Association between chronic fatigue syndrome and the corticosteroid-binding globulin gene ALA SER224 polymorphism

Identification of a novel immune-related transcriptional regulatory network in sarcopenia

BACKGROUND

Sarcopenia is highly prevalent in elderly individuals and has a significant adverse effect on their physical health and quality of life, but the mechanisms remain unclear. Studies have indicated that transcription factors (TFs) and the immune microenvironment play a vital role in skeletal muscle atrophy.

METHODS

RNA-seq data of 40 muscle samples were downloaded from the GEO database. Then, differentially expressed genes (DEGs), TFs(DETFs), pathways(DEPs), and the expression of immune gene sets were identified with limma, edgeR, GO, KEGG, ORA, GSVA, and ssGSEA. Furthermore, the results above were integrated into coexpression analysis by Pearson correlation analysis (PCA). Significant coexpression patterns were used to construct the immune-related transcriptional regulatory network by Cytoscape and potential medicine targeting the network was screened by Connectivity Map. Finally, the regulatory mechanisms and RNA expression of DEGs and DETFs were identified by multiple online databases and RT‒qPCR.

RESULTS

We screened 808 DEGs (log2 fold change (FC) > 1 or <  - 1, p < 0.05), 4 DETFs (log2FC > 0.7 or <  - 0.7, p < 0.05), 304 DEPs (enrichment scores (ES) > 1 or <  - 1, p < 0.05), and 1208 differentially expressed immune genes sets (DEIGSs) (p < 0.01). Based on the results of PCA (correlation coefficient (CC) > 0.4 or <  - 0.4, p < 0.01), we then structured an immune-related network with 4 DETFs, 9 final DEGs, 11 final DEPs, and 6 final DEIGSs. Combining the results of online databases and in vitro experiments, we found that PAX5-SERPINA5-PI3K/Akt (CC ≤ 0.444, p ≤ 0.004) was a potential transcriptional regulation axis, and B cells (R = 0.437, p = 0.005) may play a vital role in this signal transduction. Finally, the compound of trichostatin A (enrichment = -0.365, specificity = 0.4257, p < 0.0001) might be a potential medicine for sarcopenia based on the PubChem database and the result of the literature review.

CONCLUSIONS

We first identified immune-related transcriptional regulatory network with high-throughput RNA-seq data in sarcopenia. We hypothesized that PAX5-SERPIAN5-PI3K/Akt axis is a potential mechanism in sarcopenia and that B cells may play a vital role in this signal transduction. In addition, trichostatin A might be a potential medicine for sarcopenia.

Serine protease inhibitors and human wellbeing interplay: new insights for old friends

Serine Protease Inhibitors (Serpins) control tightly regulated physiological processes and their dysfunction is associated to various diseases. Thus, increasing interest is given to these proteins as new therapeutic targets. Several studies provided functional and structural data about human serpins. By comparison, only little knowledge regarding bacterial serpins exists. Through the emergence of metagenomic studies, many bacterial serpins were identified from numerous ecological niches including the human gut microbiota. The origin, distribution and function of these proteins remain to be established. In this report, we shed light on the key role of human and bacterial serpins in health and disease. Moreover, we analyze their function, phylogeny and ecological distribution. This review highlights the potential use of bacterial serpins to set out new therapeutic approaches.

Polygenic risk score of SERPINA6/SERPINA1 associates with diurnal and stress-induced HPA axis activity in children

PURPOSE

Corticosteroid-binding globulin (CBG) transports glucocorticoids in blood. Variation in genes SERPINA6 encoding for CBG, SERPINA2 and SERPINA1 (serpin family A member 6, 2, and 1) have been shown to influence morning plasma cortisol and CBG in adults. However, association of this genetic variation with diurnal and stress-induced salivary cortisol remain unknown. This study aims to investigate the effect of genetic variation in SERPINA6/2/1 loci on diurnal and stress-induced salivary cortisol in children.

