ANKH variants associated with ankylosing spondylitis: gender differences

Male spondyloarthritis patients and those with longer disease duration have less severe disc degeneration: propensity score-matched comparison

Objective

Using whole spine sagittal T2 MRI, we aimed to compare the severity and prevalence of disc degeneration (DD) in axial SpA patients vs the general population and to determine any association between spinal inflammation, structural changes, mobility and DD among SpA patients.

Methods

Two prospectively collected cohorts of SpA patients (n = 411) and the general population (n = 2007) were recruited. Eventually, 967 participants from the populational cohort and 304 participants from the SpA cohort were analysed. Two hundred and nineteen matched pairs were generated by propensity score matching. Imaging parameters, including Pfirrmann grading, disc herniation, high-intensity zone, Schmorl's node, Modic change and anterior marrow change were studied and compared from C2/3 to L5/S1. DD was defined as Pfirrmann grade 4 or 5. Demographic factors, including age, sex and BMI, were collected. Multivariable linear regression was used to determine the association between spinal inflammation [Spondyloarthritis Research Consortium of Canada (SPARCC) spine MRI index], structural changes [modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS)] and mobility (BASMI) with lumbar Pfirrmann score.

Results

SpA patients had lower prevalence of DD (P < 0.001). The disease stage-stratified regression model showed that SPARCC spinal MRI index was associated with higher lumbar Pfirrmann scores in early disease (β = 0.196, P = 0.044), whereas mSASSS was associated with lower lumbar Pfirrmann scores in later disease (β = -0.138, P = 0.038). Males had higher mSASSS (P < 0.001) and lower odds of whole spine DD (odds ratio = 0.622, P = 0.028).

Conclusion

SpA patients had lower DD severity than the general population. Males had higher mSASSSs, and increased mSASSS at later disease was associated with less severe DD.

Polymorphism rs10499194 of the TNFA1P3 gene is not associated with a predisposition to ankylosing spondylitis in the Russian cohort of patients

Background. Recently, numerous studies have shown that TNFAIP3 gene polymorphisms have been associated with susceptibility to certain autoimmune inflammatory diseases, including systemic lupus erythematosus, scleroderma, rheumatoid arthritis and psoriasis. However, the results of studies devoted to the study of associations between TNFAIP3 gene polymorphisms and the risk of ankylosing spondylitis (AS) are ambiguous and few.The aim of the study was to study the possible association of hs10499194 polymorphism of the TNFAIP3 gene with a predisposition to AS and its clinical phenotypes.Material and methods. The rs10499194 S/T polymorphism of the TNFA1P3 gene was studied in two hundred patients with AS (130 men and 70 women). All patients were diagnosed with AS, according to the modified New York criteria, 1984 and high activity of the disease. Demographic and clinical-serological characteristics were studied in all patients. The average age of patients was 39.4±12.6 years; the average duration of the disease was 15.0±10.6 years. Out of 200 patients, 175 (87.5%) were seropositive for HLA-B27 antigen. Extra axial arthritis was detected in 125 (62.5%) patients, 148 (74.0%) had enthesitis, 137 (68.5%) had coxitis. The polymorphism rs10499194 of the TNFAIP3 gene was studied using an allelespecific polymerase chain reaction in real time (PCR-RV) using the Synthol kit.Results. The analysis of the frequencies of genotypes and alleles did not show significant differences with the control group. Stratification by sex, age, and clinical manifestations showed an association of the CT genotype with an increased risk of AS among men (OR=2.24; p=0.010), the TT genotype and the T allele with a high risk of predisposition to the development of extra axillary peripheral arthritis (OR=3.94; p=0.019 and OR=1.64; p=0.027 respectively). The BASDAI index was statistically significantly higher in carriers of the TT genotype compared to the CT genotype (p=0.002).Conclusion. The present study confirmed the association of the genetic polymorphism rs10499194 of the TNFAIP3 gene with AS. Stratification by gender and clinical manifestations showed an association of the CT genotype with an increased risk of AS among men, the TT genotype and the T allele with a high risk of predisposition to the development of extra axillary peripheral arthritis and a high BASDAI index in carriers of the TT genotype.

The role of LCN2 and LCN2-MMP9 in spondylitis radiographic development: gender and HLA-B27 status differences

Background

Male HLA-B27-positive radiographic-axial spondyloarthritis (r-axSpA) patients are prone to have severe spinal radiographic progression, but the underlying mechanisms are unclear. We recently showed that persistently elevated Lipocalin 2 (LCN2; L) reflects sacroiliac joint (SIJ) inflammation. LCN2 binds to MMP9. Concomitant elevation of L and LCN2-MMP9 (LM) was detected in many inflammatory diseases. We asked whether L and LM play similar roles in r-axSpA pathogenesis.

Methods

We analyzed 190 axSpA patients (123 radiographic and 67 non-radiographic axSpA) who had no detectable circulating Oncostatin M, to avoid complications due to cross-talk between pathways. L and LM levels from a single blood sample of each patient were measured and were correlated with MRI and modified stoke AS (mSASS) scoring. Association of elevated L (L+) or concurrent L+ and elevated LM (LM+) patterns with B27 status and gender were assessed.

Results

In L+LM+ axSpA patients, both L and LM levels correlated with MRI SPARCC SIJ scores, but only LM levels correlated with MRI Berlin Spine Scores, suggesting LM is a biomarker for both SIJ and spinal inflammation. Among patients with minimal spinal ankylosis (mSASSS < 10), 65% of male r-axSpA patients are L+LM+, while 30% and 64% of female patients are L+LM+ and L+, respectively, supporting the role of LM with disease progression. In B27+ L+LM+ male patients, both L and LM (but not CRP) levels correlate with mSASSS. B27 positivity and maleness have additive effects on spondylitis progression, suggesting concurrent high L and LM elevations are associated with B27+ male patients having more significant radiographic damage. L+ B27-negative male patients or L+ female patients are more likely to have milder disease.

Conclusion

L and LM are informative biomarkers for SIJ and spinal inflammation, as well as for ankylosing development in r-axSpA patients. Distinctive L+LM+ or L+ patterns not only could distinguish clinically aggressive vs milder course of disease, respectively, but also provide an explanation for B27-positive male patients being the most susceptible to severe ankylosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-022-02854-2.

Does Gender Impact a Diagnosis of Ankylosing Spondylitis?

Objective

The study objective was to explore differences in ankylosing spondylitis (AS) diagnosis experiences between men and women by examining the coding of health events over the 2 years preceding AS diagnosis.

Methods

Claims data (January 2006–April 2019) from the MarketScan databases were examined. Patients who had received two or more AS diagnoses at least 30 days apart and had at least 2 years of insurance enrollment before their first AS diagnosis were analyzed. Men were matched 1:1 to women by age, diagnosis date, insurance type, and enrollment duration. Health events (diagnosis and provider codes) were examined over 2 years before AS diagnosis and stratified by gender. Data were analyzed using univariate χ² tests.

Results

Among 7744 patients, 274 of 1906 AS‐related codes showed statistically significant differences between men and women. Women received more diagnosis codes than men across diagnoses and providers; the largest difference in diagnosis codes among women versus men was in peripheral symptom coding (57.7% vs. 43.9%, respectively). More women than men received diagnosis codes for depression (21.2% vs. 9.8%) and other musculoskeletal symptoms (52.8% vs. 40.0%); only gout was more common in men (6.5%) than in women (2.2%). Among men, backache codes gradually increased 12 months before AS diagnosis, whereas axial and sacroiliitis coding increased sharply immediately before diagnosis. The greatest difference in physician types visited was for rheumatologists: 64.2% of women had visits compared with 45.1% of men.

