Higher order chromatin structure at the X-inactivation center via looping DNA

In mammals, the silencing step of the X-chromosome inactivation (XCI) process is initiated by the non-coding Xist RNA. Xist is known to be controlled by the non-coding Xite and Tsix loci, but the mechanisms by which Tsix and Xite regulate Xist are yet to be fully elucidated. Here, we examine the role of higher order chromatin structure across the 100-kb region of the mouse X-inactivation center (Xic) and map domains of specialized chromatin in vivo. By hypersensitive site mapping and chromosome conformation capture (3C), we identify two domains of higher order chromatin structure. Xite makes looping interactions with Tsix, while Xist makes contacts with Jpx/Enox, another non-coding gene not previously implicated in XCI. These regions interact in a developmentally-specific and sex-specific manner that is consistent with a regulatory role in XCI. We propose that dynamic changes in three-dimensional architecture leads to formation of separate chromatin hubs in Tsix and Xist that together regulate the initiation of X-chromosome inactivation.

Dosage compensation in the mouse balances up-regulation and silencing of X-linked genes

Dosage compensation in mammals involves silencing of one X chromosome in XX females and requires expression, in cis, of Xist RNA. The X to be inactivated is randomly chosen in cells of the inner cell mass (ICM) at the blastocyst stage of development. Embryonic stem (ES) cells derived from the ICM of female mice have two active X chromosomes, one of which is inactivated as the cells differentiate in culture, providing a powerful model system to study the dynamics of X inactivation. Using microarrays to assay expression of X-linked genes in undifferentiated female and male mouse ES cells, we detect global up-regulation of expression (1.4- to 1.6-fold) from the active X chromosomes, relative to autosomes. We show a similar up-regulation in ICM from male blastocysts grown in culture. In male ES cells, up-regulation reaches 2-fold after 2–3 weeks of differentiation, thereby balancing expression between the single X and the diploid autosomes. We show that silencing of X-linked genes in female ES cells occurs on a gene-by-gene basis throughout differentiation, with some genes inactivating early, others late, and some escaping altogether. Surprisingly, by allele-specific analysis in hybrid ES cells, we also identified a subgroup of genes that are silenced in undifferentiated cells. We propose that X-linked genes are silenced in female ES cells by spreading of Xist RNA through the X chromosome territory as the cells differentiate, with silencing times for individual genes dependent on their proximity to the Xist locus.

In organisms such as fruit flies and humans, major chromosomal differences exist between the sexes: females have two large, gene-rich X chromosomes, and males have one X and one small, gene-poor Y. Various strategies have evolved to balance X-linked gene expression between the single X and the autosomes, and between the sexes (a phenomenon called dosage compensation). In Drosophila melanogaster, expression from the male X is up-regulated approximately 2-fold, thereby balancing both X-to-autosome and female-to-male expression. In contrast, mammals silence one of the two female Xs in a process requiring the untranslated RNA product of the Xist gene. This balances female-to-male expression but leaves both sexes with only one functional X chromosome. Using mouse embryonic stem cells and microarray expression analysis, we found that dosage compensation in mice is more complex than previously thought, with X-linked genes up-regulated in both male and female cells so as to balance X-to-autosome expression. As differentiation proceeds, female cells show progressive loss of expression from one of the two initially active Xs. Surprisingly, silencing occurs on a gene-by-gene basis over 2–3 week of differentiation; some genes escape altogether, whereas a subgroup of genes, often adjacent to the Xist locus, is silenced even in undifferentiated cells. We propose that female X-linked genes are silenced by progressive spreading of Xist RNA through the X chromosome territory as differentiation proceeds.

In mouse embryonic stem cells, X:autosome expression balance is achieved by up-regulating X-linked genes in both sexes and gene-by-gene silencing on one female X chromosome.

Tuning certainty factor and local weight of fuzzy production rules by using fuzzy neural network

Approximate reasoning in a fuzzy system is concerned with inferring an approximate conclusion from fuzzy and vague inputs. There are many ways in which different forms of conclusions can be drawn. Fuzzy sets are usually represented by fuzzy membership functions. These membership functions are assumed to have a clearly defined base. For other fuzzy sets such as intelligent, smart, or beautiful, etc., it would be difficult to define clearly its base because its base may consist of several other fuzzy sets or unclear nonfuzzy bases. A method to handle this kind of fuzzy set is proposed. A fuzzy neural network (FNN) is also proposed to tune knowledge representation parameters (KRPs). The contributions are that we are able to handle a broader range of fuzzy sets and build more powerful fuzzy systems so that the conclusions drawn are more meaningful, reliable, and accurate. An experiment is presented to demonstrate how our method works.