METHODS

We studied 186, 8-year-old children with genome-wide genotyping. We generated weighted polygenic risk score (PRS) based on 6 genome-wide significant SNPs (rs11621961, rs11629171, rs7161521, rs2749527, rs3762132, rs4900229) derived from the CORNET meta-analyses. Salivary cortisol was measured across one day and in response to the Trier Social Stress Test for Children (TSST-C).

RESULTS

Mixed models, adjusted for covariates, showed that the PRS x sampling time interactions associated with diurnal (P < 0.001) and stress-induced (P = 0.009) salivary cortisol. In the high PRS group (dichotomized at median) the diurnal salivary cortisol pattern decreased less from awakening to bedtime than in the low PRS group (standardized estimates of sampling time -0.64 vs. -0.73, P < 0.0001 for both estimates). In response to stress, salivary cortisol increased in the high PRS group while it remained unchanged in the low PRS group (standardized estimates of sampling time 0.12, P = 0.015 vs. -0.06, P = 0.16). These results were mainly driven by minor alleles of rs7161521 (SERPINA6) and rs4900229 (SERPINA1).

CONCLUSIONS

Genetic variation in SERPINA6/2/1loci may underpin higher hypothalamic-pituitary-adrenocortical axis activity in children.

Corticosteroid-binding globulin: acute and chronic inflammation

Corticosteroid-binding globulin (CBG) is the principal transport protein for cortisol binding 80% in a 1:1 ratio. Since its discovery in 1958, CBG's primary function has been considered to be cortisol transport within the circulation. More recent data indicate a cortisol tissue delivery function, particularly at inflammatory sites. CBG's structure as a non-inhibitory serine protease inhibitor allows allosteric structural change after reactive central loop (RCL) cleavage by neutrophil elastase (NE) and RCL insertion into CBG's protein core. Transition from the high to low affinity CBG form reduces cortisol-binding. Areas covered: In acute systemic inflammation, high affinity CBG (haCBG) is depleted proportionate to sepsis severity, with lowest levels seen in non-survivors. Conversely, in chronic inflammation, CBG cleavage is paradoxically reduced in proportion to disease severity, implying impaired targeted delivery of cortisol. CBG's structure allows thermosensitive release of bound cortisol, by reversible partial insertion of the RCL and loosening of CBG:cortisol binding. Recent studies indicate a significant frequency of function-altering single nucleotide polymorphisms of the SERPINA6 gene which may be important in population risk of inflammatory disease. Expert commentary: Further exploration of CBG in inflammatory disease may offer new avenues for treatment based on the model of optimal cortisol tissue delivery.

Pathway-focused genetic evaluation of immune and inflammation related genes with chronic fatigue syndrome

Recent evidence suggests immune and inflammatory alterations are important in chronic fatigue syndrome (CFS). This study was done to explore the association of functionally important genetic variants in inflammation and immune pathways with CFS. Peripheral blood DNA was isolated from 50 CFS and 121 non-fatigued (NF) control participants in a population-based study. Genotyping was performed with the Affymetrix Immune and Inflammation Chip that covers 11K single nucleotide polymorphisms (SNPs) following the manufacturer's protocol. Genotyping accuracy for specific genes was validated by pyrosequencing. Golden Helix SVS software was used for genetic analysis. SNP functional annotation was done using SPOT and GenomePipe programs. CFS was associated with 32 functionally important SNPs: 11 missense variants, 4 synonymous variants, 11 untranslated regulatory region (UTR) variants and 6 intronic variants. Some of these SNPs were in genes within pathways related to complement cascade (SERPINA5, CFB, CFH, MASP1 and C6), chemokines (CXCL16, CCR4, CCL27), cytokine signaling (IL18, IL17B, IL2RB), and toll-like receptor signaling (TIRAP, IRAK4). Of particular interest is association of CFS with two missense variants in genes of complement activation, rs4151667 (L9H) in CFB and rs1061170 (Y402H) in CFH. A 5' UTR polymorphism (rs11214105) in IL18 also associated with physical fatigue, body pain and score for CFS case defining symptoms. This study identified new associations of CFS with genetic variants in pathways including complement activation providing additional support for altered innate immune response in CFS. Additional studies are needed to validate the findings of this exploratory study.