Conclusion

Further investigation into the dissimilarities in diagnostic experiences between men and women is needed to determine whether differences are due to disease phenotype or potential cognitive bias influencing diagnostic decision‐making.

Integrative blood-derived epigenetic and transcriptomic analysis reveals the potential regulatory role of DNA methylation in ankylosing spondylitis

Background

The currently known risk loci could explain a small proportion of the heritability of ankylosing spondylitis (AS). Epigenetics might account for the missing heritability. We aimed to seek more novel AS-associated DNA methylation alterations and delineate the regulatory effect of DNA methylation and gene expression with integrated analysis of methylome and transcriptome.

Methods

Epigenome-wide DNA methylation and mRNA expression were profiled in peripheral blood mononuclear cells (PBMCs) from 45 individuals (AS: health controls (HCs) = 30:15) with high-throughput array. The methylome was validated in an independent cohort (AS: HCs = 12:12). Pearson correlation analysis and causal inference tests (CIT) were conducted to determine potentially causative regulatory effects of methylation on mRNA expression.

Results

A total of 4794 differentially methylated positions (DMPs) were identified associated with AS, 2526 DMPs of which were validated in an independent cohort. Both cohorts highlighted T cell receptor (TCR) signaling and Th17 differentiation pathways. Besides, AS patients manifested increased DNA methylation variability. The methylation levels of 158 DMPs were correlated with the mRNA expression levels of 112 genes, which formed interconnected network concentrated on Th17 cell differentiation and TCR signaling pathway (LCK, FYN, CD3G, TCF7, ZAP70, CXCL12, and PLCG1). We also identified several cis-acting DNA methylation and gene expression changes associated with AS risk, which might regulate the cellular mechanisms underlying AS.

Conclusions

Our studies outlined the landscapes of epi-signatures of AS and several methylation-gene expression-AS regulatory axis and highlighted the Th17 cell differentiation and TCR signaling pathway, which might provide innovative molecular targets for therapeutic interventions for AS.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-021-02697-3.

Clinical Manifestations and Diagnosis of Axial Spondyloarthritis

BACKGROUND

Axial spondyloarthritis (axSpA) is a chronic, rheumatic disease characterized by inflammation of the sacroiliac joint, spine, and entheses. Axial spondyloarthritis affects up to 1.4% of adults in the United States and is associated with decreased quality of life, increased mortality, and substantial health care-related costs, imposing a high burden on patients, their caregivers, and society.

SUMMARY OF WORK

Diagnosing axSpA can be difficult. In this review, we seek to help rheumatologists in recognizing and diagnosing axSpA.

MAJOR CONCLUSIONS

A discussion of challenges associated with diagnosis is presented, including use and interpretation of imaging, reasons for diagnostic delays, differences in disease presentation by sex, and differential diagnoses of axSpA.

FUTURE RESEARCH DIRECTIONS

The early diagnosis of axSpA and advances in available therapeutic options have improved patient care and disease management, but delays in diagnosis and treatment remain common. Additional research and education are critical for recognizing diverse axSpA presentations and optimizing management early in the course of disease.

Genetics, Epigenetics, and Gender Impact in Axial-Spondyloarthritis Susceptibility: An Update on Genetic Polymorphisms and Their Sex Related Associations

Spondyloarthritis (SpA) is a group of chronic inflammatory rheumatic disease that can be divided into predominantly axial or predominantly peripheral involvement, with or without associated psoriasis, inflammatory bowel disease or previous infection. Axial SpA (axSpA) encompasses ankylosing spondylitis (AS) with radiological sacroiliitis, and a type without radiographic sacroiliitis, called “non-radiographic axial SpA” (nr-axSpA). Males and females show large differences in their susceptibility to SpA, such as distinctions in clinical patterns, phenotypes and in therapeutical response, particularly to TNF inhibitors (TNFi). Several studies indicate that AS women have doubled risk to failure TNFi compared with males. This diversity in drugs’ efficacy among women and men may be caused by differences in the balance of sex hormones and in gene-specific expression likely triggered by X-chromosome instability and gene-specific epigenetic modifications. Evidence reported that polymorphisms in microRNAs on X- and other chromosomes, such as miR-146a, miR-155, miR-125a-5p, miR-151a-3p and miR-22-3p, miR-199a-5p could be involved in the different clinical presentation of SpA, as well as disease activity. In addition, association with non−response to TNFi treatment and presence of IRAK3 and CHUCK genes in SpA patients was recently detected. Finally, polymorphisms in genes involved in IL-23/IL-17 pathway, such as in drug pharmacodynamics and pharmacokinetics may have a role in response to TNFi, IL17i, and IL23i. A major understanding of genomic variability could help in the development of new therapeutic targets or in taking advantages of different mechanisms of action of biological drugs. Moving from the multifactorial etiology of disease, the present review aims at evaluating genetic and epigenetic factors and their relationship with sex and bDMARDs response, helping to investigate the different expression among males and females of genes on X- and other chromosomes, as well as mi-RNA, to highlight relationships between sex and occurrence of specific phenotypes and symptoms of the disease. Moreover, the role of the epigenetic modification in relation to immune-regulatory mechanisms will be evaluated.

Gender Differences in Disease Activity and Impact in Axial Spondyloarthritis

Ankylosing spondylitis (AS), characterized by inflammatory back pain and sacroiliitis on radiography, was traditionally considered a condition predominant in men. Since the introduction of the 2009 Assessment in Spondyloarthritis international Society classification criteria¹ aiming to facilitate earlier classification of cases without radiographic sacroiliitis, more women have been classified as having axial spondyloarthritis (axSpA).

IL-33 Gene Polymorphisms as Potential Biomarkers of Disease Susceptibility and Response to TNF Inhibitors in Rheumatoid Arthritis, Ankylosing Spondylitis, and Psoriatic Arthritis Patients

Objective

Rheumatoid arthritis (RA), ankylosing spondylitis (AS), and psoriatic arthritis (PsA) belong to inflammatory rheumatic diseases, the group of conditions of unknown etiology. However, a strong genetic component in their pathogenesis has been well established. A dysregulation of cytokine networks plays an important role in the development of inflammatory arthritis. Interleukin 33 (IL-33) is a recently identified member of the IL-1 family. To date, the significance of IL-33 in inflammatory arthritis has been poorly studied. This research aimed to investigate the potential of IL-33 gene polymorphisms to serve as biomarkers for disease susceptibility and TNF inhibitor response in RA, AS, and PsA patients.

Materials and Methods

In total, 735 patients diagnosed with RA, AS, and PsA and 229 healthy individuals were enrolled in the study. Genotyping for three single nucleotide polymorphisms (SNPs) within the IL-33 gene, namely, rs16924159 (A/G), rs10975519 (T/C), and rs7044343 (C/T), was performed using polymerase chain reaction amplification employing LightSNiP assays.

Results

In the present study, the IL-33 rs10975519 CC genotype was associated with a decreased risk of developing RA in females, while the IL-33 rs16924159 polymorphism was associated with the efficacy of anti-TNF therapy and clinical parameters for RA and AS patients. The IL-33 rs16924159 AA genotype correlated with higher disease activity and worse clinical outcomes in RA patients treated with TNF inhibitors, and AS patients carrying the IL-33 rs16924159 AA genotype had higher disease activity and a worse response to anti-TNF therapy. That indicates a deleterious role of the IL-33 rs16924159 AA genotype in the context of RA, as well as AS.

Conclusions

The obtained results suggest that IL-33 gene polymorphisms might be potential candidate biomarkers of disease susceptibility and anti-TNF treatment response in patients with inflammatory rheumatic diseases.

