admitted for right wrist septic arthritis. His medical history was pertinent for premature cataract diagnosed in his 2^nd decade. He had uncontrolled T2D (peak HbA1C level 10%) since the age of 32 years, treated with oral hypoglycemics including glimepiride, sitagliptin and metformin then shifted to insulin over the past 2 years. He also had DL since the age of 41 years, characterized by hypertriglyceridemia (766 mg/dL) with very low HDL (7 mg/dL). At age 50, he was diagnosed with hypothyroidism and negative anti-TPO antibodies. Moreover, he had refractory bilateral leg ulcers that manifested at the age of 35 years requiring multiple debridments, premature coronary artery disease at the age of 38 years and ischemic cardiomyopathy. On examination, his height was 154 cm and weight 42 kgs. He had prominent eyes, a pinched nose, grey and sparse scalp hair with absence of eyebrows and eyelashes. Hoarse voice was easily noticeable. He had very thin limbs, flat feet, central fat distribution and muscle wasting. Skin was shiny, tight, and atrophic with overlying hypermelanosis. Old bilateral hyperkeratotic deep feet ulcers were noticed with variable necrosis. Blood chemistry testing showed: HbA1C 8.2%, disturbed lipid profile, TG 341 mg/dL, HDL 17 mg/dL, LDL 155 mg/dL, and TSH 21 µU/mL (0.2 - 4.2 µU/mL). MRI of the foot revealed Achilles’ tendon calcification. His parents were 2^nd degree cousins and had normal features. Three of his siblings had similar features and premature death. His diabetes was atypical due to his low BMI, high insulin requirements and the relatively early onset. WS was suspected based on the overall features of accelerated aging with characteristic deep leg ulcers and the family history. Genetic sequence analysis revealed a novel pathogenic homozygous nonsense variant mutation c.1111G>T, p.Glu371* of the WRN gene.

Conclusion: Werner syndrome is a rare genetic disease, but it carries high morbidity and mortality burden, in addition to impaired quality of life. It should be highly suspected in patients with atypical T2D, DL, premature coronary disease, refractory leg ulcers with features of accelerated aging and short stature.

Cell-to-Cell Variation in Gene Expression for Cultured Human Cells Is Controlled in Trans by Diverse Genes: Implications for the Pathobiology of Aging

Cell-to-cell variation in gene expression increases among homologous cells within multiple tissues during aging. We call this phenomenon variegated gene expression (VGE). Long, healthy life requires robust and coordinated gene expression. We posit that nature may have evolved VGE as a bet-hedging mechanism to protect reproductively active populations. The price we may pay is accelerated aging. That hypothesis will require the demonstration that genetic loci are capable of modulating degrees of VGE. While loci controlling VGE in yeast and genes controlling interindividual variation in gene expression in Caenorhabditis elegans have been identified, there has been no compelling evidence for the role of specific genetic loci in modulations of VGE of specific targets in humans. With the assistance of a core facility, we used a customized library of siRNA constructs to screen 1,195 human genes to identify loci contributing to the control of VGE of a gene with relevance to the biology of aging. We identified approximately 50 loci controlling VGE of the prolongevity gene, SIRT1. Because of its partial homology to FOXO3A, a variant of which is enriched in centenarians, our laboratory independently confirmed that the knockdown of FOXF2 greatly diminished VGE of SIRT1 but had little impact upon the VGE of WRN. While the role of these VGE-altering genes on aging in vivo remains to be determined, we hypothesize that some of these genes can be targeted to increase functionality during aging.

Review of How Genetic Research on Segmental Progeroid Syndromes Has Documented Genomic Instability as a Hallmark of Aging But Let Us Now Pursue Antigeroid Syndromes!

The purpose of this early contribution to the new Fellows Forum of this pioneering journal for what is now called Geroscience is to provide an example of how the author's interest in using the emerging tools of human genetics has led to strong support for one of the hallmarks of aging-Genomic Instability. We shall also briefly review our emerging interests in the genetic analysis of what we have called Antigeroid Syndromes. While there has been significant progress in that direction via genetic studies of centenarians, the search for genetic pathways that make individuals unusually resistant or resilient to the ravages of specific geriatric disorders has been comparatively neglected. We refer to these disorders as Unimodal Antigeroid Syndromes. It is our hope that our young colleagues will consider research efforts in that direction.