Metabolism in chronic fatigue syndrome

Chronic fatigue syndrome (CFS) is a poorly understood condition that presents as long-term physical and mental fatigue with associated symptoms of pain and sensitivity across a broad range of systems in the body. The poor understanding of the disorder comes from the varying clinical diagnostic definitions as well as the broad array of body systems from which its symptoms present. Studies on metabolism and CFS suggest irregularities in energy metabolism, amino acid metabolism, nucleotide metabolism, nitrogen metabolism, hormone metabolism, and oxidative stress metabolism. The overwhelming body of evidence suggests an oxidative environment with the minimal utilization of mitochondria for efficient energy production. This is coupled with a reduced excretion of amino acids and nitrogen in general. Metabolomics is a developing field that studies metabolism within a living system under varying conditions of stimuli. Through its development, there has been the optimisation of techniques to do large-scale hypothesis-generating untargeted studies as well as hypothesis-testing targeted studies. These techniques are introduced and show an important future direction for research into complex illnesses such as CFS.

Update of the human and mouse SERPIN gene superfamily

The serpin family comprises a structurally similar, yet functionally diverse, set of proteins. Named originally for their function as serine proteinase inhibitors, many of its members are not inhibitors but rather chaperones, involved in storage, transport, and other roles. Serpins are found in genomes of all kingdoms, with 36 human protein-coding genes and five pseudogenes. The mouse has 60 Serpin functional genes, many of which are orthologous to human SERPIN genes and some of which have expanded into multiple paralogous genes. Serpins are found in tissues throughout the body; whereas most are extracellular, there is a class of intracellular serpins. Serpins appear to have roles in inflammation, immune function, tumorigenesis, blood clotting, dementia, and cancer metastasis. Further characterization of these proteins will likely reveal potential biomarkers and therapeutic targets for disease.

Two different corticosteroid-binding globulin variants that lack cortisol-binding activity in a greek woman

BACKGROUND

Corticosteroid-binding globulin (CBG), encoded by SERPINA6, is the principal plasma binding protein for cortisol. Most nonsynonymous single-nucleotide polymorphisms that alter the production or function of CBG occur rarely, and their clinical significance remains obscure.

METHODS

Serum and DNA were obtained from a Greek woman with low morning cortisol levels and from family members. SERPINA6 exons were sequenced, and serum CBG was measured by ELISA and cortisol-binding capacity assay. Recombinant CBG variants were produced for detailed functional studies.

RESULTS

A novel heterozygous c.1282G>C transversion in exon 5 of SERPINA6, resulting in a p.Trp393Ser (W371S) substitution, was identified in the proband, who was also heterozygous for single-nucleotide polymorphisms encoding the CBG Lyon (D367N) and CBG A224S variants. The proband had no measurable plasma cortisol-binding activity despite a CBG level of 273 nm by ELISA. She inherited CBG W371S from her mother whose plasma cortisol-binding capacity was approximately 50% lower than the CBG measurements by ELISA (314 nm). The proband's father and four children were heterozygous for CBG D367N; their CBG levels by ELISA were normal, but corresponding cortisol-binding capacity measurements were 50% lower. Pedigree analysis revealed that W371S segregates with A224 and that D367N and W371S segregate separately. Recombinant CBG D367N and CBG W371S had no measureable cortisol-binding activity.

CONCLUSION

A new CBG Athens (W371S) variant that lacks cortisol-binding activity has been identified in a carrier of the cortisol-binding deficient CBG Lyon (D367N) variant. Analyses of CBG levels in this pedigree illustrate how immunoassays fail to accurately reflect cortisol-binding activity.

