Multiple mechanisms of self-association of chemokine receptors CXCR4 and CCR5 demonstrated by deep mutagenesis.

Chemokine receptors are members of the rhodopsin-like class A GPCRs whose signaling through G proteins drives the directional movement of cells in response to a chemokine gradient. Chemokine receptors CXCR4 and CCR5 have been extensively studied due to their roles in leukocyte development and inflammation and their status as coreceptors for HIV-1 infection, among other roles. Both receptors form dimers or oligomers of unclear function. While CXCR4 has been crystallized in a dimeric arrangement, available atomic resolution structures of CCR5 are monomeric. To investigate their dimerization interfaces, we used a bimolecular fluorescence complementation (BiFC)-based screen and deep mutational scanning to find mutations that change how the receptors self-associate, either via specific oligomer assembly or alternative mechanisms of clustering in close proximity. Many disruptive mutations promoted self-associations nonspecifically, suggesting they aggregated in the membrane. A mutationally intolerant region was found on CXCR4 that matched the crystallographic dimer interface, supporting this dimeric arrangement in living cells. A mutationally intolerant region was also observed on the surface of CCR5 by transmembrane helices 3 and 4. Mutations predicted from the scan to reduce BiFC were validated and were localized in the transmembrane domains as well as the C-terminal cytoplasmic tails where they reduced lipid microdomain localization. A mutation in the dimer interface of CXCR4 had increased binding to the ligand CXCL12 and yet diminished calcium signaling. There was no change in syncytia formation with cells expressing HIV-1 Env. The data highlight that multiple mechanisms are involved in self-association of chemokine receptor chains.

Multiple mechanisms of self-association of chemokine receptors CXCR4 and CCR5 demonstrated by deep mutagenesis.

Chemokine receptors are members of the rhodopsin-like class A GPCRs whose signaling through G proteins drives the directional movement of cells in response to a chemokine gradient. Chemokine receptors CXCR4 and CCR5 have been extensively studied due to their roles in white blood cell development and inflammation and their status as coreceptors for HIV-1 infection, among other functions. Both receptors form dimers or oligomers but the function/s of self-associations are unclear. While CXCR4 has been crystallized in a dimeric arrangement, available atomic resolution structures of CCR5 are monomeric. To investigate the dimerization interfaces of these chemokine receptors, we used a bimolecular fluorescence complementation (BiFC)-based screen and deep mutational scanning to find mutations that modify receptor self-association. Many disruptive mutations promoted self-associations nonspecifically, suggesting they aggregated in the membrane. A mutationally intolerant region was found on CXCR4 that matched the crystallographic dimer interface, supporting this dimeric arrangement in living cells. A mutationally intolerant region was also observed on the surface of CCR5 by transmembrane helices 3 and 4. Mutations from the deep mutational scan that reduce BiFC were validated and were localized in the transmembrane domains as well as the C-terminal cytoplasmic tails where they reduced lipid microdomain localization. The reduced self-association mutants of CXCR4 had increased binding to the ligand CXCL12 but diminished calcium signaling. There was no change in syncytia formation with cells expressing HIV-1 Env. The data highlight that multiple mechanisms are involved in self-association of chemokine receptor chains.

MR Neurography of Lumbosacral Plexus: Incremental Value Over XR, CT, and MRI of L Spine With Improved Outcomes in Patients With Radiculopathy and Failed Back Surgery Syndrome.