SMAD4 mutations and cross-talk between TGF-β/IFNγ signaling accelerate rates of DNA damage and cellular senescence, resulting in a segmental progeroid syndrome-the Myhre syndrome

SMAD4 encodes a member of the SMAD family of proteins involved in the TGF-β signaling pathway. Potentially heritable, autosomal dominant, gain-of-function heterozygous variants of SMAD4 cause a rare developmental disorder, the Myhre syndrome, which is associated with a wide range of developmental and post-developmental phenotypes that we now characterize as a novel segmental progeroid syndrome. Whole-exome sequencing of a patient referred to our International Registry of Werner Syndrome revealed a heterozygous p.Arg496Cys variant of the SMAD4 gene. To investigate the role of SMAD4 mutations in accelerated senescence, we generated cellular models overexpressing either wild-type SMAD4 or mutant SMAD4-R496C in normal skin fibroblasts. We found that cells expressing the SMAD4-R496C mutant exhibited decreased proliferation and elevated expression of cellular senescence and inflammatory markers, including IL-6, IFNγ, and a TGF-β target gene, PAI-1. Here we show that transient exposure to TGF-β, an inflammatory cytokine, followed by chronic IFNγ stimulation, accelerated rates of senescence that were associated with increased DNA damage foci and SMAD4 expression. TGF-β, IFNγ, or combinations of both were not sufficient to reduce proliferation rates of fibroblasts. In contrast, TGF-β alone was able to induce preadipocyte senescence via induction of the mTOR protein. The mTOR inhibitor rapamycin mitigated TGF-β-induced expression of p21, p16, and DNA damage foci and improved replicative potential of preadipocytes, supporting the cell-specific response to this cytokine. These findings collectively suggest that persistent DNA damage and cross-talk between TGF-β/IFNγ pathways contribute to a series of molecular events leading to cellular senescence and a segmental progeroid syndrome.

Multisystem Progeroid Syndrome With Lipodystrophy, Cardiomyopathy, and Nephropathy Due to an LMNA p.R349W Variant

Background

Pathogenic variants in lamin A/C (LMNA) cause a variety of progeroid disorders including Hutchinson-Gilford progeria syndrome, mandibuloacral dysplasia, and atypical progeroid syndrome. Six families with 11 patients harboring a pathogenic heterozygous LMNA c.1045C>T; p.R349W variant have been previously reported to have partial lipodystrophy, cardiomyopathy, and focal segmental glomerulosclerosis (FSGS), suggesting a distinct progeroid syndrome.

Methods

We report 6 new patients with a heterozygous LMNA p.R349W variant and review the phenotype of previously reported patients to define their unique characteristics. We also performed functional studies on the skin fibroblasts of a patient to seek the underlying mechanisms of various clinical manifestations.

Results

Of the total 17 patients, all 14 adults with the heterozygous LMNA p.R349W variant had peculiar lipodystrophy affecting the face, extremities, palms, and soles with variable gain of subcutaneous truncal fat. All of them had proteinuric nephropathy with FSGS documented in 7 of them. Ten developed cardiomyopathy, and 2 of them died early at ages 33 and 45 years. Other common features included premature graying, alopecia, high-pitched voice, micrognathia, hearing loss, and scoliosis. Metabolic complications, including diabetes mellitus, hypertriglyceridemia, and hepatomegaly, were highly prevalent. This variant did not show any abnormal splicing, and no abnormal nuclear morphology was noted in the affected fibroblasts.

Conclusions

The heterozygous LMNA p.R349W variant in affected individuals has several distinct phenotypic features, and these patients should be classified as having multisystem progeroid syndrome (MSPS). MSPS patients should undergo careful assessment at symptom onset and yearly metabolic, renal, and cardiac evaluation because hyperglycemia, hypertriglyceridemia, FSGS, and cardiomyopathy cause major morbidity and mortality.

Novel LMNA mutations in Greek and Myanmar Patients with Progeroid Features and Cardiac Manifestations

Segmental progeroid syndromes are groups of genetic disorders with multiple features resembling accelerated aging. The International Registry of Werner Syndrome (Seattle, WA) recruits pedigrees of progeroid syndromes from all over the world. We identified two novel LMNA mutations, p.Asp300Gly in a patient from Myanmar, and p.Asn466Lys, in a patient from Greece. Both were referred to our Registry for the genetic diagnosis because of the accelerated aged-appearance and cardiac complications. LMNA mutations are the second most common genetic cause of progeroid syndromes after WRN mutations in our Registry. As the next generation sequencing becomes readily available, we expect to identify more cases of rare genetic diseases in the developing countries.