A role for corticosteroid-binding globulin variants in stress-related disorders

Primary stress-related diseases such as chronic fatigue syndrome, fibromyalgia or chronic widespread pain have been associated with altered activity of the hypothalamic-pituitary-adrenal axis due to measured relative hyper- or hypo-cortisolism in basal or experimentally stimulated states. A hereditary risk to development of these diseases has been proposed. Corticosteroid-binding globulin (CBG), a plasma transport vehicle for cortisol, may play a more active role in the hypothalamic-pituitary-adrenal axis. Chronically altered hypothalamic-pituitary-adrenal axis has been associated with common medical problems. Hypocortisolism has been observed in kindred studies of rare mutations of the SERPIN A6 (CBG) gene and more common SERPIN A6 polymorphisms associated with reduced CBG levels or CBG:cortisol-binding affinity. Over the last decade, studies of five different CBG gene mutations in humans, human genetic associations and transgenic mouse models have suggested that CBG may have hitherto unexpected roles in modulation of the stress response. Naturally occurring CBG variants may alter susceptibility to disorders associated with chronic stress and relative hypocortisolism. On the other hand, hypercortisolism has been linked with Cushing's disease and metabolic syndrome and CBG gene polymorphisms have been linked to obesity in animal models. In this article, we look at the evidence suggesting a role for CBG in stress-related disorders, focusing particularly on CBG gene polymorphisms and chronic pain/fatigue syndromes.

CBG Santiago: a novel CBG mutation

CONTEXT

Corticosteroid-binding globulin (CBG; SERPIN A6) gene mutations are rare; only four mutations have been described, often in association with fatigue and chronic pain, albeit with incomplete penetrance.

PATIENT

We report a kindred with a novel SERPINA6 mutation. The proband, a 9-yr-old male, had excessive postexertional fatigue, weakness, and migraine.

MAIN OUTCOME MEASURES AND RESULTS

Investigations revealed low morning and ACTH-stimulated peak cortisol levels. SERPIN A6 sequencing detected a novel exon 2 single base deletion (c.13delC) leading to a frameshift generating a stop codon within the signal peptide coding region (p.Leu5CysfsX26) and 50% reduced CBG levels in heterozygotes. The patient's father and two sisters share the mutation. Symptom expression within the family may have been modified by a polymorphic CBG allele (c.735G>T). Exogenous hydrocortisone had no effect on the fatigue.

CONCLUSION

This report documents the fifth CBG gene mutation in humans and the second causing major effects on CBG levels. Individuals with low CBG levels may be misdiagnosed as having secondary hypocortisolism. The association with fatigue and idiopathic pain is again noted and may relate to altered stress system function. Variability of the phenotype may relate to other genetic variations of the CBG gene or environmental factors.

Clinical manifestations of highly prevalent corticosteroid-binding globulin mutations in a village in southern Italy

CONTEXT

Corticosteroid-binding globulin (CBG) is the binding protein for cortisol. Rare kindreds with CBG mutations reducing CBG levels or altering binding affinity have been described, along with clinical manifestations encompassing fatigue, chronic pain, and hypotension. The largest kindred, exhibiting two mutations (null and Lyon) were Australian immigrants from Italy.

OBJECTIVE

Our objective was to determine the prevalence of the null/Lyon mutations in the village where the original null/Lyon family emigrated and compare subjects with and without CBG mutations, without previous knowledge of their mutation status.

DESIGN, SETTING, AND PARTICIPANTS

We conducted a survey field study that included 495 adult residents.

MAIN OUTCOMES

We assessed clinical history, CBG mutation analysis, plasma CBG, salivary cortisol, body mass index, waist circumference, blood pressure, and the Krupp fatigue scale.