Sex and gender differences in axial spondyloarthritis: myths and truths

Mounting evidence reveals evident sex differences in physiology, disease presentation and response to medication in axial SpA (axSpA). Unfortunately these data are often neglected in clinical practice and research. In this review, myths that still exist on diagnosis, disease manifestation and drug effectiveness were argued against data of the most recent literature. The aim is to increase awareness of sex differences in the clinical aspects of axSpA.

Genetics and the axial spondyloarthritis spectrum

The axial SpAs (axSpAs) are clearly clinically a heterogeneous set of diseases with markedly varying extra-articular features. These diseases are all highly heritable and have overlapping but differing genetic origins. Shared features include association with HLA class I alleles and genes of the IL-23 pathway, among other things. Significant differences do exist however, both in the genetic loci involved and at specific loci in the individual genetic variants associated with each disease. These similarities and differences are of great interest in regards to disease pathogenesis and treatment development, although individually they are too small in effect to be of prognostic or diagnostic value. Polygenic risk scores, which capture a high proportion of the genetic variation between disorders, have been shown to have clinically useful discriminatory capacity in axSpA. This suggests they have the potential to enable improved disease classification, incorporating basic pathogenic features such as genomics, and ultimately benefitting clinical care. The aim of this article is to review the genetic characteristics of the spectrum of axSpAs and to discuss how this influences our understanding of the disease pathogenesis and the clinical implications of this understanding.

Ankylosis progressive homolog upregulation inhibits cell viability and mineralization during fibroblast ossification by regulating the Wnt/β‑catenin signaling pathway

Ankylosis progressive homolog (ANKH) is associated with fibroblast ossification in ankylosing spondylitis (AS). As the human ANKH gene is poorly characterized relative to its murine counterpart, the aim of the present study was to examine ANKH expression in ligament tissue isolated from patients with AS and the role played by this gene in AS‑associated fibroblast ossification. Fibroblasts were isolated from ligament tissue collected from patients with AS and ligament tissue from individuals with spinal cord fractures, then cultured. Fibroblasts from patients with AS were subsequently transfected with an ANKH overexpression vector, while those collected from individuals with spinal cord fractures were transfected with small interfering RNA specific for ANKH. Cell viability, apoptosis and mineralization were analyzed using MTT assays, flow cytometry and Alizarin Red staining, respectively. Furthermore, ANKH mRNA and protein expression levels were analyzed using reverse transcription‑quantitative PCR and western blotting analysis, respectively. The expression levels of osteogenesis markers, including alkaline phosphatase, osteocalcin, Runt‑related transcription factor 2, c‑Myc, as well as the β‑catenin signaling protein, were also determined using western blotting. The results of the present study revealed that ANKH protein expression levels were downregulated in AS total ligament tissue extract, compared with spinal fracture ligament. Moreover, the fibroblasts derived from patients with AS exhibited an increased viability and reduced apoptosis rates, compared with the fibroblasts from patients with spinal fracture. Notably, ANKH overexpression inhibited viability, mineralization and ossification, increased the phosphorylation of β‑catenin and downregulated β‑catenin and c‑Myc protein expression levels in fibroblasts from patients with AS. In addition, ANKH overexpression increased the ratio of p‑β‑catenin/β‑catenin in fibroblasts from patients with AS. By contrast, ANKH silencing in fibroblasts from patients with spinal fracture resulted in the opposite effect. In conclusion, the findings of the present study suggested that ANKH may inhibit fibroblast viability, mineralization and ossification, possibly by regulating the Wnt/β‑catenin signaling pathway.

Understanding differences between men and women with axial spondyloarthritis

Axial spondyloarthritis (axSpA) is a chronic inflammatory immune-mediated disease resulting in inflammatory low back pain and other inflammatory manifestations in peripheral joints and entheses. AxSpA encompasses both ankylosing spondylitis (AS), in which patients present with definitive sacroiliitis visible on radiographic imaging, as well as nonradiographic axSpA (nr-axSpA), in which such changes may not be discernable. Emerging evidence suggests that women and men experience axSpA differently. Although the prevalence of AS is approximately 2- to 3- fold higher in men than in women, nr-axSpA occurs with roughly equal frequency in women and men. The goal of this review is to increase awareness of sex differences in axSpA by exploring the distinct manifestations of disease and disease characteristics in women, the overall clinical burden, recommendations for diagnosis, and potential treatment options. We summarize and contextualize the results of recent studies that illuminate sex differences in nr-axSpA and AS, including differences in disease manifestation and progression. It is important that sex differences in axSpA are understood and considered when diagnosing and treating the spectrum of axSpA, including AS and nr-axSpA.

Insight into the Quality of Life of Patients with Ankylosing Spondylitis: Real-World Data from a US-Based Life Impact Survey

INTRODUCTION

We aim to assess the real-world, US patient-reported impact of ankylosing spondylitis (AS) on quality of life (QOL) across physical, discomfort, social, and emotional domains.

METHODS

Demographic and QOL data were collected from a random sample of patients associated with the Spondylitis Association of America (SAA) from July to December 2017. QOL measures were based on the Evaluation of Ankylosing Spondylitis Quality of Life (EASi-QoL) questionnaire. The survey evaluated AS impact on the physical domain on the day of survey participation and impact on the discomfort, social, and emotional domains within the week before participation. A 3:1 (male to female) weighting was performed to reflect the reported prevalence of AS in US adults.

RESULTS

Of 820 respondents who completed the survey, 716 self-reported receiving an AS diagnosis from their doctor and were included in this analysis (mean age, 55.5 years; 46.9% male). The mean total EASi-QoL score was 28.9 (weighted); overall, 33.7%, 31.7%, and 34.7% of respondents, respectively, reported a low (EASi-QoL score 0-17), a medium (18-35), and a high (≥ 36) impact of AS on QOL. The physical domain was most impacted; 41.9% of respondents had an EASi-QoL score ≥ 10 (weighted). Women were significantly more likely than men to report a high impact of AS on all QOL domains. Biologic users reported an impact on QOL comparable with the impact on QOL of nonsteroidal anti-inflammatory drug use. AS also impacted lifestyle characteristics, including career choice and sports participation.

CONCLUSION

AS negatively impacted all QOL domains analyzed. The incorporation of subjective measures of disease into disease evaluation should be considered.

FUNDING

Novartis Pharmaceuticals Corporation and UCB, Inc. Plain language summary available for this article.

Application of machine learning in the diagnosis of axial spondyloarthritis

PURPOSE OF REVIEW

In this review article, we describe the development and application of machine-learning models in the field of rheumatology to improve the detection and diagnosis rates of underdiagnosed rheumatologic conditions, such as ankylosing spondylitis and axial spondyloarthritis (axSpA).

RECENT FINDINGS

In an attempt to aid in the earlier diagnosis of axSpA, we developed machine-learning models to predict a diagnosis of ankylosing spondylitis and axSpA using administrative claims and electronic medical record data. Machine-learning algorithms based on medical claims data predicted the diagnosis of ankylosing spondylitis better than a model developed based on clinical characteristics of ankylosing spondylitis. With additional clinical data, machine-learning algorithms developed using electronic medical records identified patients with axSpA with 82.6-91.8% accuracy. These two algorithms have helped us understand potential opportunities and challenges associated with each data set and with different analytic approaches. Efforts to refine and validate these machine-learning models are ongoing.

SUMMARY

We discuss the challenges and benefits of machine-learning models in healthcare, along with potential opportunities for its application in the field of rheumatology, particularly in the early diagnosis of axSpA and ankylosing spondylitis.

Real-World Patient Experience on the Path to Diagnosis of Ankylosing Spondylitis

Introduction

We describe the journey to diagnosis of ankylosing spondylitis (AS) from the patient perspective and examine differences in this journey by sex.