BACKGROUND: Lower back pain is often evaluated using magnetic resonance imaging (MRI) and conventional imaging, which provide incomplete information about the etiology of pain and lead to less than optimal management. HYPOTHESIS: MR neurography (MRN) of the lumbosacral (LS) plexus renders a more accurate diagnosis, alters the management strategy, and clinical outcomes of radiculopathy or failed back surgery Syndrome (FBSS) patients when compared to the conventional imaging modalities. STUDY TYPE: Retrospective, cross-sectional. POPULATION: A total of 356 patients (mean age 65.8 ± 12.3; 48.9% female) from single university hospital over 6 years with MRN of LS plexus were included from a cohort of 14,775 total patients with lumbar spine MR imaging. ASSESSMENT: Conventional imaging obtained before and after MRN of LS plexus was reevaluated and categorized into three levels based on extent of imaging findings' correlation to presenting clinical symptoms (contributory levels). Clinical notes were reviewed for changes in ordering provider's recommended management and subsequent patients' symptom level pre-MRN to post-MRN. FIELD STRENGTH/SEQUENCE: A 5 T and 3.0 T. T1-weighted (T1W), T2-weighted (T2W), short T1 inversion recovery (STIR), T1 turbo spin echo (T1 TSE), T2 spectral attenuated inversion recovery (T2 SPAIR). STATISTICAL TESTS: Chi-squared test. Statistical significance was set at P < 0.05. RESULTS: A total of 356 total patients (174 females) with mean age ± SD was 65.8 ± 12.3 years, 4.2% of patients imaged with lumbar spine MRI. Definitely contributory studies among X-rays, computed tomography, MRI, and MRN were 3 of the 129 (2.3%), 3 of the 48 (6.2%), 35 of the 184 (19.0%), and 283 of the 356 (79.8%), respectively. Pre-MRN vs. post-MRN led to change in recommendation in 219 of the 356 (61.5%) patients and 71 of the 99 (71.7%) patients had improved symptoms. CONCLUSION: MRN of the LS plexus can provide more corroborative image findings for symptom correlation compared to other imaging modalities for accurate diagnosis, effects patient management and leads to positive clinical outcomes in a small subset of patients with radiculopathy or FBSS. EVIDENCE LEVEL: 4 TECHNICAL EFFICACY: Stage 5.

Clinical Outcomes of Coccygectomy for Coccydynia: A Single Institution Series With Mean 5-Year Follow-Up.

BACKGROUND: Prior studies of coccygectomy consist of small patient groups, heterogeneous techniques, and high wound complication rates (up to 22%). This study investigates our institution's experience with coccygectomy using a novel "off-center" wound closure technique and analyzes prognostic factors for long-term successful clinical outcomes. METHODS: Retrospective review of all patients who underwent coccygectomy from 2006 to 2019 at a single center. Demographics, mechanism of injury, conservative management, morphology (Postacchini and Massobrio), and postoperative complications were collected. Preoperative and postoperative Oswestry Disability Index (ODI), visual analog scale (VAS), Patient-Reported Outcomes Measurement Information System-29 (PROMIS-29), and EuroQol-5D (EQ-5D) were compared. Risk factors for failing to meet minimum clinically importance difference for ODI and PROMIS-physical function/pain interference were identified. Risk factors for remaining disabled after surgery (ODI <20) and factors associated with VAS and EQ-5D improvement were investigated using stepwise logistic regression. RESULTS: A total of 173 patients (77% women, mean age = 46.56 years, mean follow-up 5.58 ± 3.95 years). The most common etiologies of coccydynia were spontaneous/unknown (42.2%) and trauma/accident (41%). ODI, VAS, and several PROMIS-29 domains improved postoperatively. Older age predicted continued postoperative disability (ODI >20) and history of prior spine surgery, trauma etiology, and women had inferior outcomes. No history of spine surgery (cervical, thoracic, or lumbar) prior to coccygectomy was found to predict improved postoperative VAS back scores. No outcome differences were demonstrated among the coccyx morphologies. Sixteen patients (9.25%) were noted to have postoperative infections of the incision site with no difference in long-term outcomes (all P <0.05). CONCLUSIONS: This is the largest series of coccygectomy patients demonstrating improvement in long-term outcomes. Compared to previous studies, our cohort had a lower wound infection rate, which we attribute to an "off-center" closure. CLINICAL RELEVANCE: Patients should be counseled that their surgical history, along with age, gender, and etiology of pain can influence success following coccygectomy. These data can help surgeons set realistic expectations following surgery.

Coccygectomy for refractory coccygodynia: a systematic review and meta-analysis.

PURPOSE: We sought to systematically assess and summarize the available literature on outcomes following coccygectomy for refractory coccygodynia. METHODS: PubMed, Scopus, and Cochrane Library databases were systematically searched in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Data concerning patient demographics, validated patient reported outcome measures (PROMs) for pain relief, disability outcomes, complications, and reoperation rates were extracted and analyzed. RESULTS: A total of 21 studies (18 retrospective and 3 prospective) were included in the quantitative analysis. A total of 826 patients (females = 75%) received coccygectomy (720 total and 106 partial) for refractory coccygodynia. Trauma was reported as the most common etiology of coccygodynia (56%; n = 375), followed by idiopathic causes (33%; n = 221). The pooled mean difference (MD) in pain scores from baseline on a 0-10 scale was 5.03 (95% confidence interval [CI]: 4.35 to 6.86) at a 6-12 month follow-up (FU); 5.02 (95% CI: 3.47 to 6.57) at > 12-36 months FU; and 5.41 (95% CI: 4.33 to 6.48) at > 36 months FU. The MCID threshold for pain relief was surpassed at each follow-up. Oswestry Disability Index scores significantly improved postoperatively, with a pooled MD from baseline of - 23.49 (95% CI: - 31.51 to - 15.46), surpassing the MCID threshold. The pooled incidence of complications following coccygectomy was 8% (95% CI: 5% to 12%), the most frequent of which were surgical site infections and wound dehiscence. The pooled incidence of reoperations was 3% (95% CI: 1% to 5%). CONCLUSION: Coccygectomy represents a viable treatment option in patients with refractory coccygodynia.