Evidence that homologous X-chromosome pairing requires transcription and Ctcf protein

X-chromosome inactivation (XCI) ensures the equality of X-chromosome dosages in male and female mammals by silencing one X in the female. To achieve the mutually exclusive designation of active X (Xa) and inactive X (Xi), the process necessitates that two Xs communicate in trans through homologous pairing. Pairing depends on a 15-kb region within the genes Tsix and Xite. Here, we dissect molecular requirements and find that pairing can be recapitulated by 1- to 2-kb subfragments of Tsix or Xite with little sequence similarity. However, a common denominator among them is the presence of the protein Ctcf, a chromatin insulator that we find to be essential for pairing. By contrast, the Ctcf-interacting partner, Yy1 (ref. 8), is not required. Pairing also depends on transcription. Transcriptional inhibition prevents new pair formation but does not perturb existing pairs. The kinetics suggest a pairing half-life of <1 h. We propose that pairing requires Ctcf binding and co-transcriptional activity of Tsix and Xite.

X-chromosome kiss and tell: how the Xs go their separate ways

Loci associated with noncoding RNAs have important roles in X-chromosome inactivation (XCI), the dosage compensation mechanism by which one of two X chromosomes in female cells becomes transcriptionally silenced. The Xs start out as epigenetically equivalent chromosomes, but XCI requires a cell to treat two identical X chromosomes in completely different ways: One X chromosome must remain transcriptionally active while the other becomes repressed. In the embryo of eutherian mammals, the choice to inactivate the maternal or paternal X chromosome is random. The fact that the Xs always adopt opposite fates hints at the existence of a trans-sensing mechanism to ensure the mutually exclusive silencing of one of the two Xs. This paper highlights recent evidence supporting a model for mutually exclusive choice that involves homologous chromosome pairing and the placement of asymmetric chromatin marks on the two Xs.

Weight loss during chronic, cervical vagus nerve stimulation in depressed patients with obesity: an observation

Fourteen patients were treated over 2 years with cervical vagus nerve stimulation (VNS) for adjunctive therapy of severe, treatment-resistant depression. Here, we report the serendipitous observation that this treatment was associated with highly significant, gradual weight loss despite the patients' report of not dieting or exercising. The weight loss was proportional to the initial BMI, that is, the more severe the obesity, the greater the weight loss. Weight loss did not correlate with changes in mood symptoms. The vagus nerve carries visceral information to and from the brain; modulation of its activity may alter eating behavior. Chronic cervical VNS may merit controlled study for the treatment of severe obesity.

Safety of aerosolized liposomal versus deoxycholate amphotericin B formulations for prevention of invasive fungal infections following lung transplantation: a retrospective study

BACKGROUND

Nebulized amphotericin B deoxycholate (AmBd) has been used to prevent invasive pulmonary aspergillosis after lung transplantation.

METHODS

In this retrospective study we compared the safety and tolerability of nebulized AmBd and nebulized liposomal amphotericin B (L-AmB) in 38 consecutive lung transplant recipients. Progress notes, medication administration records, microbiology, and pulmonary function reports were reviewed. Histologic sections from lung tissue were examined. Plasma amphotericin B levels were measured.

RESULTS

A total of 1206 doses of AmBd and 1149 doses of L-AmB were administered. Eighteen patients received AmBd only, 11 received L-AmB only, and 9 received the medications sequentially. The total number of complaints vs. the number of doses administered was 1.0% for AmBd-treated patients and 1.2% for L-AmB-treated patients. No differences were observed between the treatment groups on lung biopsy specimens. Plasma amphotericin B levels were <0.2-0.9 microg/mL in AmBd-treated patients and <0.2 microg/mL in L-AmB-treated patients.

CONCLUSIONS

In lung transplant recipients, both inhaled AmBd and L-AmB were safe and well tolerated over a large number of medication exposures.