Methods

US adults aged ≥ 18 years with a self-reported AS diagnosis were recruited online through CreakyJoints, a patient support community, and ArthritisPower, a patient research registry. Respondents completed a web-based survey on sociodemographics, disease burden, and diagnosis history. Results were stratified by sex and time to diagnosis using two-sample t tests and χ² tests, respectively, to observe differences across the groups; P < 0.05 was considered statistically significant.

Results

Among 235 respondents, 174 (74.0%) were female. Mean (SD) ages of female and male respondents were 48.6 (10.6) and 53.1 (10.3) years, respectively. From the time respondents began seeking medical attention, 87 were diagnosed within ≤ 1 year, 71 in 2–9 years, and 77 after ≥ 10 years. Symptoms that led respondents to seek treatment were back pain (73.2%) and joint pain (63.8%); fatigue and difficulty sleeping were more common among respondents with longer times to diagnosis. During the diagnosis process, men with AS tended to receive quicker AS diagnosis compared with women. Overall, commonly reported initial diagnoses among respondents with longer time to AS diagnosis included back problems and psychosomatic disorders. Significantly more women reported misdiagnoses of fibromyalgia (20.7 vs. 6.6%) and psychosomatic disorders (40.8 vs. 23.0%) compared with men.

Conclusions

Diagnosis delays and misdiagnoses were common among respondents with AS. Increasing awareness about AS among referring providers may minimize diagnosis delay.

Funding

Novartis Pharmaceuticals Corporation.

Plain Language Summary

Plain language summary available for this article.

Electronic Supplementary Material

The online version of this article (10.1007/s40744-019-0153-7) contains supplementary material, which is available to authorized users.

Gender Differences in Axial Spondyloarthritis: Women Are Not So Lucky

PURPOSE OF REVIEW

Ankylosing spondylitis (AS) was historically seen as a predominantly male disease. However, more recent data showed a more homogenous sex prevalence. Unfortunately, in many studies in axial spondyloarthritis (axSpA), the number of women included is low and the analyses are often not stratified for gender distribution. The purpose of this review is to aggregate the existing data on gender differences in axSpA in order to increase the awareness that female axSpA patients are still under-recognized.

RECENT FINDINGS

Several studies considering gender differences revealed that female axSpA patients had different disease manifestations due to different immunological, hormonal, and genetic responses. For instance, allelic frequencies of the AHNK-gene and tissue non-specific alkaline phosphatase (TNAP) haplotypes differed between men and women with ankylosing spondylitis (AS). In addition, different levels of tumor necrosis factor (TNF), interleukins IL-6, IL-17, and IL-18, were found between the two sexes. Furthermore, female patients show a higher diagnostic delay compared to males. Several studies indicate a higher frequency of extra-articular manifestations (EAM) in female axSpA patients, such as enthesitis, psoriasis, and inflammatory bowel disease (IBD), whereas acute anterior uveitis is more prevalent in male patients. Male AS patients more frequently show a higher Bath Ankylosing Spondylitis Radiology Index (BASRI) scores and modified Stoke Ankylosing Spondylitis Spine Scores (mSASSS) than females, which indicates that males have higher radiological damage and radiographic progression. However, disease activity (BASDAI) and quality of life (AsQol) scores are significantly higher in women, and more importantly, they have significantly lower response rates to treatment with TNF inhibitors (TNFi) and a significantly lower drug adherence. Despite the fact that men with axial SpA have a worse radiologic prognosis, women have a high disease burden, in part because they have a longer delay in diagnosis, higher disease activity, and significantly less responsiveness to treatment with TNFi.

Structural biology of solute carrier (SLC) membrane transport proteins

The human solute carriers (SLCs) comprise over 400 different transporters, organized into 65 families ( http://slc.bioparadigms.org/ ) based on their sequence homology and transport function. SLCs are responsible for transporting extraordinarily diverse solutes across biological membranes, including inorganic ions, amino acids, lipids, sugars, neurotransmitters and drugs. Most of these membrane proteins function as coupled symporters (co-transporters) utilizing downhill ion (H⁺ or Na⁺) gradients as the driving force for the transport of substrate against its concentration gradient into cells. Other members work as antiporters (exchangers) that typically contain a single substrate-binding site with an alternating access mode of transport, while a few members exhibit channel-like properties. Dysfunction of SLCs is correlated with numerous human diseases and therefore they are potential therapeutic drug targets. In this review, we identified all of the SLC crystal structures that have been determined, most of which are from prokaryotic species. We further sorted all the SLC structures into four main groups with different protein folds and further discuss the well-characterized MFS (major facilitator superfamily) and LeuT (leucine transporter) folds. This review provides a systematic analysis of the structure, molecular basis of substrate recognition and mechanism of action in different SLC family members.

Single nucleotide polymorphisms of autophagy-related 16-like 1 gene are associated with ankylosing spondylitis in females: a case-control study

AIMS

To investigate the associations of autophagy-related 16-like 1 (ATG16L1) gene single nucleotide polymorphisms (SNPs) with ankylosing spondylitis (AS) in a Chinese Han population.

METHODS

Six hundred and forty-nine AS patients from the First Affiliation Hospital of Anhui Medical University and 628 matched controls were selected. Genotyping for five SNPs in the ATG16L1 gene (rs4663421, rs2241880, rs4663396, rs6758317 and rs6431655) was performed using the improved multiplex ligase detection reaction (iMLDR) method. Haplotypes were built after linkage disequilibrium (LD) analysis. All analyses were stratified by gender.

RESULTS

Significant differences in the genotype frequencies at rs4663421 were found between female AS patients and female controls (P = 0.033). The frequencies of allele G of rs4663421 and allele C of rs6758317 were lower in AS patients than controls (odds ratio [OR] = 0.391, 95% CI = 0.175-0.876, P = 0.019; OR = 0.499, 95% CI = 0.263-0.949, P = 0.032, respectively) in females. However, no association remained significant after Bonferroni correction. rs4663396 and rs6758317 have been tested in high LD, and were used to construct three haplotypes: ht1 (CC), ht2 (TT) and ht3 (CT). The frequency of ht2 (TT) haplotype was higher in AS patients than controls (OR = 2.003, 95% CI = 1.053-3.808, P = 0.032) in females; similarly, no association existed after Bonferroni correction.

CONCLUSIONS

Two SNPs (rs4663421 and rs6758317) and the TT haplotype of the ATG16L1 gene are possibly associated with AS susceptibility in a Chinese Han female population.

Gender differences in axial spondyloarthritis

Within the concept of axial spondyloarthritis (axSpA), relevant differences between men and women have been described for patients with the radiographic disease form [ankylosing spondylitis (AS)]. The subjective perception of disease activity (spinal and peripheral pain, fatigue, morning stiffness) has been shown to be higher in female than in male patients. Moreover, women experience more functional limitations and a lower quality of life, despite lower degrees of radiographic spinal damage. Peripheral clinical involvement (arthritis and enthesitis) is, additionally, more predominant in women. On the other hand, a higher level of objective signs of inflammation (C-reactive protein, erythrocyte sedimentation rate, magnetic resonance imaging of sacroiliac joints and spine) has been reported in men. Whether these differences might explain the better response to treatment with anti-tumor necrosis factor agents observed in male patients remains unclear. The underlying causes of the discrepancies are still unknown and genetic, environmental, cultural and/or societal factors may be involved. While AS is still more prevalent in men in a ratio of 2-3:1, the prevalence of males and females in patients with axSpA without radiographic sacroiliac damage is similar. Gender differences in this subgroup of patients have not been adequately addressed, and are particularly needed to further validate the Assessment of SpondyloArthritis international Society classification criteria.