Engineered receptors for human cytomegalovirus that are orthogonal to normal human biology.

A trimeric glycoprotein complex on the surface of human cytomegalovirus (HCMV) binds to platelet-derived growth factor (PDGF) receptor α (PDGFRα) to mediate host cell recognition and fusion of the viral and cellular membranes. Soluble PDGFRα potently neutralizes HCMV in tissue culture, and its potential use as an antiviral therapeutic has the benefit that any escape mutants will likely be attenuated. However, PDGFRα binds multiple PDGF ligands in the human body as part of developmental programs in embryogenesis and continuing through adulthood. Any therapies with soluble receptor therefore come with serious efficacy and safety concerns, especially for the treatment of congenital HCMV. Soluble virus receptors that are orthogonal to human biology might resolve these concerns. This engineering problem is solved by deep mutational scanning on the D2-D3 domains of PDGFRα to identify variants that maintain interactions with the HCMV glycoprotein trimer in the presence of competing PDGF ligands. Competition by PDGFs is conformation-dependent, whereas HCMV trimer binding is independent of proper D2-D3 conformation, and many mutations at the receptor-PDGF interface are suitable for functionally separating trimer from PDGF interactions. Purified soluble PDGFRα carrying a targeted mutation succeeded in displaying wild type affinity for HCMV trimer with a simultaneous loss of PDGF binding, and neutralizes trimer-only and trimer/pentamer-expressing HCMV strains infecting fibroblasts or epithelial cells. Overall, this work makes important progress in the realization of soluble HCMV receptors for clinical application.

MR neurography of the brachial plexus in adult and pediatric age groups: evolution, recent advances, and future directions.

Introduction: MR neurography (MRN) of the brachial plexus has emerged in recent years as a safe and accurate modality for the identification of brachial plexopathies in pediatric and adult populations. While clinical differentiation of brachial plexopathy from cervical spine-related radiculopathy or nerve injury has long relied upon nonspecific physical exam and electrodiagnostic testing modalities, MRN now permits detailed interrogation of peripheral nerve anatomy and pathology, as well as assessment of surrounding soft tissues and musculature, thereby facilitating accurate diagnosis. The reader will learn about the current state of brachial plexus MRN, including recent advances and future directions, and gain knowledge about the adult and pediatric brachial plexopathies that can be characterized using these techniques.Areas Covered: The review details recent developments in brachial plexus MRN, including increasing availability of 3.0-T MR scanners at both private and academic diagnostic imaging centers, as well as the advent of multiple new vascular and fat signal suppression techniques. A literature search of PubMed and SCOPUS was used as the principal source of information gathered for this review.Expert Opinion: Refinement of fat-suppression, 3D techniques and diffusion MR imaging modalities has improved the accuracy of MRN, rendering it as a useful adjunct to clinical findings during the evaluation of suspected brachial plexus lesions.

Conformational Engineering of HIV-1 Env Based on Mutational Tolerance in the CD4 and PG16 Bound States.