Sex chromosome silencing in the marsupial male germ line

In marsupials, dosage compensation involves silencing of the father's X-chromosome. Because no XIST orthologue has been found, how imprinted X-inactivation occurs is unknown. In eutherians, the X is subject to meiotic sex chromosome inactivation (MSCI) in the paternal germ line and persists thereafter as postmeiotic sex chromatin (PMSC). One hypothesis proposes that the paternal X is inherited by the eutherian zygote as a preinactive X and raises the possibility of a similar process in the marsupial germ line. Here we demonstrate that MSCI and PMSC occur in the opossum. Surprisingly, silencing occurs before X-Y association. After MSCI, the X and Y fuse through a dense plate without obvious synapsis. Significantly, sex chromosome silencing continues after meiosis, with the opossum PMSC sharing features of eutherian PMSC. These results reveal a common gametogenic program in two diverse clades of mammals and support the idea that male germ-line silencing may have provided an ancestral form of mammalian dosage compensation.

Perinucleolar Targeting of the Inactive X during S Phase: Evidence for a Role in the Maintenance of Silencing

In mammalian females, two X chromosomes are epigenetically distinguished as active and inactive chromosomes to balance X-linked gene dosages between males and females. How the Xs are maintained differently in the same nucleus remains unknown. Here, we demonstrate that the inactive X (Xi) is targeted to a distinct nuclear compartment following pairing with its homologous partner. During mid-to-late S phase, 80%-90% of Xi contact the nucleolus and reside within a Snf2h-enriched ring. Autosomes carrying ectopic X-inactivation center sequences are also targeted to the perinucleolar compartment. Deleting Xist results in a loss of nucleolar association and an inability to maintain Xi heterochromatin, leading to Xi reactivation at the single gene level. We propose that the Xi must continuously visit the perinucleolar compartment to maintain its epigenetic state. These data raise a mechanism by which chromatin states can be replicated by spatial and temporal separation in the nucleus.

Genome of the marsupial Monodelphis domestica reveals innovation in non-coding sequences

We report a high-quality draft of the genome sequence of the grey, short-tailed opossum (Monodelphis domestica). As the first metatherian ('marsupial') species to be sequenced, the opossum provides a unique perspective on the organization and evolution of mammalian genomes. Distinctive features of the opossum chromosomes provide support for recent theories about genome evolution and function, including a strong influence of biased gene conversion on nucleotide sequence composition, and a relationship between chromosomal characteristics and X chromosome inactivation. Comparison of opossum and eutherian genomes also reveals a sharp difference in evolutionary innovation between protein-coding and non-coding functional elements. True innovation in protein-coding genes seems to be relatively rare, with lineage-specific differences being largely due to diversification and rapid turnover in gene families involved in environmental interactions. In contrast, about 20% of eutherian conserved non-coding elements (CNEs) are recent inventions that postdate the divergence of Eutheria and Metatheria. A substantial proportion of these eutherian-specific CNEs arose from sequence inserted by transposable elements, pointing to transposons as a major creative force in the evolution of mammalian gene regulation.

A mammal-specific Doublesex homolog associates with male sex chromatin and is required for male meiosis

Gametogenesis is a sexually dimorphic process requiring profound differences in germ cell differentiation between the sexes. In mammals, the presence of heteromorphic sex chromosomes in males creates additional sex-specific challenges, including incomplete X and Y pairing during meiotic prophase. This triggers formation of a heterochromatin domain, the XY body. The XY body disassembles after prophase, but specialized sex chromatin persists, with further modification, through meiosis. Here, we investigate the function of DMRT7, a mammal-specific protein related to the invertebrate sexual regulators Doublesex and MAB-3. We find that DMRT7 preferentially localizes to the XY body in the pachytene stage of meiotic prophase and is required for male meiosis. In Dmrt7 mutants, meiotic pairing and recombination appear normal, and a transcriptionally silenced XY body with appropriate chromatin marks is formed, but most germ cells undergo apoptosis during pachynema. A minority of mutant cells can progress to diplonema, but many of these escaping cells have abnormal sex chromatin lacking histone H3K9 di- and trimethylation and heterochromatin protein 1β accumulation, modifications that normally occur between pachynema and diplonema. Based on the localization of DMRT7 to the XY body and the sex chromatin defects observed in Dmrt7 mutants, we conclude that DMRT7 plays a role in the sex chromatin transformation that occurs between pachynema and diplonema. We suggest that DMRT7 may help control the transition from meiotic sex chromosome inactivation to postmeiotic sex chromatin in males. In addition, because it is found in all branches of mammals, but not in other vertebrates, Dmrt7 may shed light on evolution of meiosis and of sex chromatin.