Design, synthesis and evaluation of benzoisothiazolones as selective inhibitors of PHOSPHO1

We report the discovery and characterization of a series of benzoisothiazolone inhibitors of PHOSPHO1, a newly identified soluble phosphatase implicated in skeletal mineralization and soft tissue ossification abnormalities. High-throughput screening (HTS) of a small molecule library led to the identification of benzoisothiazolones as potent and selective inhibitors of PHOSPHO1. Critical structural requirements for activity were determined, and the compounds were subsequently derivatized and measured for in vitro activity and ADME parameters including metabolic stability and permeability. On the basis of its overall profile the benzoisothiazolone analogue 2q was selected as MLPCN probe ML086.

The genetic basis of ankylosing spondylitis: new insights into disease pathogenesis

Ankylosing spondylitis (AS) is a complex disease involving multiple risk factors, both genetic and environmental. AS patients are predominantly young men, and the disease is characterized by inflammation and ankylosis, mainly at the cartilage–bone interface and enthesis. HLA-B27 has been known to be the major AS-susceptibility gene for more than 40 years. Despite advances made in the past few years, progress in the search for non-human leukocyte antigen susceptibility genes has been hampered by the heterogeneity of the disease. Compared to other complex diseases, such as inflammatory bowel disease (IBD), fewer susceptibility loci have been identified in AS. Furthermore, non-major histocompatibility-complex susceptibility loci discovered, such as ERAP1 and IL23R, are likely contributors to joint inflammation. Identification and confirmation of functional variants remains a significant challenge of investigations involving genome-wide association studies (GWAS). It remains unclear why none of the AS-susceptibility genes identified in GWAS appear to be directly involved in the ankylosing process. Numerous reviews have recently been published on the genetics of AS. Therefore, aside from a brief summary of what AS GWAS has successfully achieved thus far, this review will focus on directions that could address unanswered questions raised by GWAS.

Aberrant chondrocyte hypertrophy and activation of β-catenin signaling precede joint ankylosis in ank/ank mice

OBJECTIVE

We assessed the role of Ank in the maintenance of postnatal articular cartilage using the ank/ank mouse (mice homozygous for progressive ankylosis).

METHODS

We analyzed ank/ank mice and wild-type littermates (8, 12, and 18 weeks old). Sections from decalcified, paraffin-embedded joints were stained with hematoxylin and eosin. Articular chondrocyte size and cartilage thickness were determined using morphometric methods. Immuno-histochemical staining was performed with anticollagen X, antitissue nonspecific alkaline phosphatase (TNAP), and anti-ß-catenin antibodies on fixed joint sections. Axin2 expression in paw joint lysates in wild-type versus ank/ank mice were compared using Western blot analysis.

RESULTS

In all age groups of normal mice studied, calcified cartilage (CC) chondrocyte areas were significantly larger than those of uncalcified cartilage (UC) chondrocytes. However, similar chondrocyte areas (UC vs CC) were found in 12-week and 18-week-old ank/ank mice, indicating that hypertrophic chondrocytes were present in the UC of these mutant mice. The ank/ank mice showed an increase in CC thickness. The ank/ank UC hypertrophic chondrocytes showed diffuse immuno-reactivity for collagen X and TNAP. Increased ß-catenin activation was demonstrated by nuclear localization of ß-catenin staining in ank/ank chondrocytes. Axin2 expression from paw lysates was downregulated in ank/ank mice.

CONCLUSION

We identified a previously unrecognized phenotype in the articular cartilage of ank/ank mice: collagen X-positive hypertrophic chondrocytes in the UC. It is possible that consequent to downregulation of axin2 expression, ß-catenin signaling was activated, leading to accelerated chondrocyte maturation and eventual ankylosis in ank/ank joints. Our studies shed new light on the contribution of a key signaling pathway in this model of joint ankylosis.

Urolithiasis in ankylosing spondylitis: Correlation with Bath ankylosing spondylitis disease activity index (BASDAI), Bath ankylosing spondylitis functional index (BASFI) and Bath ankylosing spondylitis metrology index (BASMI)

BACKGROUND

Increased incidence of renal stone has been reported in ankylosing spondylitis (AS), but unlike some well-known renal involvements, they have not been fully studied. The aim of this study was to investigate the association of AS with urolithiasis and also the relation between urinary stone and severity markers.

METHODS

One hundred-sixty three AS patients were included in a cross-sectional study from Iranian AS association, Iran Rheumatology Center and Rheumatology Clinic of Shariati Hospital in Tehran. Prevalence of urolithiasis in AS patients was compared with results of a nationwide survey in Iran. Bath ankylosing spondylitis disease activity index (BASDAI), bath ankylosing spondylitis functional index (BASFI) and bath ankylosing spondylitis metrology index (BASMI) were determined for assessment of disease severity.

RESULTS

Urolithiasis was observed in 11.7% of AS patients versus 5.7% of normal population (p=0.001). After the elimination of corticosteroid effect, the prevalence of urolithiasis was still higher in AS patients than normal population but without maintaining significant difference. Significant higher values of BASFI, BASMI, BASDAI scores were observed in AS with urolithiasis than AS without urolithiasis.

CONCLUSION

The results confirmed the association of AS with urolithiasis. However, this may be partly due to the effect of other factors such as corticosteroid. Moreover, urolithiais is accompanied with more severe diseases.

ANKH and susceptibility to and severity of ankylosing spondylitis

OBJECTIVE

Unconfirmed reports describe association of ankylosing spondylitis (AS) with several candidate genes including ANKH. Cellular export of inorganic pyrophosphate is regulated by the ANK protein, and mutant mice (ank/ank), which have a premature stop codon in the 3' end of the ank gene, develop severe ankylosis. We tested the association between single-nucleotide polymorphisms (SNP) in these genes and susceptibility to AS in a population of patients with AS. We investigated the role of these genes in terms of functional (BASFI) and metrological (BASMI) measures, and the association with radiological severity (mSASSS).

METHODS

Our study was conducted on 355 patients with AS and 95 ethnically matched healthy controls. AS was defined according to the modified New York criteria. Four SNP in ANKH (rs27356, rs26307, rs25957, and rs28006) were genotyped. Association analysis was performed using Cochrane-Armitage and linear regression tests for dichotomous and quantitative variables. Analyses of Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), BASFI, and mSASSS were controlled for sex and disease duration.

RESULTS

None of the 4 markers showed significant single-locus disease associations (p > 0.05), suggesting that ANKH was not a major determinant of AS susceptibility in our population. No association was observed between these SNP and age at symptom onset, BASDAI, BASFI, BASMI, or mSASSS.

CONCLUSION

These results confirm data in white Europeans that ANKH is probably not a major determinant of susceptibility to AS. ANKH polymorphisms do not markedly influence AS disease severity, as measured by BASMI and mSASSS.

Converging evidence for an association of ATP2B2 allelic variants with autism in male subjects

BACKGROUND

Autism is a severe developmental disorder, with strong genetic underpinnings. Previous genome-wide scans unveiled a linkage region spanning 3.5 Mb, located on human chromosome 3p25. This region encompasses the ATP2B2 gene, encoding the plasma membrane calcium-transporting ATPase 2 (PMCA2), which extrudes calcium (Ca2+) from the cytosol into the extracellular space. Multiple lines of evidence support excessive intracellular Ca2+ signaling in autism spectrum disorder (ASD), making ATP2B2 an attractive candidate gene.

METHODS

We performed a family-based association study in an exploratory sample of 277 autism genetic resource exchange families and in a replication sample including 406 families primarily recruited in Italy.

RESULTS

Several markers were significantly associated with ASD in the exploratory sample, and the same risk alleles at single nucleotide polymorphisms rs3774180, rs2278556, and rs241509 were found associated with ASD in the replication sample after correction for multiple testing. In both samples, the association was present in male subjects only. Markers associated with autism are all comprised within a single block of strong linkage disequilibrium spanning several exons, and the "risk" allele seems to follow a recessive mode of transmission.