A Case Report of Werner's Syndrome With a Novel Mutation From India

Werner's syndrome (WS) or progeria adultorum is a heritable autosomal recessive disease in which the aging process is accelerated, just after puberty. It is caused by mutations in the WRN gene, which encodes a member of the RECQ family of DNA helicases and has a role in DNA repair. WS is being more appropriately recognized as a condition in which the lack of WRN protein results in an overall decline in the normal physiological functions of various organs rather than premature aging. Here, we describe a rare case of WS with a novel mutation from India. Our patient was an adult male with a history of growth arrest since puberty and other clinical features such as sclerodermatous skin changes, premature graying and thinning of hair, bilateral cataract, a single non-healing ulcer, hypothyroidism, underdeveloped secondary sexual characters with hypogonadism, infertility, squeaky voice, and early signs of arteriosclerosis. On genetic analysis, he was found to have a homozygous pathogenic variant c.3190C>T in exon 26 of the WRN gene, which has never been reported in WS.

Inactivating Mutations in Exonuclease and Polymerase Domains in DNA Polymerase Delta Alter Sensitivities to Inhibitors of dNTP Synthesis

POLD1 encodes the catalytic subunit of DNA polymerase delta (Polδ), the major lagging strand polymerase, which also participates in DNA repair. Mutations affecting the exonuclease domain increase the risk of various cancers, while mutations that change the polymerase active site cause a progeroid syndrome called mandibular hypoplasia, deafness, progeroid features, and lipodystrophy (MDPL) syndrome. We generated a set of catalytic subunit of human telomerase (hTERT)-immortalized human fibroblasts expressing wild-type or mutant POLD1 using the retroviral LXSN vector system. In the resulting cell lines, expression of endogenous POLD1 was suppressed in favor of the recombinant POLD1. The siRNA screening of DNA damage-related genes revealed that fibroblasts expressing D316H and S605del POLD1 were more sensitive to knockdowns of ribonuclease reductase (RNR) components, RRM1 and RRM2 in the presence of hydroxyurea (HU), an RNR inhibitor. On the contrary, SAMHD1 siRNA, which increases the concentration of dNTPs, increased growth of wild type, D316H, and S605del POLD1 fibroblasts. Hypersensitivity to dNTP synthesis inhibition in POLD1 mutant lines was confirmed using gemcitabine. Our finding is consistent with the notion that reduced dNTP concentration negatively affects the cell growth of hTERT fibroblasts expressing exonuclease and polymerase mutant POLD1.

Epigenetic signatures of Werner syndrome occur early in life and are distinct from normal epigenetic aging processes

Werner Syndrome (WS) is an adult-onset segmental progeroid syndrome. Bisulfite pyrosequencing of repetitive DNA families revealed comparable blood DNA methylation levels between classical (18 WRN-mutant) or atypical WS (3 LMNA-mutant and 3 POLD1-mutant) patients and age- and sex-matched controls. WS was not associated with either age-related accelerated global losses of ALU, LINE1, and α-satellite DNA methylations or gains of rDNA methylation. Single CpG methylation was analyzed with Infinium MethylationEPIC arrays. In a correspondence analysis, atypical WS samples clustered together with the controls and were clearly separated from classical WS, consistent with distinct epigenetic pathologies. In classical WS, we identified 659 differentially methylated regions (DMRs) comprising 3,656 CpG sites and 613 RefSeq genes. The top DMR was located in the HOXA4 promoter. Additional DMR genes included LMNA, POLD1, and 132 genes which have been reported to be differentially expressed in WRN-mutant/depleted cells. DMRs were enriched in genes with molecular functions linked to transcription factor activity and sequence-specific DNA binding to promoters transcribed by RNA polymerase II. We propose that transcriptional misregulation of downstream genes by the absence of WRN protein contributes to the variable premature aging phenotypes of WS. There were no CpG sites showing significant differences in DNA methylation changes with age between WS patients and controls. Genes with both WS- and age-related methylation changes exhibited a constant offset of methylation between WRN-mutant patients and controls across the entire analyzed age range. WS-specific epigenetic signatures occur early in life and do not simply reflect an acceleration of normal epigenetic aging processes.