RESULTS

Eighteen of 495 participants (3.6%, seven males and 11 females) had one of two function-altering CBG mutations. All were heterozygous for the null (n = 6) or Lyon mutations (n = 12). Of 12 Lyon participants (four males and eight females), eight (two males and six females) had chronic widespread pain and five osteoarthritis with associated pain (one male and four females). Of six null participants (three males and three females), three (one male and two females) had chronic pain and four osteoarthritis with associated pain (two males and two females).

CONCLUSIONS

A high combined prevalence (3.6%) of these two CBG mutations was detected. The presence of either mutation conferred a propensity to chronic pain. In other communities, individuals with the same genetic background complain more of fatigue than pain, suggesting an environmental effect on the phenotype. These findings, combined with animal CBG gene knockout and human CBG single-nucleotide polymorphism haplotype studies, suggest that CBG influences the endocrine and neurobehavioral response to stress, including the development of pain/fatigue syndromes.

Molecular and structural basis of steroid hormone binding and release from corticosteroid-binding globulin

Corticosteroid-binding globulin (CBG), a non-inhibitory member of the serine proteinase inhibitor (serpin) super-family, is the high-affinity transport protein for glucocorticoids in vertebrate blood. Plasma CBG is a glycoprotein with 30% of its mass represented by N-linked oligosaccharide chains. Its well-characterized steroid-binding properties represent a "bench-mark data set" used extensively for in silico studies of protein-ligand interactions and drug design. Recent crystal structure analyses of intact rat CBG and cleaved human CBG have revealed the precise topography of the steroid-binding site, and shown that cortisol-bound CBG displays a typical stressed (S) serpin conformation with the reactive center loop (RCL) fully exposed from the central beta-sheet A, while proteolytic cleavage of the RCL results in CBG adopting a relaxed (R) conformation with the cleaved RCL fully inserted within the protein core. These crystal structures have set the stage for mechanistic studies of CBG function which have so far shown that helix D plays a key role in coupling RCL movement and steroid-binding site integrity, and provided evidence for an allosteric mechanism that modulates steroid binding and release from CBG. These studies have also revealed how the irreversible release of steroids occurs after proteolysis and re-orientation of the RCL within the R conformation. This recent insight into the structure and function of CBG reveals how naturally occurring genetic CBG mutations affect steroid binding, and helps understand how proteolysis of CBG enhances the targeted delivery of biologically active steroids to their sites of action.

Corticosteroid-binding globulin: the clinical significance of altered levels and heritable mutations

Corticosteroid-binding globulin (CBG) is the specific high-affinity plasma transport glycoprotein for cortisol. Stress-induced falls in CBG levels may heighten hypothalamic-pituitary-adrenal axis responses and CBG:tissue interactions may allow targeted cortisol delivery. Three genetic variants of CBG have been identified that reduce cortisol binding affinity and/or CBG levels. These include the Leuven and Lyon mutations which reduce CBG:cortisol binding affinity 3- and 4-fold, respectively, and the null mutation resulting in a 50% (heterozygote) or 100% (homozygote) reduction in CBG levels. The three reported null homozygotes demonstrate that complete CBG deficiency is not lethal, although it may be associated with hypotension and fatigue. The phenotype of a CBG null murine model included fatigue and immune defects. One community-based study revealed that severe CBG mutations are rare in idiopathic fatigue disorders. The mechanisms by which CBG mutations may cause fatigue are unknown. There are preliminary data of altered CBG levels in hypertension and in the metabolic syndrome; however, the nature of these associations is uncertain. Further studies may clarify the functions of CBG, and clinical observations may validate and/or extend the phenotypic features of various CBG mutations.