HIV-1 infection is initiated by viral Env engaging the host receptor CD4, triggering Env to transition from a "closed" to "open" conformation during the early events of virus-cell membrane fusion. To understand how Env sequence accommodates this conformational change, mutational landscapes decoupled from virus replication were determined for Env from BaL (clade B) and DU422 (clade C) isolates interacting with CD4 or antibody PG16 that preferentially recognizes closed trimers. Sequence features uniquely important to each bound state were identified, including glycosylation and binding sites. Notably, the Env apical domain and trimerization interface are under selective pressure for PG16 binding. Based on this key observation, mutations were found that increase presentation of quaternary epitopes associated with properly conformed trimers when Env is expressed at the plasma membrane. Many mutations reduce electrostatic repulsion at the Env apex and increase PG16 recognition of Env sequences from clades A and B. Other mutations increase hydrophobic packing at the gp120 inner-outer domain interface and were broadly applicable for engineering Env from diverse strains spanning tiers 1, 2, and 3 across clades A, B, C, and BC recombinants. Core mutations predicted to introduce steric strain in the open state show markedly reduced CD4 interactions. Finally, we demonstrate how our methodology can be adapted to interrogate interactions between membrane-associated Env and the matrix domain of Gag. These findings and methods may assist vaccine design.IMPORTANCE HIV-1 Env is dynamic and undergoes large conformational changes that drive fusion of virus and host cell membranes. Three Env proteins in a trimer contact each other at their apical tips to form a closed conformation that presents epitopes recognized by broadly neutralizing antibodies. The apical tips separate, among other changes, to form an open conformation that binds tightly to host receptors. Understanding how Env sequence facilitates these structural changes can inform the biophysical mechanism and aid immunogen design. Using deep mutational scans decoupled from virus replication, we report mutational landscapes for Env from two strains interacting with conformation-dependent binding proteins. Residues in the Env trimer interface and apical domains are preferentially conserved in the closed conformation, and conformational diversity is facilitated by electrostatic repulsion and an underpacked core between domains. Specific mutations are described that enhance presentation of the trimeric closed conformation across diverse HIV-1 strains.

Mapping Interaction Sites on Human Chemokine Receptors by Deep Mutational Scanning.

Chemokine receptors CXCR4 and CCR5 regulate WBC trafficking and are engaged by the HIV-1 envelope glycoprotein gp120 during infection. We combine a selection of human CXCR4 and CCR5 libraries comprising nearly all of ∼7000 single amino acid substitutions with deep sequencing to define sequence-activity landscapes for surface expression and ligand interactions. After consideration of sequence constraints for surface expression, known interaction sites with HIV-1-blocking Abs were appropriately identified as conserved residues following library sorting for Ab binding, validating the use of deep mutational scanning to map functional interaction sites in G protein-coupled receptors. Chemokine CXCL12 was found to interact with residues extending asymmetrically into the CXCR4 ligand-binding cavity, similar to the binding surface of CXCR4 recognized by an antagonistic viral chemokine previously observed crystallographically. CXCR4 mutations distal from the chemokine binding site were identified that enhance chemokine recognition. This included disruptive mutations in the G protein-coupling site that diminished calcium mobilization, as well as conservative mutations to a membrane-exposed site (CXCR4 residues H792.45 and W1614.50) that increased ligand binding without loss of signaling. Compared with CXCR4-CXCL12 interactions, CCR5 residues conserved for gp120 (HIV-1 BaL strain) interactions map to a more expansive surface, mimicking how the cognate chemokine CCL5 makes contacts across the entire CCR5 binding cavity. Acidic substitutions in the CCR5 N terminus and extracellular loops enhanced gp120 binding. This study demonstrates how comprehensive mutational scanning can define functional interaction sites on receptors, and novel mutations that enhance receptor activities can be found simultaneously.

Magnetic Resonance Neurography in Chronic Lumbosacral and Pelvic Pain: Diagnostic and Management Impact-Institutional Audit.

BACKGROUND/OBJECTIVE: Low back and pelvic pain are among the most prevalent conditions worldwide, with major social and economic costs. The aim of this study was to evaluate the role of magnetic resonance neurography (MRN) of lumbosacral plexus in the management and outcomes of these patients with chronic pain. METHODS: Consecutive patients with chronic lumbosacral and pelvic pain referred for MRN over a year were included. Preimaging and postimaging clinical diagnosis and treatment, pain levels, and location were recorded. Pain-free survival was compared between treatments using a Cox proportional hazards model. RESULTS: A total of 202 patients with mean age 53.7 ± 14.8 years and a male/female ratio of 1:1.53 were included. Of these patients, 115 presented with radiculopathy (57%), 56 with pelvic pain (28%), and 31 with groin pain (15%). Mean initial pain level was 6.9 ± 1.9. Mean symptom duration was 4.21 ± 5.86 years. Of these patients, 143 (71%) had a change in management because of MRN. After MRN, reduction in pain levels was observed in 21 of 32 patients receiving conservative treatment (66%), 42 of 67 receiving injections (63%), and 27 of 33 receiving surgery (82%). Follow-ups were available in 131 patients. Median pain-free survival was 12 months. Patients treated with surgery had significantly lower pain recurrence than patients receiving other treatments in the same time frame (hazard ratio, 3.6; 95% confidence interval, 1.4-9.2; P = 0.0061). CONCLUSIONS: MRN use in chronic lumbosacral and pelvic pain led to a meaningful change in diagnosis and treatment. After MRN, conservative treatment and injections provided pain relief; however, patients benefited more from surgery than from any other treatment.