Epigenetic clock for skin and blood cells applied to Hutchinson Gilford Progeria Syndrome and ex vivo studies

DNA methylation (DNAm)-based biomarkers of aging have been developed for many tissues and organs. However, these biomarkers have sub-optimal accuracy in fibroblasts and other cell types used in ex vivo studies. To address this challenge, we developed a novel and highly robust DNAm age estimator (based on 391 CpGs) for human fibroblasts, keratinocytes, buccal cells, endothelial cells, lymphoblastoid cells, skin, blood, and saliva samples. High age correlations can also be observed in sorted neurons, glia, brain, liver, and even bone samples. Gestational age correlates with DNAm age in cord blood. When used on fibroblasts from Hutchinson Gilford Progeria Syndrome patients, this age estimator (referred to as the skin & blood clock) uncovered an epigenetic age acceleration with a magnitude that is below the sensitivity levels of other DNAm-based biomarkers. Furthermore, this highly sensitive age estimator accurately tracked the dynamic aging of cells cultured ex vivo and revealed that their proliferation is accompanied by a steady increase in epigenetic age. The skin & blood clock predicts lifespan and it relates to many age-related conditions. Overall, this biomarker is expected to become useful for forensic applications (e.g. blood or buccal swabs) and for a quantitative ex vivo human cell aging assay.

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.

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.

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.

Accelerated epigenetic aging in Werner syndrome

Individuals suffering from Werner syndrome (WS) exhibit many clinical signs of accelerated aging. While the underlying constitutional mutation leads to accelerated rates of DNA damage, it is not yet known whether WS is also associated with an increased epigenetic age according to a DNA methylation based biomarker of aging (the "Epigenetic Clock"). Using whole blood methylation data from 18 WS cases and 18 age matched controls, we find that WS is associated with increased extrinsic epigenetic age acceleration (p=0.0072) and intrinsic epigenetic age acceleration (p=0.04), the latter of which is independent of age-related changes in the composition of peripheral blood cells. A multivariate model analysis reveals that WS is associated with an increase in DNA methylation age (on average 6.4 years, p=0.011) even after adjusting for chronological age, gender, and blood cell counts. Further, WS might be associated with a reduction in naïve CD8+ T cells (p=0.025) according to imputed measures of blood cell counts. Overall, this study shows that WS is associated with an increased epigenetic age of blood cells which is independent of changes in blood cell composition. The extent to which this alteration is a cause or effect of WS disease phenotypes remains unknown.

ERCC4 variants identified in a cohort of patients with segmental progeroid syndromes

Pathogenic variants in genes, which encode DNA repair and damage response proteins, result in a number of genomic instability syndromes with features of accelerated aging. ERCC4 (XPF) encodes a protein that forms a complex with ERCC1 and is required for the 5' incision during nucleotide excision repair. ERCC4 is also FANCQ, illustrating a critical role in interstrand crosslink repair. Pathogenic variants in this gene cause xeroderma pigmentosum, XFE progeroid syndrome, Cockayne syndrome (CS), and Fanconi anemia. We performed massive parallel sequencing for 42 unsolved cases submitted to the International Registry of Werner Syndrome. Two cases, each carrying two novel heterozygous ERCC4 variants, were identified. The first case was a compound heterozygote for: c.2395C > T (p.Arg799Trp) and c.388+1164_792+795del (p.Gly130Aspfs*18). Further molecular and cellular studies indicated that the ERCC4 variants in this patient are responsible for a phenotype consistent with a variant of CS. The second case was heterozygous for two variants in cis: c.[1488A > T; c.2579C > A] (p.[Gln496His; Ala860Asp]). While the second case also had several phenotypic features of accelerated aging, we were unable to provide biological evidence supporting the pathogenic roles of the associated ERCC4 variants. Precise genetic causes and disease mechanism of the second case remains to be determined.

Dysfunction of the MDM2/p53 axis is linked to premature aging

The tumor suppressor p53, a master regulator of the cellular response to stress, is tightly regulated by the E3 ubiquitin ligase MDM2 via an autoregulatory feedback loop. In addition to its well-established role in tumorigenesis, p53 has also been associated with aging in mice. Several mouse models with aberrantly increased p53 activity display signs of premature aging. However, the relationship between dysfunction of the MDM2/p53 axis and human aging remains elusive. Here, we have identified an antiterminating homozygous germline mutation in MDM2 in a patient affected by a segmental progeroid syndrome. We show that this mutation abrogates MDM2 activity, thereby resulting in enhanced levels and stability of p53. Analysis of the patient's primary cells, genome-edited cells, and in vitro and in vivo analyses confirmed the MDM2 mutation's aberrant regulation of p53 activity. Functional data from a zebrafish model further demonstrated that mutant Mdm2 was unable to rescue a p53-induced apoptotic phenotype. Altogether, our findings indicate that mutant MDM2 is a likely driver of the observed segmental form of progeria.