Genes related to the sexual regulator Doublesex of Drosophila have been found to control sexual development in a wide variety of animals, ranging from roundworms to mammals. In this paper, we investigate the function of the Dmrt7 gene, one of seven related genes in the mouse. Female mammals are XX and males are XY, a chromosomal difference that presents specific challenges during the meiotic phase of male germ cell development. Some of these are thought to be overcome by incorporating the X and Y chromosomes into a specialized structure called the XY body. We find that DMRT7 protein is present in germ cells, localizes to the male XY body during meiosis, and is essential for male but not female fertility. The XY body normally is altered by recruitment of additional proteins and by specific modifications to histone proteins between the pachytene and diplotene stages of meiosis, but modification of the “sex chromatin” in Dmrt7 mutant cells is abnormal during this period. Because Dmrt7 is found in all branches of mammals, but not in other vertebrates, these results may indicate some commonality in regulation of sex chromatin among the mammals.

The search for a marsupial XIC reveals a break with vertebrate synteny

X-chromosome inactivation (XCI) evolved in mammals to deal with X-chromosome dosage imbalance between the XX female and the XY male. In eutherian mammals, random XCI of the soma requires a master regulatory locus known as the 'X-inactivation center' (XIC/Xic), wherein lies the noncoding XIST/Xist silencer RNA and its regulatory antisense Tsix gene. By contrast, marsupial XCI is imprinted to occur on the paternal X chromosome. To determine whether marsupials and eutherians share the XIC-driven mechanism, we search for the sequence equivalents in the genome of the South American opossum, Monodelphis domestica. Positional cloning and bioinformatic analysis reveal several interesting findings. First, protein-coding genes that flank the eutherian XIC are well-conserved in M. domestica, as well as in chicken, frog, and pufferfish. However, in M. domestica we fail to identify any recognizable XIST or TSIX equivalents. Moreover, cytogenetic mapping shows a surprising break in synteny with eutherian mammals and other vertebrates. Therefore, during the evolution of the marsupial X chromosome, one or more rearrangements broke up an otherwise evolutionarily conserved block of vertebrate genes. The failure to find XIST/TSIX in M. domestica may suggest that the ancestral XIC is too divergent to allow for detection by current methods. Alternatively, the XIC may have arisen relatively late in mammalian evolution, possibly in eutherians with the emergence of random XCI. The latter argues that marsupial XCI does not require XIST and opens the search for alternative mechanisms of dosage compensation.

The DXPas34 repeat regulates random and imprinted X inactivation

X chromosome inactivation (XCI) is initiated by expression of the noncoding Xist RNA in the female embryo. Tsix, the antisense noncoding partner of Xist, serves as its regulator during both imprinted and random XCI. Here, we show that Tsix in part acts through a 34mer repeat, DXPas34. DXPas34 contains bidirectional promoter activity, producing overlapping forward and reverse transcripts. We generate three new Tsix alleles in mouse embryonic stem cells and show that, while the Tsix promoter is unexpectedly dispensable, DXPas34 plays dual positive-negative functions. At the onset of XCI, DXPas34 stimulates Tsix expression through its enhancer activity. Once XCI is established, DXPas34 becomes repressive and stably silences Tsix. Germline transmission of the DXPas34 mutation demonstrates its necessity for both random and imprinted XCI in mice. Intriguingly, sequence analysis suggests that DXPas34 could potentially have descended from an ancient retrotransposon. We hypothesize that DXPas34 was acquired by Tsix to regulate antisense function.

Identification of a Ctcf cofactor, Yy1, for the X chromosome binary switch

In mammals, inactivation of one X chromosome in the female equalizes gene dosages between XX females and XY males. Two noncoding loci, Tsix and Xite, together regulate X chromosome fate by controlling homologous chromosome pairing, counting, and mutually exclusive choice. Following choice, the asymmetry of Xite and Tsix expression drives divergent chromosome fates, but how this pattern becomes established is currently unknown. Although no proven trans-acting factors have been identified, a likely candidate is Ctcf, a chromatin insulator with essential function in autosomal imprinting. Here, we search for trans-factors and identify Yy1 as a required cofactor for Ctcf. Paired Ctcf-Yy1 elements are highly clustered within the counting/choice and imprinting domain of Tsix. A deficiency of Yy1 leads to aberrant Tsix and Xist expression, resulting in a deficit of male and female embryos. Yy1 and Ctcf associate through specific protein-protein interactions and together transactivate Tsix. We propose that the Ctcf-Yy1-Tsix complex functions as a key component of the X chromosome binary switch.