A new quantitative measure of disc degeneration.

BACKGROUND CONTEXT: The ability to adequately measure a phenomenon is critical to studying and understanding it. Since 1957, a variety of subjective visual grading methods have been used to assess disc degeneration, but these have been limited by gross ordinal scales and imprecision, as well as suboptimal reliability. Conceptually sound, objective, precise measurements are needed to advance knowledge of disc degeneration and its causes, progression, and consequences. PURPOSE: This study aimed to investigate the reliability and validity of a new system ("SpIn" for spine insight) to quantitatively measure lumbar disc degeneration or pathology. STUDY DESIGN: This is a measurement study using cross-sectional and longitudinal data. PATIENT SAMPLE: The subjects were 108 men from 35 to 63 years of age at baseline. OUTCOME MEASURES: SpIn measures were validated using age, Pfirrmann grade, and other magnetic resonance imaging (MRI)-based disc and vertebral measurements associated with degeneration. METHODS: The lumbar spine was imaged using a 1.5 T Magnetom MRI scanner at baseline and a 1.5 T Avanto scanner at 15-year follow-up, forming two scanner-age groups. After the disc was manually traced on mid-disc axial MR images, image analysis software automatically measured distances, areas, and mean signal of regions of interest to calculate the new ratio-based disc degeneration measurements (SpIn). Repeated measurements were conducted on 30 subjects to estimate intra- and inter-rater reliability. Univariate methods and multiple regression modeling were used to compare associations of SpIn values and Pfirrmann grade, as a reference standard, with age and other degenerative and morphologic changes over follow-up. The MRI data used in the study were collected with support from the National Institutes of Health (NIH) National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) and the Finnish Work Environment Fund. One author (TV) has a patent interest in SpIn. RESULTS: Intra-rater and inter-rater measurements for SpIn yielded correlation coefficients of at least 0.98. Associations with age were clearly weaker for Pfirrmann grade than for SpIn. The variance in age explained by axial SpIn values ranged from 15.0% to 23.4% (adjusted R2), depending on spinal level and scanner-age group, as compared with 5.9%-12.9% for Pfirrmann grade. Although both SpIn values and Pfirrmann grades were associated with familial aggregation, associations were generally higher with Pfirrmann grade. Baseline SpIn values and Pfirrmann grade were both associated with subsequent, structural degenerative changes in lumbar discs and vertebrae over the 15-year follow-up, but all associations were stronger with SpIn. CONCLUSIONS: SpIn provides a highly reliable, objective, continuous digital measurement of disc degeneration, which uses routinely acquired MRI and could benefit related research.

Agroterrorism: the risks to the United States food supply and national security.

Agroterrorism is a collective term that describes an intentional criminal attack against crops or mankind using viral, bacterial, fungal, or insect-borne agents. Agroterrorism also includes attacks against animals using infectious pathogens such as Burkholderia mallei (glanders), Bacillus anthracis (anthrax), viral avian influenza, foot and mouth disease, and several equine encephalitis viruses. Agents that could be used against crops include the causative agents of wheat blast, rice blast, rice brown spot disease, and wheat stem rust. The primary goal of terrorists using agroterrorism is to spread fear and cause massive economic loss. Subsequent goals include causing disease and death to humans and animals. The use of bioterrorism agents is a much more practical approach than using explosives, for example, to achieve those results since many of these biological agents are commonly found naturally in the environment and are difficult to detect with modern technology. The effective use of biological warfare dates back centuries and can still can be employed by terrorist groups, lone wolves, and political and religious groups to cause death and mayhem on a grand scale.

Lumbar spinal stenosis is a highly genetic condition partly mediated by disc degeneration.