Werner syndrome: Clinical features, pathogenesis and potential therapeutic interventions

Werner syndrome (WS) is a prototypical segmental progeroid syndrome characterized by multiple features consistent with accelerated aging. It is caused by null mutations of the WRN gene, which encodes a member of the RECQ family of DNA helicases. A unique feature of the WRN helicase is the presence of an exonuclease domain in its N-terminal region. Biochemical and cell biological studies during the past decade have demonstrated involvements of the WRN protein in multiple DNA transactions, including DNA repair, recombination, replication and transcription. A role of the WRN protein in telomere maintenance could explain many of the WS phenotypes. Recent discoveries of new progeroid loci found in atypical Werner cases continue to support the concept of genomic instability as a major mechanism of biological aging. Based on these biological insights, efforts are underway to develop therapeutic interventions for WS and related progeroid syndromes.

High incidence of BSCL2 intragenic recombinational mutation in Peruvian type 2 Berardinelli-Seip syndrome

Congenital generalized lipodystrophy (CGL) is a genetically heterogeneous group of disorders characterized by the absence of functional adipose tissue. We identified two pedigrees with CGL in the community of the Mestizo tribe in the northern region of Peru. Five cases, ranging from 15 months to 7 years of age, presented with generalized lipodystrophy, muscular prominence, mild intellectual disability, and a striking aged appearance. Sequencing of the BSCL2 gene, known to be mutated in type 2 CGL (CGL2; Berardinelli-Seip syndrome), revealed a homozygous deletion of exon 3 in all five patients examined, suggesting the presence of a founder mutation. This intragenic deletion appeared to be mediated by recombination between Alu sequences in introns 2 and 3. CGL2 in this population is likely underdiagnosed and undertreated because of its geographical, socio-economic, and cultural isolation.© 2016 Wiley Periodicals, Inc.

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

Werner syndrome (WS) is a rare autosomal recessive disorder characterized by a constellation of adult onset phenotypes consistent with an acceleration of intrinsic biological aging. It is caused by pathogenic variants in the WRN gene, which encodes a multifunctional nuclear protein with exonuclease and helicase activities. WRN protein is thought to be involved in optimization of various aspects of DNA metabolism, including DNA repair, recombination, replication, and transcription. In this update, we summarize a total of 83 different WRN mutations, including eight previously unpublished mutations identified by the International Registry of Werner Syndrome (Seattle, WA) and the Japanese Werner Consortium (Chiba, Japan), as well as 75 mutations already reported in the literature. The Seattle International Registry recruits patients from all over the world to investigate genetic causes of a wide variety of progeroid syndromes in order to contribute to the knowledge of basic mechanisms of human aging. Given the unusually high prevalence of WS patients and heterozygous carriers in Japan, the major goal of the Japanese Consortium is to develop effective therapies and to establish management guidelines for WS patients in Japan and elsewhere. This review will also discuss potential translational approaches to this disorder, including those currently under investigation.

Werner syndrome through the lens of tissue and tumour genomics

Werner syndrome (WS) is the canonical adult human progeroid ('premature aging') syndrome. Patients with this autosomal recessive Mendelian disorder display constitutional genomic instability and an elevated risk of important age-associated diseases including cancer. Remarkably few analyses of WS patient tissue and tumors have been performed to provide insight into WS disease pathogenesis or the high risk of neoplasia. We used autopsy tissue from four mutation-typed WS patients to characterize pathologic and genomic features of WS, and to determine genomic features of three neoplasms arising in two of these patients. The results of these analyses provide new information on WS pathology and genomics; provide a first genomic characterization of neoplasms arising in WS; and provide new histopathologic and genomic data to test several popular models of WS disease pathogenesis.

How Research on Human Progeroid and Antigeroid Syndromes Can Contribute to the Longevity Dividend Initiative

Although translational applications derived from research on basic mechanisms of aging are likely to enhance health spans and life spans for most of us (the longevity dividend), there will remain subsets of individuals with special vulnerabilities. Medical genetics is a discipline that describes such "private" patterns of aging and can reveal underlying mechanisms, many of which support genomic instability as a major mechanism of aging. We review examples of three classes of informative disorders: "segmental progeroid syndromes" (those that appear to accelerate multiple features of aging), "unimodal progeroid syndromes" (those that impact on a single disorder of aging), and "unimodal antigeroid syndromes," variants that provide enhanced protection against specific disorders of aging; we urge our colleagues to expand our meager research efforts on the latter, including ancillary somatic cell genetic approaches.