Genetic evaluation of the serotonergic system in chronic fatigue syndrome

Chronic fatigue syndrome (CFS) is a debilitating disorder of unknown etiology with no known lesions, diagnostic markers or therapeutic intervention. The pathophysiology of CFS remains elusive, although abnormalities in the central nervous system (CNS) have been implicated, particularly hyperactivity of the serotonergic (5-hydroxytryptamine; 5-HT) system and hypoactivity of the hypothalamic-pituitary-adrenal (HPA) axis. Since alterations in 5-HT signaling can lead to physiologic and behavioral changes, a genetic evaluation of the 5-HT system was undertaken to identify serotonergic markers associated with CFS and potential mechanisms for CNS abnormality. A total of 77 polymorphisms in genes related to serotonin synthesis (TPH2), signaling (HTR1A, HTR1E, HTR2A, HTR2B, HTR2C, HTR3A, HTR3B, HTR4, HTR5A, HTR6, and HTR7), transport (SLC6A4), and catabolism (MAOA) were examined in 137 clinically evaluated subjects (40 CFS, 55 with insufficient fatigue, and 42 non-fatigued, NF, controls) derived from a population-based CFS surveillance study in Wichita, Kansas. Of the polymorphisms examined, three markers (-1438G/A, C102T, and rs1923884) all located in the 5-HT receptor subtype HTR2A were associated with CFS when compared to NF controls. Additionally, consistent associations were observed between HTR2A variants and quantitative measures of disability and fatigue in all subjects. The most compelling of these associations was with the A allele of -1438G/A (rs6311) which is suggested to have increased promoter activity in functional studies. Further, in silico analysis revealed that the -1438 A allele creates a consensus binding site for Th1/E47, a transcription factor implicated in the development of the nervous system. Electrophoretic mobility shift assay supports allele-specific binding of E47 to the A allele but not the G allele at this locus. These data indicate that sequence variation in HTR2A, potentially resulting in its enhanced activity, may be involved in the pathophysiology of CFS.

Is chronic fatigue syndrome (CFS/ME) heritable in children, and if so, why does it matter?

We need a clear definition of CFS/ME in children and sample sizes for genetic studies need to be much larger

Corticosteroid-binding globulin gene polymorphisms: clinical implications and links to idiopathic chronic fatigue disorders

Corticosteroid-binding globulin (CBG) binds cortisol with high affinity, facilitating transport of cortisol in blood, although tissue-specific CBG-cortisol interactions have long been postulated. There are three heritable, human CBG gene mutations that can reduce CBG-cortisol binding affinity and/or reduce circulating CBG levels. In some families, fatigue and low blood pressure have been associated with affinity altering or CBG level reducing mutations. The limited numbers of reports raise the possibility of ascertainment bias as many cases presented with features suggesting cortisol deficiency. The recent description of a genetically CBG-deficient mouse listed fatigue, manifest as reduced activity levels, as part of the phenotype, which also included immune aberrations. Severe CBG mutations may produce fatigue, but one study suggests that these are a rare cause of idiopathic fatigue. A mechanism for the effect of CBG mutations on fatigue is not readily apparent because free cortisol levels are normal, although we speculate that CBG may have an effect on cortisol-brain transport.

Glucocorticoid receptor polymorphisms and haplotypes associated with chronic fatigue syndrome