Objective. Lumbar spinal stenosis is one of the most commonly diagnosed spinal disorders in older adults. Although the pathophysiology of the clinical syndrome is not well understood, a narrow central canal or intervertebral foramen is an essential or defining feature. The aim of the present study was to estimate the magnitude of genetic versus environmental influences on central lumbar spinal stenosis and to investigate disc degeneration and stature or bone development as possible genetic pathways.Methods. A classic twin study with multivariate analyses considering lumbar level and other covariates was conducted. The study sample comprised 598 male twins (147 monozygotic and 152 dizygotic pairs), 35-70 years of age, from the population-based Finnish Twin Cohort. The primary phenotypes were central lumbar stenosis as assessed qualitatively on magnetic resonance imaging (MRI) and quantitatively measured dural sac cross-sectional area. Additional phenotypes (to examine possible genetic pathways) included disc bulging and standing height, as an indicator of overall skeletal size or development.Results. The heritability estimate (h²) for qualitatively assessed central lumbar spinal stenosis on MRI was 66.9% (95% confidence interval [95% CI] 56.8,74.5). The broad-sense heritability estimate for dural sac cross-sectional area was 81.2% (95% CI 74.5, 86.1),with a similar magnitude of genetic influences across lumbar levels (h²=72.4­75.6). The additive genetic correlation of quantitatively assessed stenosis and disc bulging was extremely high. There was no indication of shared genetic influences between stenosis and stature.Conclusion. Central lumbar spinal stenosis and associated dural sac dimensions are highly genetic, and disc degeneration (bulging) appears to be one pathway through which genes influence spinal stenosis.

Impact of source data on the interpretation of contrast-enhanced magnetic resonance angiography of the lower limbs.

BACKGROUND: The primary purpose of this study is to examine whether use of source data is effective in increasing the number of arterial segments that can be interpreted from maximum intensity projections of lower limb MR angiograms. Correlation between sites of arterial disease and venous contamination was also measured. Interpretation of source data is performed routinely by radiologists, but the value of this has not been well studied with randomized studies. RESULTS: The proportion of segments visible above the knee was 87% using maximal intensity projection alone (MIP) and 88% when the MIP was combined with source data. The proportions were 67% for MIP and 72% for MIP plus source data below the knee. There was substantial agreement between presence of arterial disease and venous contamination in the calf and thigh. CONCLUSION: The use of source data increases the number of assessable segments, but not individuals, by a statistically significant but small amount (1.2%, p <0.05). This study supports the association between arterial disease and venous contamination.

Aging changes in lumbar discs and vertebrae and their interaction: a 15-year follow-up study.

BACKGROUND CONTEXT: Many studies have focused on either the intervertebral disc as a culprit in back pain problems, or the vertebral body, but very few studies have examined both structures and their relationship. PURPOSE: To measure the concordant changes in morphology of the discs and vertebrae during 5-, 10-, and 15-year follow-ups. STUDY DESIGN: Longitudinal study. PATIENT SAMPLE: Among a general population sample of 232 men that had been scanned in 1992-1993, 105 men were reexamined in 1997-1998 and 2007-2008. Mean age at the 15-year follow-up was 63 years. A confirmatory sample with 10 years follow-up was also included. METHODS: Scanners (1.5 Tesla) with surface coils were used at baseline and follow-up. Image analyzing software was used to measure distances and areas of interest of midsagittal and midaxial spine images. RESULTS: The disc heights decreased at 5 years by 3.4% (0.4 mm) and 3.3% (0.4 mm) and at 15 years by 8.7% (1.0 mm) and 11.3% (1.3 mm) in the upper and lower discs, respectively (p<.001). Although not clear after 5 years, vertebra heights increased in mean by 3.1% (0.8 mm) in the upper lumbar levels and by 4.7% (1.1 mm) in the lower vertebrae after 15 years (p<.001). Vertebra height increases were associated with disc narrowing (p=.001). The mean annual shortening of the lumbar spine L1-S1 block was 0.13 mm/y, which was in line with the mean standing height that decreased little (174.7 cm at baseline and 174.4 cm at the follow-up). CONCLUSIONS: Discs and vertebrae degenerate or remodel in concert: decreases in disc height appear to be compensated, in part, by accompanying increases in adjacent vertebra heights. The mechanism behind this novel finding and its implications require further study.

A comparison of film and computer workstation measurements of degenerative spondylolisthesis: intraobserver and interobserver reliability.