The Werner syndrome RECQ helicase targets G4 DNA in human cells to modulate transcription

The Werner syndrome (WS) is a prototypic adult Mendelian progeroid syndrome in which signs of premature aging are associated with genomic instability and an elevated risk of cancer. The WRN RECQ helicase protein binds and unwinds G-quadruplex (G4) DNA substrates in vitro, and we identified significant enrichment in G4 sequence motifs at the transcription start site and 5' ends of first introns (false discovery rate < 0.001) of genes down-regulated in WS patient fibroblasts. This finding provides strong evidence that WRN binds G4 DNA structures at many chromosomal sites to modulate gene expression. WRN appears to bind a distinct subpopulation of G4 motifs in human cells, when compared with the related Bloom syndrome RECQ helicase protein. Functional annotation of the genes and miRNAs altered in WS provided new insight into WS disease pathogenesis. WS patient fibroblasts displayed altered expression of multiple, mechanistically distinct, senescence-associated gene expression programs, with altered expression of disease-associated miRNAs, and dysregulation of canonical pathways that regulate cell signaling, genome stability and tumorigenesis. WS fibroblasts also displayed a highly statistically significant and distinct gene expression signature, with coordinate overexpression of nearly all of the cytoplasmic tRNA synthetases and associated ARS-interacting multifunctional protein genes. The 'non-canonical' functions of many of these upregulated tRNA charging proteins may together promote WS disease pathogenesis. Our results identify the human WRN RECQ protein as a G4 helicase that modulates gene expression in G4-dependent fashion at many chromosomal sites and provide several new and unexpected mechanistic insights into WS disease pathogenesis.

Aβ 1-40 enhances the proliferation of human diploid fibroblasts

There is a vast literature on the role of beta amyloid (Aβ) peptides in the pathogenesis of Alzheimer's disease. However, there is a paucity of research on the potential physiological functions of these evolutionarily conserved products of the Aβ precursor protein. Based on previous studies in neuroblastoma cells, we hypothesized that Aβ may contribute to the proliferation of somatic cells. We present evidence supporting this hypothesis for the case of cultured human skin fibroblasts immortalized with the catalytic subunit of human telomerase (hTERT). Optimal concentrations ranged from 100 pM-10 nM, depending on the nature of the assay.

POLD1 Germline Mutations in Patients Initially Diagnosed with Werner Syndrome

Segmental progeroid syndromes are rare, heterogeneous disorders characterized by signs of premature aging affecting more than one tissue or organ. A prototypic example is the Werner syndrome (WS), caused by biallelic germline mutations in the Werner helicase gene (WRN). While heterozygous lamin A/C (LMNA) mutations are found in a few nonclassical cases of WS, another 10%-15% of patients initially diagnosed with WS do not have mutations in WRN or LMNA. Germline POLD1 mutations were recently reported in five patients with another segmental progeroid disorder: mandibular hypoplasia, deafness, progeroid features syndrome. Here, we describe eight additional patients with heterozygous POLD1 mutations, thereby substantially expanding the characterization of this new example of segmental progeroid disorders. First, we identified POLD1 mutations in patients initially diagnosed with WS. Second, we describe POLD1 mutation carriers without clinically relevant hearing impairment or mandibular underdevelopment, both previously thought to represent obligate diagnostic features. These patients also exhibit a lower incidence of metabolic abnormalities and joint contractures. Third, we document postnatal short stature and premature greying/loss of hair in POLD1 mutation carriers. We conclude that POLD1 germline mutations can result in a variably expressed and probably underdiagnosed segmental progeroid syndrome.