CONCLUSIONS

These results provide converging evidence for an association between ATP2B2 gene variants and autism in male subjects, spurring interest into the identification of functional variants, most likely involved in the homeostasis of Ca2+ signaling. Additional support comes from a recent genome-wide association study by the Autism Genome Project, which highlights the same linkage disequilibrium region of the gene.

Gender and disease features in Moroccan patients with ankylosing spondylitis

This study was conducted to determine differences in ankylosing spondylitis (AS) between men and women in terms of clinical characteristics, biological features, structural severity and quality of life (QoL). A total of 130 consecutive AS patients fulfilling the modified New York criteria were included. Sociodemographic data were collected. The activity of disease was assessed by the Bath ankylosing spondylitis disease activity index (BASDAI) and the functional disability by the Bath Ankylosing spondylitis functional index (BASFI). Spinal mobility was measured using the occiput-to-wall distance, chest expansion, Schober index and the Bath Ankylosing Spondylitis Metrology Index (BASMI). The Bath Ankylosing Spondylitis Radiologic Index (BASRI) was used to evaluate structural damage. Fatigue was evaluated using a visual analogue scale and the QoL was measured by using the generic instrument SF-36. Laboratory tests included the erythrocyte sedimentation rate (ESR) and the C-reactive protein (CRP). In our sample, there were 87 (66.9%) men and 43 (33.1%) women. Women had significantly lower educational levels but there were no differences in socioeconomic status, age at onset, diagnosis delay, disease duration or treatments. Also, women had higher clinical disease activity (morning stiffness and BASDAI score), higher number of tender joints, more severe enthesitis and higher scores of fatigue (for all p ≤ 0.05). Moreover, hip involvement was more prevalent in men and the impairment of spinal mobility was significantly worse compared to women (for all p ≤ 0.001). Men had worse radiographic damage and lower scores in physical and social domains of QoL, but there were no differences in functional impairment scores. In this study, we noticed that AS presents differently according to gender in our patients. More longitudinal studies seem to be necessary to identify gender-related parameters of disease, thing that may help in diagnosis and therapeutic management of our AS patients.

Clinical and radiographic features of adult-onset ankylosing spondylitis in Korean patients: comparisons between males and females

The objective of this study was to investigate clinical and radiographic features and gender differences in Korean patients with adult-onset ankylosing spondylitis. Multicenter cross-sectional studies were conducted in the rheumatology clinics of 13 Korean tertiary referral hospitals. All patients had a confirmed diagnosis of ankylosing spondylitis according to the modified New York criteria. Clinical, laboratory, and radiographic features were evaluated and disease activities were assessed using the Bath ankylosing spondylitis disease activity index. Five hundred and five patients were recruited. The male to female ratio was 6.1:1. Average age at symptom onset was 25.4+/-8.9 yr and average disease duration was 9.6+/-6.8 yr. Males manifested symptoms at a significantly earlier age. HLA-B27 was more frequently positive in males. Hips were more commonly affected in males, and knees in females. When spinal mobility was measured using tragus-to-wall distance and the modified Schober's test, females had significantly better results. Radiographic spinal changes, including bamboo spine and syndesmophytes, were more common in males after adjustment of confounding factors. In conclusion, we observed significant gender differences in radiographic spinal involvement as well as other clinical manifestations among Korea patients with adult-onset ankylosing spondylitis. These findings may influence the timing of the diagnosis and the choice of treatment.

The genetic background of ankylosing spondylitis

It has long been known that the major histocompatibility complex (MHC) is essentially involved in genetic susceptibility to ankylosing spondylitis (AS). The HLA-B27 antigen has been accounted for 20 to 50% of the total genetic risk for this disease. However, susceptibility to AS cannot be fully explained by associations with the MHC. Recent studies including linkage analyses as well as candidate gene and, most recently, genome-wide association studies indicate significant associations of the interleukin-1 gene cluster, interleukin-23 receptor and ARTS1 genes as well as other possible loci with AS. In the murine model of proteoglycan-induced spondylitis, two susceptibility loci termed Pgis1 and Pgis2 were identified. Thus, AS is not a single-gene disease and the involvement of multiple non-MHC genes may account for the individual as well as geographical differences seen in AS.

Genetic basis of renal cellular dysfunction and the formation of kidney stones

Nephrolithiasis is a result of formation and retention of crystals within the kidneys. The driving force behind crystal formation is urinary supersaturation with respect to the stone-forming salts, which means that crystals form when the concentrations of participating ions are higher than the thermodynamic solubility for that salt. Levels of supersaturation are kept low and under control by proper functioning of a variety of cells including those that line the renal tubules. It is our hypothesis that crystal deposition, i.e., formation and retention in the kidneys, is a result of impaired cellular function, which may be intrinsic and inherent or triggered by external stimuli and challenges. Cellular impairment or dysfunction affects the supersaturation, by influencing the excretion of participating ions such as calcium, oxalate and citrate and causing hypercalciuria, hyperoxaluria or hypocitraturia. The production and excretion of macromolecular promoters and inhibitors of crystallization is also dependent upon proper functioning of the renal epithelial cells. Insufficient or ineffective crystallization modulators such as osteopontin, Tamm-Horsfall protein, bikunin, etc. are most likely produced by the impaired cells.

Spinal radiographic changes in ankylosing spondylitis: association with clinical characteristics and functional outcome

OBJECTIVE

To determine which patients with ankylosing spondylitis (AS) have radiographic spinal damage and to investigate the relation between radiographic spinal changes and limitations in physical function.

METHODS

A cross-sectional nationwide study in Belgium of patients with AS under the care of a rheumatologist. The treating physician completed a questionnaire including clinical disease manifestations and laboratory findings (HLA-B27 and C-reactive protein), and classified spinal radiographs into 3 categories: (1) no AS-related spinal abnormalities; (2) syndesmophytes; and (3) spinal ankylosis. Patients completed the Bath AS Disease Activity Index (BASDAI) and the Bath AS Functional Index (BASFI). Ordinal regressions were performed to quantify the relationship between clinical manifestations and spinal radiographic changes. Generalized linear models were computed to quantify relationships among clinical manifestations, radiographic spinal changes, and functioning (BASFI).

RESULTS

A total of 619 patients fulfilled modified New York criteria for definite AS and had evaluable radiographic data; 68% were male and disease duration was 17.5 (SD 12.2) years. Male sex, younger age at symptom onset, and hip involvement were associated with radiographic changes; but HLA-B27, peripheral arthritis, and extraarticular disease status (uveitis, psoriasis, and inflammatory bowel disease) were not. Older age, BASDAI, hip involvement, and spinal change contributed to BASFI; but sex, disease duration, peripheral arthritis, and extraarticular manifestations did not.

CONCLUSION

Radiographic spinal changes in patients with AS are seen more often in men and those with hip involvement. BASFI status indicates the influence of radiographic changes and hip involvement, but does not reflect the presence of peripheral arthritis and does not differ between men and women.

Animal models of spondyloarthritis

Animal models are available for the study of several different aspects of spondyloarthritis. The models include naturally occurring spontaneous disorders in primates and rodents, spontaneous disorders in transgenic or gene-deleted rodents and induced disorders in rodents. Areas of investigation to which these models contribute include the role HLA-B27, processes of spinal and peripheral joint inflammation and calcification, immune responses to candidate antigens and the role of TNF.