Chronic fatigue syndrome (CFS) is a significant public health problem of unknown etiology, the pathophysiology has not been elucidated, and there are no characteristic physical signs or laboratory abnormalities. Some studies have indicated an association of CFS with deregulation of immune functions and hypothalamic-pituitary-adrenal (HPA) axis activity. In this study, we examined the association of sequence variations in the glucocorticoid receptor gene (NR3C1) with CFS because NR3C1 is a major effector of the HPA axis. There were 137 study participants (40 with CFS, 55 with insufficient symptoms or fatigue, termed as ISF, and 42 non-fatigued controls) who were clinically evaluated and identified from the general population of Wichita, KS. Nine single nucleotide polymorphisms (SNPs) in NR3C1 were tested for association of polymorphisms and haplotypes with CFS. We observed an association of multiple SNPs with chronic fatigue compared to non-fatigued (NF) subjects (P < 0.05) and found similar associations with quantitative assessments of functional impairment (by the SF-36), with fatigue (by the Multidimensional Fatigue Inventory) and with symptoms (assessed by the Centers for Disease Control Symptom Inventory). Subjects homozygous for the major allele of all associated SNPs were at increased risk for CFS with odds ratios ranging from 2.61 (CI 1.05-6.45) to 3.00 (CI 1.12-8.05). Five SNPs, covering a region of approximately 80 kb, demonstrated high linkage disequilibrium (LD) in CFS, but LD gradually declined in ISF to NF subjects. Furthermore, haplotype analysis of the region in LD identified two associated haplotypes with opposite alleles: one protective and the other conferring risk of CFS. These results demonstrate NR3C1 as a potential mediator of chronic fatigue, and implicate variations in the 5' region of NR3C1 as a possible mechanism through which the alterations in HPA axis regulation and behavioural characteristics of CFS may manifest.

Mirrored symptoms in mother and child with chronic fatigue syndrome

OBJECTIVE

Our aim with this study was to assess the relation between chronic fatigue syndrome in adolescents and fatigue and associated symptoms in their fathers and mothers, more specifically the presence of chronic fatigue syndrome-like symptoms and psychologic distress.

METHOD

In this cross-sectional study, 40 adolescents with chronic fatigue syndrome according to the Centers for Disease Control and Prevention criteria were compared with 36 healthy control subjects and their respective parents. Questionnaires regarding fatigue (Checklist Individual Strength), fatigue-associated symptoms, and psychopathology (Symptom Checklist-90) were applied to the children and their parents.

RESULTS

Psychologic distress in the mother corresponds with an adjusted odds ratio of 5.6 for the presence of CFS in the child. The presence of fatigue in the mother and dimensional assessment of fatigue with the Checklist Individual Strength revealed odds ratios of, respectively, 5.29 and 2.86 for the presence of chronic fatigue syndrome in the child. An increase of 1 SD of the hours spent by the working mother outside the home reduced the risk for chronic fatigue syndrome in their child with 61%. The fathers did not show any risk indicator for chronic fatigue syndrome in their child.

CONCLUSIONS

Mothers of adolescents with chronic fatigue syndrome exhibit fatigue and psychologic symptoms similar to their child in contrast with the fathers. The striking difference between the absent association in fathers and the evident association in mothers suggests that the shared symptom complex of mother and child is the result of an interplay between genetic vulnerability and environmental factors.

An overview of the serpin superfamily

Serpins are a broadly distributed family of protease inhibitors that use a conformational change to inhibit target enzymes. They are central in controlling many important proteolytic cascades, including the mammalian coagulation pathways. Serpins are conformationally labile and many of the disease-linked mutations of serpins result in misfolding or in pathogenic, inactive polymers.

Chronic fatigue syndrome: the need for subtypes

Chronic fatigue syndrome (CFS) is an important condition confronting patients, clinicians, and researchers. This article provides information concerning the need for appropriate diagnosis of CFS subtypes. We first review findings suggesting that CFS is best conceptualized as a separate diagnostic entity rather than as part of a unitary model of functional somatic distress. Next, research involving the case definitions of CFS is reviewed. Findings suggest that whether a broad or more conservative case definition is employed, and whether clinic or community samples are recruited, these decisions will have a major influence in the types of patients selected. Review of further findings suggests that subtyping individuals with CFS on sociodemographic, functional disability, viral, immune, neuroendocrine, neurology, autonomic, and genetic biomarkers can provide clarification for researchers and clinicians who encounter CFS' characteristically confusing heterogeneous symptom profiles. Treatment studies that incorporate subtypes might be particularly helpful in better understanding the pathophysiology of CFS. This review suggests that there is a need for greater diagnostic clarity, and this might be accomplished by subgroups that integrate multiple variables including those in cognitive, emotional, and biological domains.