Truncated prelamin A expression in HGPS-like patients: a transcriptional study

Premature aging syndromes are rare genetic disorders mimicking clinical and molecular features of aging. A recently identified group of premature aging syndromes is linked to mutation of the LMNA gene encoding lamins A and C, and is associated with nuclear deformation and dysfunction. Hutchinson-Gilford progeria syndrome (HGPS) was the first premature aging syndrome linked to LMNA mutation and its molecular bases have been deeply investigated. It is due to a recurrent de novo mutation leading to aberrant splicing and the production of a truncated and toxic nuclear lamin A precursor (prelamin AΔ50), also called progerin. In this work and based on the literature data, we propose to distinguish two main groups of premature aging laminopathies: (1) HGPS and HGP-like syndromes, which share clinical features due to hampered processing and intranuclear toxic accumulation of prelamin A isoforms; and (2) APS (atypical progeria syndromes), due to dominant or recessive missense mutations affecting lamins A and C. Among HGPS-like patients, several deleted prelamin A transcripts (prelamin AΔ50, AΔ35 and AΔ90) have been described. The purpose of this work was to characterize those transcripts in eight patients affected with HGP-like rare syndromes. When fibroblasts were available, the relationships between the presence and ratios of these transcripts and other parameters were studied, aiming to increase our understanding of genotype-phenotype relationships in HGPS-like patients. Altogether our results evidence that progerin accumulation is the major pathogenetic mechanism responsible for HGP-like syndromes due to mutations near the donor splice site of exon 11.

Genetic diversity is a predictor of mortality in humans

Background

It has been well-established, both by population genetics theory and direct observation in many organisms, that increased genetic diversity provides a survival advantage. However, given the limitations of both sample size and genome-wide metrics, this hypothesis has not been comprehensively tested in human populations. Moreover, the presence of numerous segregating small effect alleles that influence traits that directly impact health directly raises the question as to whether global measures of genomic variation are themselves associated with human health and disease.

Results

We performed a meta-analysis of 17 cohorts followed prospectively, with a combined sample size of 46,716 individuals, including a total of 15,234 deaths. We find a significant association between increased heterozygosity and survival (P = 0.03). We estimate that within a single population, every standard deviation of heterozygosity an individual has over the mean decreases that person’s risk of death by 1.57%.

Conclusions

This effect was consistent between European and African ancestry cohorts, men and women, and major causes of death (cancer and cardiovascular disease), demonstrating the broad positive impact of genomic diversity on human survival.

Electronic supplementary material

The online version of this article (doi:10.1186/s12863-014-0159-7) contains supplementary material, which is available to authorized users.

Atypical Aicardi-Goutieres syndrome: is the WRN locus a modifier?

We describe a 28-year-old Turkish man with consanguineous parents who presented with an aged appearance with prematurely gray hair and scleroderma-like skin, spastic paraplegia, and apparent disability. The proband and each of his parents were heterozygous for a mutation in WRN, which could not explain his symptoms. Exome sequencing of the proband's blood DNA showed a homozygous c.626-1G > C mutation in intron 5 of the SAMHD1 gene, which encodes a triphosphohydrolase involved in the regulation of intracellular dNTP pools and which is mutated in Aicardi-Goutieres syndrome. The RNA studies confirmed aberrant splicing of exon 6, and family studies showed that both parents are heterozygous for this mutation. We conclude that mutations in SAMHD1 - in addition to causing an early-onset form of encephalopathy in Aicardi-Goutieres syndrome - may present with modest signs of accelerated aging similar to Werner syndrome. The extent to which heterozygosity at the WRN locus may modify the effect of biallelic SAMHD1 mutations is unknown. It is conceivable that synergistic effects of these two mutations might be responsible for the unusual phenotype.

Rapamycin decreases DNA damage accumulation and enhances cell growth of WRN-deficient human fibroblasts

Werner syndrome (WS), caused by mutations at the WRN helicase gene, is a progeroid syndrome characterized by multiple features consistent with accelerated aging. Aberrant double-strand DNA damage repair leads to genomic instability and reduced replicative lifespan of somatic cells. We observed increased autophagy in WRN knockdown cells; this was further increased by short-term rapamycin treatment. Long-term rapamycin treatment resulted in improved growth rate, reduced accumulation of DNA damage foci and improved nuclear morphology; autophagy markers were reduced to near-normal levels, possibly due to clearance of damaged proteins. These data suggest that protein aggregation plays a role in the development of WS phenotypes and that the mammalian target of rapamycin complex 1 pathway is a potential therapeutic target of WS.