Anthropometric and bone-related biochemical factors are associated with different haplotypes of ANKH locus

BACKGROUND

The human homologue of the mouse progressive ankylosis (ANKH) gene is one of the key genetic factors involved in bone mineralization. Previous studies have shown that plasma levels of osteoprotegerin (OPG) and parathyroid hormone (PTH) are associated with the distal region of the ANKH gene, whereas skeletal size measurements are associated with the promoter region.

AIM

The present study examines the possible phenotype-haplotype specificity of the associations in these two gene regions.

SUBJECTS AND METHODS

The total sample consists of 1249 healthy individuals (mean age = 47.7, SD = 16.8) from 404 nuclear families. Fifteen interrelated anthropometric measurements were transformed into two principal components, reflecting body size and mass. Those, plus circulating levels of PTH and OPG, were subjected to association analysis, using transmission disequilibrium tests (TDTs) with ANKH gene. From 805 to 1150 individuals per SNP were genotyped.

RESULTS

In the proximal region (rs3006069-rs835154-rs835141), associations were found between the A-A-C haplotype and the first principal component reflecting body size (p < or = 0.048), whereas another haplotype, G-G-C, was associated with the first principal component, reflecting the body mass (p < or = 0.008). In the distal region of ANKH (rs39968-rs696294-rs875525), the A-A-C haplotype was found to be associated with OPG plasma levels (p < or = 0.001), whereas the G-A-C haplotype was associated with PTH circulating concentrations (p < or = 0.025).

CONCLUSION

Taken together, the results show discrimination between the corresponding regions and haplotypes, suggesting trait-specific gene variants that influenced bone-related phenotypic variation in the studied population.

The contribution of genes outside the major histocompatibility complex to susceptibility to ankylosing spondylitis

PURPOSE OF REVIEW

Recent data have presented several new nonmajor histocompatibility complex genes in predisposition to ankylosing spondylitis, which will be summarized here.

RECENT FINDINGS

A retrospective meta-analysis of three previous whole genome linkage scans confirmed a strong linkage at chromosome 16q and moderate linkage at sites on chromosomes 3, 10, and 19q, and a meta-analysis of studies of the interleukin-1 (IL-1) region genes in ankylosing spondylitis suggested the susceptibility to be conferred by the IL-1A gene. More recently, the use of genotyping chips, derived from the International Hapmap resource, which provides an extensive genomic coverage of large disease cohorts, have made it possible to conduct successful genome-wide association studies. One such study has led to the identification and validation of two new genes, IL23R and ARTS1, in ankylosing spondylitis pathogenesis.

SUMMARY

A tremendous amount of progress has been made with respect to understanding the genetic basis of ankylosing spondylitis. The recent identification of two new genes, ARTS1 and IL23R, and confirmation of IL-1A association further substantiate that ankylosing spondylitis is determined to a large extent by genes outside the major histocompatibility complex.

Renal calcium stones: insights from the control of bone mineralization

Extracellular pyrophosphate (PPi) plays a central role in the control of normal bone mineralization since it antagonizes inorganic phosphate in the promotion of hydroxyapatite deposition. Studies using knock-out mice have established the functional importance of PPi generation via nucleotide pyrophosphatase phosphodiesterases (NPP) and of PPi transmembrane transport by the progressive ankylosis (ANK) protein. Tissue non-specific alkaline phosphatase activity counteracts this by hydrolysis of PPi to inorganic phosphate. The molecular nature and transport function of ANK are reviewed. A close parallel is drawn between the controlled mineralization of bone and the prevention of abnormal calcium crystal deposition within the kidney, especially when concentrated urine is produced. Pyrophosphate is present in urine, and ANK is expressed in the cortical collecting duct where PPi transport to both the tubular lumen and the renal interstitium may occur. Pyrophosphate may also be generated here by nucleoside triphosphate diphosphohydrolases (NTPD2 and 3) together with NPP1. Alkaline phosphatase activity is restricted to the proximal nephron, remote from these sites of PPi generation, transport and function. The physiological importance of PPi generation and transport in preventing idiopathic calcium renal stone disease and nephrocalcinosis now needs to be established.

Contribution of the putative genetic factors and ANKH gene polymorphisms to variation of circulating calciotropic molecules, PTH and BGP

It is well known that regulation of calcium homeostasis in bone remodeling is one of the most crucial factors for maintaining healthy bones. Parathyroid hormone (PTH) is probably the most important hormone that participates in the bone remodeling process. Another important biochemical factor governing bone metabolism is osteocalcin (BGP). Although the physiological functions of both of these factors are well known, there is still very little known regarding their specific genetic determination and in particular, the specific genes that may regulate the circulating concentrations of these substances. In the present study, we examined whether nine single nucleotide polymorphisms (SNPs) in the human homologue of the mouse progressive ankylosis gene (ANKH)-one of the key genetic factors involved in bone mineralization-can be associated with PTH and BGP levels in apparently healthy human populations. The study sample comprised 244 nuclear families (840 individuals). After adjustment of BGP and PTH for the significant covariates (sex, age and BMI), the contribution of the putative genetic effects was statistically significant (P < 0.001) for both biochemical factors: 45.27 +/- 10.8% for PTH and 30.19 +/- 12.6% for BGP. Application of transmission disequilibrium tests (TDTs) revealed a significant association (P < 0.05) between PTH and two SNPs: rs39968 and rs875525. However, the association became particularly significant for four TDTs (P-values ranging from 0.0025 to 0.0008) when the association with the haplotypes generated from the above SNP was tested. This association remained significant even after correction for multiple testing with a false discovery rate of 0.05.

Genetics and experimental models of crystal-induced arthritis. Lessons learned from mice and men: is it crystal clear?

PURPOSE OF REVIEW

We examine the major genes in mice and humans involved in the pathogenesis of monosodium urate, calcium pyrophosphate dihydrate and hydroxyapatite crystal-induced arthritis.

RECENT FINDINGS

Several genetic causes of renal disease associated with hyperuricemia and gout provide insight into genes involved in renal urate handling. Mutations or polymorphisms in exons 4 and 5 and intron 4 of urate transporter 1 may be independent genetic markers of hyperuricemia and gout. Genetic analysis supports the role of ANKH mutations in calcium pyrophosphate dihydrate-induced arthritis. ANKH gain-of-function mutations were confirmed by functional studies; however, the crystals formed in ATD5 cells were basic calcium phosphate, not calcium pyrophosphate dihydrate, underlying the significance of chondrocyte differentiation state and the factors regulating normal and pathological mineralization. Animal models have implicated a general model of crystal-induced inflammation involving innate immunity through the NALP3 (Natch domain, leucine-rich repeat, and PYD-containing protein 3) inflammasome signaling through the interleukin-1 receptor and its signaling protein myeloid differentiation primary response protein 88.

SUMMARY

Genetic analysis has elucidated genes responsible for crystal formation and animal models have unveiled mechanisms in the development of crystal-induced arthritis. Future studies will hasten understanding of the pathology of crystal-induced arthritis and provide new therapies.

Association of a TNAP haplotype with ankylosing spondylitis

OBJECTIVE

To use a candidate gene approach to the identification of genetic markers that are significantly associated with ankylosing spondylitis (AS).

METHODS

We genotyped 201 multiplex AS families with 1 exonic and 5 intronic single-nucleotide polymorphisms (SNPs) in TNAP, the gene that encodes tissue-nonspecific alkaline phosphatase, and performed family-based association analyses.