Ki67 expression levels are a better marker of reduced melanoma growth following MEK inhibitor treatment than phospho-ERK levels

The loss of tumour phospho-extracellular responsive kinase (pERK) positivity is the major treatment biomarker for mitogen-activated protein kinase/extracellular responsive kinase (MEK) inhibitors. Here, we demonstrate that there is a poor correlation between pERK inhibition and the anti-proliferative effects of MEK inhibitors in melanoma cells. We suggest that Ki67 is a better biomarker for future clinical studies.

Epigenetic dynamics of the Kcnq1 imprinted domain in the early embryo

The mouse Kcnq1 imprinted domain is located on distal chromosome 7 and contains several imprinted genes that are paternally repressed. Repression of these genes is regulated by a non-coding antisense transcript, Kcnq1ot1, which is paternally expressed. Maternal repression of Kcnq1ot1 is controlled by DNA methylation originating in the oocyte. Some genes in the region are imprinted only in the placenta, whereas others are imprinted in both extra-embryonic and embryonic lineages. Here, we show that Kcnq1ot1 is paternally expressed in preimplantation embryos from the two-cell stage, and that ubiquitously imprinted genes proximal to Kcnq1ot1 are already repressed in blastocysts, ES cells and TS cells. Repressive histone marks such as H3K27me3 are present on the paternal allele of these genes in both ES and TS cells. Placentally imprinted genes that are distal to Kcnq1ot1, by contrast, are not imprinted in blastocysts, ES or TS cells. In these genes, paternal silencing and differential histone marks arise during differentiation of the trophoblast lineage between E4.5 and E7.5. Our findings show that the dynamics during preimplantation development of gene inactivation and acquisition of repressive histone marks in ubiquitously imprinted genes of the Kcnq1 domain are very similar to those of imprinted X inactivation. By contrast, genes that are only imprinted in the placenta, while regulated by the same non-coding RNA transcript Kcnq1ot1, undergo epigenetic inactivation during differentiation of the trophoblast lineage. Our findings establish a model for how epigenetic gene silencing by non-coding RNA may depend on distance from the non-coding RNA and on lineage and differentiation specific factors.

Postmeiotic sex chromatin in the male germline of mice

In mammals, the X and Y chromosomes are subject to meiotic sex chromosome inactivation (MSCI) during prophase I in the male germline, but their status thereafter is currently unclear. An abundance of X-linked spermatogenesis genes has spawned the view that the X must be active . On the other hand, the idea that the imprinted paternal X of the early embryo may be preinactivated by MSCI suggests that silencing may persist longer . To clarify this issue, we establish a comprehensive X-expression profile during mouse spermatogenesis. Here, we discover that the X and Y occupy a novel compartment in the postmeiotic spermatid and adopt a non-Rabl configuration. We demonstrate that this postmeiotic sex chromatin (PMSC) persists throughout spermiogenesis into mature sperm and exhibits epigenetic similarity to the XY body. In the spermatid, 87% of X-linked genes remain suppressed postmeiotically, while autosomes are largely active. We conclude that chromosome-wide X silencing continues from meiosis to the end of spermiogenesis, and we discuss implications for proposed mechanisms of imprinted X-inactivation.

Mapping of DNA replication origins to noncoding genes of the X-inactivation center

In mammals, few DNA replication origins have been identified. Although there appears to be an association between origins and epigenetic regulation, their underlying link to monoallelic gene expression remains unclear. Here, we identify novel origins of DNA replication (ORIs) within the X-inactivation center (Xic). We analyze 86 kb of the Xic using an unbiased approach and find an unexpectedly large number of functional ORIs. Although there has been a tight correlation between ORIs and CpG islands, we find that ORIs are not restricted to CpG islands and there is no dependence on transcriptional activity. Interestingly, these ORIs colocalize to important genetic elements or genes involved in X-chromosome inactivation. One prominent ORI maps to the imprinting center and to a domain within Tsix known to be required for X-chromosome counting and choice. Location and/or activity of ORIs appear to be modulated by removal of specific Xic elements. These data provide a foundation for testing potential relationships between DNA replication and epigenetic regulation in future studies.