Search and insights into novel genetic alterations leading to classical and atypical Werner syndrome

Segmental progeroid syndromes are a group of disorders with multiple features resembling accelerated aging. Adult-onset Werner syndrome (WS) and childhood-onset Hutchinson-Gilford progeria syndrome are the best known examples. The discovery of genes responsible for such syndromes has facilitated our understanding of the basic mechanisms of aging as well as the pathogenesis of other common, age-related diseases. Our International Registry of Werner Syndrome accesses progeroid pedigrees from all over the world, including those for whom we have ruled out a mutation at the WRN locus. Cases without WRN mutations are operationally categorized as 'atypical WS' (AWS). In 2003, we identified LMNA mutations among a subset of AWS cases using a candidate gene approach. As of 2013, the Registry has 142 WS patients with WRN mutations, 11 AWS patients with LMNA mutations, and 49 AWS patients that have neither WRN nor LMNA mutations. Efforts are underway to identify the responsible genes for AWS with unknown genetic causes. While WS and AWS are rare disorders, the causative genes have been shown to have much wider implications for cancer, cardiovascular disease and the biology of aging. Remarkably, centenarian studies revealed WRN and LMNA polymorphic variants among those who have escaped various geriatric disorders.

DNA damage accumulation and TRF2 degradation in atypical Werner syndrome fibroblasts with LMNA mutations

Segmental progeroid syndromes are groups of disorders with multiple features suggestive of accelerated aging. One subset of adult-onset progeroid syndromes, referred to as atypical Werner syndrome, is caused by mutations in the LMNA gene, which encodes a class of nuclear intermediate filaments, lamin A/C. We previously described rapid telomere attrition and accelerated replicative senescence in cultured fibroblasts overexpressing mutant lamin A. In this study, we investigated the cellular phenotypes associated with accelerated telomere shortening in LMNA mutant primary fibroblasts. In early passage primary fibroblasts with R133L or L140R LMNA mutations, shelterin protein components were already reduced while cells still retained telomere lengths comparable to those of controls. There was a significant inverse correlation between the degree of abnormal nuclear morphology and the level of TRF2, a shelterin subunit, suggesting a potential causal relationship. Stabilization of the telomeres via the introduction of the catalytic subunit of human telomerase, hTERT (human telomerase reverse transcriptase), did not prevent degradation of shelterin components, indicating that reduced TRF2 in LMNA mutants is not mediated by short telomeres. Interestingly, γ-H2AX foci (reflecting double strand DNA damage) in early passage LMNA mutant primary fibroblasts and LMNA mutant hTERT fibroblasts were markedly increased in non-telomeric regions of DNA. Our results raise the possibility that mutant lamin A/C causes global genomic instability with accumulation of non-telomeric DNA damage as an early event, followed by TRF2 degradation and telomere shortening.

Functional deficit associated with a missense Werner syndrome mutation

Werner syndrome (WS) is a rare autosomal recessive disorder caused by mutations in the WRN gene. WRN helicase, a member of the RecQ helicase family, is involved in various DNA metabolic pathways including DNA replication, recombination, DNA repair and telomere maintenance. In this study, we have characterized the G574R missense mutation, which was recently identified in a WS patient. Our biochemical experiments with purified mutant recombinant WRN protein showed that the G574R mutation inhibits ATP binding, and thereby leads to significant decrease in helicase activity. Exonuclease activity of the mutant protein was not significantly affected, whereas its single strand DNA annealing activity was higher than that of wild type. Deficiency in the helicase activity of the mutant may cause defects in replication and other DNA metabolic processes, which in turn could be responsible for the Werner syndrome phenotype in the patient. In contrast to the usual appearance of WS, the G574R patient has normal stature. Thus the short stature normally associated with WS may not be due to helicase deficiency.

Ethnic-Specific WRN Mutations in South Asian Werner Syndrome Patients: Potential Founder Effect in Patients with Indian or Pakistani Ancestry

Werner syndrome is a rare autosomal recessive disorder characterized by multiple features consistent with accelerated aging. It is caused by mutations in the WRN gene, which encodes a RecQ type helicase. To date, more than 70 disease-causing mutations have been reported. While founder mutations and a corresponding relatively high incidence of WS have been reported in Japan and Sardinia, such mutations have not been previously described among patients of South Asian descent. Here we report two novel WRN mutations in three pedigrees. A homozygous c.561A>G mutation in exon 6 was identified both in a pedigree from Kerala, India and in a British patient of Pakistani ancestry. Although c.561A>G does not alter the corresponding amino acid (p.K187K), it creates a cryptic splice site resulting in a 98bp deletion at the mRNA level (r.557-654del98) followed by a frameshift (p.K187fs). These two cases shared the same haplotype across the WRN gene, and were distinct from another Indian Werner patient with a homozygous stop codon mutation, c.2855 C>A (p.S952*) in exon 24. As the Indian population increases and the awareness of Werner syndrome grows, we anticipate that more cases will be identified with these founder mutations among South Asian Werner syndrome patients.