RESULTS

In our cohort of 201 multiplex AS families, the TNAP haplotype rs3767155 (G)/rs3738099 (G)/rs1780329 (T) was significantly associated with AS (P = 0.032 by additive model). Haplotype-Based Association Testing (HBAT) analyses of AS families in which both men and women were affected showed that the same TNAP haplotype was significantly associated with AS (P = 0.002 by additive model). Using setafftrait code 1 0 0 in the HBAT program, testing specifically for affected men in AS families containing affected individuals of both sexes, this TNAP haplotype was also significantly associated with AS (P = 0.001 by additive model). The HBAT -p option (haplotype permutation test) was used to compute the "exact" P value via a Monte Carlo method for each haplotype (haplotype permutation test) and for the minimum observed P value among the haplotypes (whole marker permutation using the minimal P test), and both P values were statistically significant (2-sided P value for haplotype rs3767155 [G]/rs3738099 [G]/rs1780329 [T] = 0.00059, the smallest observed P value among all the individual haplotype scores = 0.003). Interestingly, this haplotype was not associated with AS in affected women from the same families.

CONCLUSION

Our results indicate that the TNAP haplotype rs3767155 (G)/rs3738099 (G)/rs1780329 (T) is a novel genetic marker in men that is significantly associated with AS in multiplex families containing affected individuals of both sexes.

Spondyloarthropathy: an independent risk factor for kidney stones

PURPOSE

To better stratify risk and to verify previous prevalence reports, we conducted a retrospective cohort study comparing the lifetime incidence of nephrolithiasis in patients with spondyloarthropathies (SpA) and rheumatoid arthritis (RA).

PATIENTS AND METHODS

Patients with SpA or rheumatoid factor-positive RA were identified from the rheumatology clinics of two Veterans Affairs hospitals and the University of Minnesota. Among them, 168 were confirmed to meet the American College of Rheumatology criteria and gave informed consent to participation. They were sent a survey regarding their rheumatologic diagnosis, coexistent conditions, medications, and history of kidney stones. Of the total, 143 patients responded and met the criteria for analysis. Rheumatoid arthritis patients were age and sex matched with SpA patients as controls.

RESULTS

Populations were similar in all categories except that RA patients were more likely to have used prednisone (P < 0.001), bisphosphonates (P < 0.001), and calcium supplementation (P = 0.03). Kidney stones were reported by 23 (29.11%) of the 79 SpA patients compared with 8 (12.5%) of the 64 RA patients (chi (2) = 5.75; P = 0.025). Subgroup analysis of self-reporting stone history in 85 patients was found to be reliable on imaging review (sensitivity 82%; specificity 100%).

CONCLUSIONS

Self-reporting of kidney stones by patients is a reliable measure. Despite adjusting for medication use and matching two similar arthritic populations, patients with SpA had a higher incidence of kidney stones than those with RA. This finding suggests that SpA is an independent risk factor for nephrolithiasis. Future studies will evaluate urinary risk factors and polymorphisms in the ANKH gene that may predispose to stone formation in this high-risk group.

Biochemical and genetic analysis of ANK in arthritis and bone disease

Mutations in the progressive ankylosis gene (Ank/ANKH) cause surprisingly different skeletal phenotypes in mice and humans. In mice, recessive loss-of-function mutations cause arthritis, ectopic crystal formation, and joint fusion throughout the body. In humans, some dominant mutations cause chondrocalcinosis, an adult-onset disease characterized by the deposition of ectopic joint crystals. Other dominant mutations cause craniometaphyseal dysplasia, a childhood disease characterized by sclerosis of the skull and abnormal modeling of the long bones, with little or no joint pathology. Ank encodes a multiple-pass transmembrane protein that regulates pyrophosphate levels inside and outside tissue culture cells in vitro, but its mechanism of action is not yet clear, and conflicting models have been proposed to explain the effects of the human mutations. Here, we test wild-type and mutant forms of ANK for radiolabeled pyrophosphate-transport activity in frog oocytes. We also reconstruct two human mutations in a bacterial artificial chromosome and test them in transgenic mice for rescue of the Ank null phenotype and for induction of new skeletal phenotypes. Wild-type ANK stimulates saturable transport of pyrophosphate ions across the plasma membrane, with half maximal rates attained at physiological levels of pyrophosphate. Chondrocalcinosis mutations retain apparently wild-type transport activity and can rescue the joint-fusion phenotype of Ank null mice. Craniometaphyseal dysplasia mutations do not transport pyrophosphate and cannot rescue the defects of Ank null mice. Furthermore, microcomputed tomography revealed previously unappreciated phenotypes in Ank null mice that are reminiscent of craniometaphyseal dysplasia. The combination of biochemical and genetic analyses presented here provides insight into how mutations in ANKH cause human skeletal disease.

Are there gender differences in severity of ankylosing spondylitis? Results from the PSOAS cohort

OBJECTIVE

To examine the clinical and radiographic features in men and women in the Prospective Study of Outcomes in Ankylosing Spondylitis cohort, a large well-defined cross-sectional study of patients with AS, in order to understand the influence of gender in determining the severity of ankylosing spondylitis.

METHODS

Extensive clinical assessments and spine radiographs were performed in 302 men and 100 women with AS of > or = 20 years duration. Radiographs were scored using the Bath Ankylosing Spondylitis Radiographic Index Spine (BASRI-spine) score (range 2-12). Functional impairment was measured by the Bath Ankylosing Spondylitis Functional Index (BASFI) and the Health Assessment Questionnaire for the Spondyloarthropathies (HAQ-S).

RESULTS

Radiographic severity was worse among men. The unadjusted median BASRI-spine score for men was 10, compared with 6.5 for women (p<0.001). Functional disability, as measured by the BASFI and HAQ-S, was not different between men and women. However, after adjusting for radiographic spinal damage, women were found to report worse functioning than men at any given level of radiographic damage. Women had a slightly earlier age of disease onset; however, disease duration was identical in both groups. Women more frequently reported family histories of AS in first-degree relatives and were more likely to be treated with intra-articular steroids, sulphasalazine and prednisone.

CONCLUSIONS

Among patients with longstanding AS, men have more severe radiographic changes; findings of treatment differences suggest that women may have more peripheral arthritis. At any given level of radiographic damage, self-reported functional limitations were worse for women.

Mineral formation in joints caused by complete or joint-specific loss of ANK function

To reveal the ANK complete loss of function phenotype in mice, we generated conditional and null alleles. Mice homozygous for the null allele exhibited widespread joint mineralization, similar in severity to animals harboring the original ank allele. A delayed yet similar phenotype was observed in mice with joint-specific loss of ANK function.

INTRODUCTION

The ANK pyrophosphate regulator was originally identified and proposed to play a key role in articular cartilage maintenance based on a single spontaneous mouse mutation (ank) that causes severe generalized arthritis. A number of human mutations have subsequently been reported in the human ortholog (ANKH), some of which produce skull and long bone defects with no apparent defects in joints or articular cartilage. None of the currently known mouse or human mutations clearly eliminate the function of the endogenous gene.

MATERIALS AND METHODS

Two new Ank alleles were generated using homologous recombination in mouse embryonic stem (ES) cells. Joint range of motion assays and muCT studies were used to quantitatively assess phenotypic severity in wildtype, heterozygous, and homozygous mice carrying either the null (Anknull) or original (Ankank) allele. A Gdf5-Cre expressing line was crossed to mice harboring the conditional (Ankfloxp) allele to eliminate ANK function specifically in the joints. Histological stains and beta-galactosidase (LACZ) activity were used to determine the correlation between local loss of ANK function and defective joint phenotypes.

RESULTS

Anknull/Anknull mice develop severe ectopic postnatal crystal deposition in almost every joint of the body, leading to eventual joint fusion and loss of mobility. The severity of phenotype in these mice is indistinguishable from that of Ankank/Ankank mice. In addition, despite the widespread expression of Ank in many tissues, the specific deletion of Ank in joints also produces joint mineralization and ankylosis.

CONCLUSIONS

These studies show that ANK function is required locally in joints to inhibit mineral formation and that the Ank gene plays a key role in postnatal maintenance of joint mobility and function.