STUDY DESIGN: A comparison of measurements of degenerative spondylolisthesis made on film and on computer workstations. OBJECTIVE: To determine whether the 2 methodologies are comparable in some of the parameters used to assess lumbar degenerative spondylolisthesis. SUMMARY OF BACKGROUND DATA: Digital radiology has been replacing analog radiographs. In scoliosis, several studies have shown that measurements made on digital and analog films are similar and that they are also similar to those made on computer workstations. Such work has not been done in spondylolisthesis. METHODS: Twenty-four cases of lumbar degenerative spondylolisthesis were identified from our clinic practice. Three observers measured anterior displacement, sagittal rotation, and lumbar lordosis on digital films using the same protractor and pencil. The same parameters were measured on the same studies at clinical workstations. All measurements were repeated 2 weeks later. A statistician determined the intra and interobserver reliability of the 2 measurement methods and the degree of agreement between the 2 methods. RESULTS: The differences between the first and second readings did reach statistical significance in some cases, but none of them were large enough to be clinically meaningful. The interclass correlation coefficients (ICCs) were >or=0.80 except for one (0.67). The difference among the 3 observers was similarly statistically significant in a few instances but not enough to influence clinical decisions and with good ICCs (0.67 and better). Similarly, the differences in the 2 methods were small, and ICCs ranged from 0.69 to 0.98. CONCLUSION: This study supports the use of computer workstation measurements in lumbar degenerative spondylolisthesis. The parameters used in this study were comparable, whether measured on film or at clinical workstations.

Associations of 25 structural, degradative, and inflammatory candidate genes with lumbar disc desiccation, bulging, and height narrowing.

OBJECTIVE: To examine the allelic diversity of structural, inflammatory, and matrix-modifying gene candidates and their association with disc degeneration. METHODS: Subjects were 588 men ages 35-70 years. We investigated associations of single-nucleotide polymorphisms in AGC1 and in 12 collagen, 8 interleukin, and 4 matrix metalloproteinase genes with quantitative magnetic resonance imaging measurements of disc desiccation and disc bulging and height narrowing scores, after controlling for age and suspected risk factors. Analyses were performed using QTDT software. P values were derived from 1,000 permutations, and empirical P values for global significance also were applied. RESULTS: Twelve of the 99 variants in 25 selected candidate genes provided evidence of association (P < 0.05) with disc signal intensity in the upper and/or lower lumbar regions. Allelic variants of AGC1 (rs1042631; P = 0.001), COL1A1 (rs2075555; P = 0.005), COL9A1 (rs696990; P = 0.00008), and COL11A2 (rs2076311; P = 0.018) genes provided the most significant evidence of association with disc signal intensity. The same variants of AGC1 (P = 0.010) and COL9A1 (P = 0.014), as well as variants in the COL11A1 gene (rs1463035 [P = 0.004]; rs1337185 [P = 0.015]) were also associated with disc bulging, as was AGC1 with disc height narrowing (rs1516797; P = 0.005). In addition, 4 allelic variants in the immunologic candidate genes (rs2071375 in IL1A [P = 0.027]; rs1420100 in IL18RAP [P = 0.005]) were associated with disc signal intensity. CONCLUSION: Genetic variants account for interindividual differences in disc matrix synthesis and degradation. The accuracy of the quantitative disc signal intensity measurements we used likely enhanced our ability to observe these associations. Our findings shed light on possible mechanisms of degeneration and support the view that disc degeneration is a polygenetic condition.

The Twin Spine Study: contributions to a changing view of disc degeneration.

BACKGROUND CONTEXT: Disc degeneration was commonly viewed over much of the last century as a result of aging and "wear and tear" from mechanical insults and injuries. Thus, prevention strategies and research in lumbar degenerative changes and associated clinical conditions focused largely on mechanical factors as primary causes using an "injury model." The Twin Spine Study, a research program on the etiology and pathogenesis of disc degeneration, has contributed to a substantial revision of this view of determinants of lumbar disc degeneration. PURPOSE: To provide a review of the methods and findings of the Twin Spine Study project. STUDY DESIGN/SETTING: Narrative review of the Twin Spine Study. METHODS: The Twin Spine Study, which started in 1991, is a multidisciplinary, multinational research project with collaborators primarily in Canada, Finland, and the United States. The most significant investigations related to determinants of disc degeneration included occupational exposures, driving and whole-body vibration exposure, smoking exposure, anthropomorphic factors, heritability, and the identification of genotypes associated with disc degeneration. RESULTS: Among the most significant findings were a substantial influence of heredity on lumbar disc degeneration and the identification of the first gene forms associated with disc degeneration. Conversely, despite extraordinary discordance between twin siblings in occupational and leisure-time physical loading conditions throughout adulthood, surprisingly little effect on disc degeneration was observed. Studies on the effects of smoking on twins with large discordance in smoking exposure demonstrated an increase in disc degeneration associated with smoking, but this effect was small. No evidence was found to suggest that exposure to whole-body vibration through motorized vehicles leads to accelerated disc degeneration in these well-controlled studies. More recent results indicate that the effect of anthropometric factors, such as body weight and muscle strength on disc degeneration, although modest, appear in this work to be greater than those of occupational physical demands. In fact, some indications were found that routine loading may actually have some benefits to the disc. CONCLUSIONS: The once commonly held view that disc degeneration is primarily a result of aging and "wear and tear" from mechanical insults and injuries was not supported by this series of studies. Instead, disc degeneration appears to be determined in great part by genetic influences. Although environmental factors also play a role, it is not primarily through routine physical loading exposures (eg, heavy vs. light physical demands) as once suspected.