A transient heterochromatic state in Xist preempts X inactivation choice without RNA stabilization

X chromosome inactivation (XCI) depends on a noncoding sense-antisense transcript pair, Xist and Tsix. At the onset of XCI, Xist RNA accumulates on one of two Xs, coating and silencing the chromosome in cis. The molecular basis for monoallelic Xist upregulation is not known, though evidence predominantly supports a posttranscriptional mechanism through RNA stabilization. Here, we test whether Tsix RNA destabilizes Xist RNA. Unexpectedly, we find that Xist upregulation is not based on transcript stabilization at all but is instead controlled by transcription in a sex-specific manner. Tsix directly regulates its transcription. On the future inactive X, Tsix downregulation induces a transient heterochromatic state in Xist, followed paradoxically by high-level Xist expression. A Tsix-deficient X chromosome adopts the heterochromatic state in pre-XCI cells. This state persists through XCI establishment and "reverts" to a euchromatic state during XCI maintenance. We have therefore identified chromatin marks that preempt and predict asymmetric Xist expression.

Differential methylation of Xite and CTCF sites in Tsix mirrors the pattern of X-inactivation choice in mice

During mammalian dosage compensation, one of two X-chromosomes in female cells is inactivated. The choice of which X is silenced can be imprinted or stochastic. Although genetic loci influencing the choice decision have been identified, the primary marks for imprinting and random selection remain undefined. Here, we examined the role of DNA methylation, a mechanism known to regulate imprinting in autosomal loci, and sought to determine whether differential methylation on the two Xs might predict their fates. To identify differentially methylated domains (DMDs) at the X-inactivation center, we used bisulfite sequencing and methylation-sensitive restriction enzyme analyses. We found DMDs in Tsix and Xite, two genes previously shown to influence choice. Interestingly, the DMDs in Tsix lie within CTCF binding sites. Allelic methylation differences occur in gametes and are erased in embryonic stem cells carrying two active Xs. Because the pattern of DNA methylation mirrors events of X-inactivation, we propose that differential methylation of DMDs in Tsix and Xite constitute a primary mark for epigenetic regulation. The discovery of DMDs in CTCF sites draws further parallels between X-inactivation and autosomal imprinting.

Transient homologous chromosome pairing marks the onset of X inactivation

Mammalian X inactivation turns off one female X chromosome to enact dosage compensation between XX and XY individuals. X inactivation is known to be regulated in cis by Xite, Tsix, and Xist, but in principle the two Xs must also be regulated in trans to ensure mutually exclusive silencing. Here, we demonstrate that interchromosomal pairing mediates this communication. Pairing occurs transiently at the onset of X inactivation and is specific to the X-inactivation center. Deleting Xite and Tsix perturbs pairing and counting/choice, whereas their autosomal insertion induces de novo X-autosome pairing. Ectopic X-autosome interactions inhibit endogenous X-X pairing and block the initiation of X-chromosome inactivation. Thus, Tsix and Xite function both in cis and in trans. We propose that Tsix and Xite regulate counting and mutually exclusive choice through X-X pairing.

The role of cardiopulmonary fitness and its genetic influences on surgical outcomes

Background

Outcome after major surgery remains poor in some patients. There is an increasing need to identify this cohort and develop strategies to reduce postsurgical morbidity and mortality. Central to outcome is the ability to mount cardiovascular output in response to the increased oxygen demand associated with major surgery.

Methods

A medline search was performed using keywords to identify factors that affect, and genetic influences in, disease and outcome from surgery, and all relevant English language articles published between 1980 and 2005 were retrieved. Secondary references were obtained from key articles.

Results

Preoperative cardiopulmonary exercise testing assesses patient fitness, highlights those at particular risk and, combined with triage to critical care, facilitates significant improvement in surgical outcome. However, genetic factors also influence responses to increased oxygen demand, and some patients are genetically predisposed to mounting increased inflammatory responses, which raise oxygen demand further. Polymorphisms in genes influencing fitness (angiotensin converting enzyme) and immune and inflammatory responses (such as interleukin 6) may associate with surgical outcome.

Conclusions

Development of preoperative screening methods like cardiopulmonary exercise testing and genotype analysis to identify index factors may permit better patient stratification, provide targets for future tailored treatments and so improve surgical outcome.