Genetic and environmental effects on disc degeneration by phenotype and spinal level: a multivariate twin study.

STUDY DESIGN: A classic twin study with multivariate analyses was conducted. OBJECTIVE: We aimed to further clarify the presence and magnitude of genetic influences on disc degeneration, and to better understand the phenomenon of disc degeneration through comparisons of genetic and environmental influences on specific degenerative signs and different lumbar levels. SUMMARY OF BACKGROUND DATA: Previous studies suggest a substantial genetic influence on disc degeneration, but raise important questions about which disc phenotypes are or are not largely genetically influenced and differential effects on spinal levels. METHODS: The study sample consisted of 152 monozygotic and 148 dizygotic male twin pairs, 35 to 70 years of age, from the population-based Finnish Twin Cohort. Lumbar magnetic resonance imaging was conducted with quantitative or qualitative assessments of disc signal, bulging, and height narrowing at each lumbar level. Data on possible confounding factors were obtained from an extensive, structured interview. Quantitative genetic modeling was conducted using MPlus. RESULTS: Heritability estimates varied from 29% to 54%, depending on the particular disc degeneration phenotype and lumbar level. The same genetic influences affected signal intensity and disc height (genetic correlations of -0.60- -0.66) or bulging (-0.71- -0.72) to a great degree at either the lower or upper lumbar levels and genetic influences on disc height narrowing and bulging were virtually the same. (0.92-0.97). Conversely, genetic correlations (and environmental correlations)were substantially lower for upper and lower lumbar levels, implying largely independent effects. CONCLUSION: Genetic and environmental influences on disc degeneration seem to be of similar importance. Disc signal, narrowing, and bulging had a primarily common genetic pathway, suggesting a common genetic etiopathogenesis. Conversely, genetic and environmental influences differed substantially for upper versus lower lumbar levels, emphasizing the importance of examining these levels separately in studies of associated genes, other constitutional factors, and environmental influences.

The prevalence and characteristics of thoracic magnetic resonance imaging findings in men.

STUDY DESIGN: A cross-sectional study of thoracic magnetic resonance image (MRI) findings. OBJECTIVE: To examine the prevalence of different thoracic MRI findings for T6-T12 and their associations with age and one another by level. SUMMARY OF BACKGROUND DATA: There is a dearth of descriptive epidemiology of thoracic MRI findings in the general population. METHODS: Thoracic MRIs of 524 men were assessed qualitatively and quantitatively for a variety of findings, including disc bulging, height and signal, vertebral deformities, endplate irregularities, osteophytes, and hemangiomas. Descriptive statistics, correlation coefficients and STATA's survey analysis were used. RESULTS: In the lower thoracic spine, 5.4% to 9.5% of the discs, depending on level, were qualitatively assessed as moderately to severely narrowed. Anterior bulging was more common than posterior, which was relatively rare and mild when present. Signal was lower in the midthoracic than lower discs. At least 1 moderate or severe vertebral deformity was found in 6.1% of the subjects, suggesting fracture, and hemangiomas were identified in 2.3% of subjects. Disc signal correlated most highly with age (r = 0.31-0.42). Qualitatively assessed disc height narrowing (r = 0.29-0.46) and quantitative disc height (r = 0.11-0.29) were associated with disc signal. Upper and lower endplate irregularities were associated with one another (r = 0.17-0.32), as were bulging and osteophytes, anteriorly (r = 0.35-0.61) and posteriorly (r = 0.26-0.45). CONCLUSION: Degenerative MRI findings beyond a mild grade were not commonly observed in the thoracic spine among 35-70-year-old men. Posterior bulges, in particular, were rare. The highest correlation with age existed for disc signal. Different MRI findings were associated with one another, but the magnitude of association varied by level. The effects of individual judgments and disc level on prevalence rates were apparent.