The genetic contribution to longitudinal changes in knee structure and muscle strength: A sibpair study

Changes in Circulating MicroRNA Levels as Potential Indicators of Training Adaptation in Professional Volleyball Players

The increasing demand placed on professional athletes to enhance their fitness and performance has prompted the search for new, more sensitive biomarkers of physiological ability. One such potential biomarker includes microRNA (miRNA) small regulatory RNA sequences. The study investigated the levels of the selected circulating miRNAs before and after a 10-week training cycle in 12 professional female volleyball players, as well as their association with cortisol, creatine kinase (CK), and interleukin 6 (IL-6), using the qPCR technique. Significant decreases in the miR-22 (0.40 ± 0.1 vs. 0.28 ± 0.12, p = 0.009), miR-17 (0.35 ± 0.13 vs. 0.23 ± 0.08; p = 0.039), miR-24 (0.09 ± 0.04 vs. 0.05 ± 0.02; p = 0.001), and miR-26a (0.11 ± 0.06 vs. 0.06 ± 0.04; p = 0.003) levels were observed after training, alongside reduced levels of cortisol and IL-6. The correlation analysis revealed associations between the miRNAs' relative quantity and the CK concentrations, highlighting their potential role in the muscle repair processes. The linear regression analysis indicated that miR-24 and miR-26a had the greatest impact on the CK levels. The study provides insights into the dynamic changes in the miRNA levels during training, suggesting their potential as biomarkers for monitoring the adaptive responses to exercise. Overall, the findings contribute to a better understanding of the physiological effects of exercise and the potential use of miRNAs, especially miR-24 and miR-26a, as biomarkers in sports science and medicine.

Restoration of epigenetic impairment in the skeletal muscle and chronic inflammation resolution as a therapeutic approach in sarcopenia

Sarcopenia is an age-associated loss of skeletal muscle mass, strength, and function, accompanied by severe adverse health outcomes, such as falls and fractures, functional decline, high health costs, and mortality. Hence, its prevention and treatment have become increasingly urgent. However, despite the wide prevalence and extensive research on sarcopenia, no FDA-approved disease-modifying drugs exist. This is probably due to a poor understanding of the mechanisms underlying its pathophysiology. Recent evidence demonstrate that sarcopenia development is characterized by two key elements: (i) epigenetic dysregulation of multiple molecular pathways associated with sarcopenia pathogenesis, such as protein remodeling, insulin resistance, mitochondria impairments, and (ii) the creation of a systemic, chronic, low-grade inflammation (SCLGI). In this review, we focus on the epigenetic regulators that have been implicated in skeletal muscle deterioration, their individual roles, and possible crosstalk. We also discuss epidrugs, which are the pharmaceuticals with the potential to restore the epigenetic mechanisms deregulated in sarcopenia. In addition, we discuss the mechanisms underlying failed SCLGI resolution in sarcopenia and the potential application of pro-resolving molecules, comprising specialized pro-resolving mediators (SPMs) and their stable mimetics and receptor agonists. These compounds, as well as epidrugs, reveal beneficial effects in preclinical studies related to sarcopenia. Based on these encouraging observations, we propose the combination of epidrugs with SCLI-resolving agents as a new therapeutic approach for sarcopenia that can effectively attenuate of its manifestations.

Pathophysiology of sarcopenia: Genetic factors and their interplay with environmental factors

Sarcopenia is a geriatric disorder characterized by a progressive decline in muscle mass and function. This disorder has been associated with a range of adverse health outcomes, including fractures, functional deterioration, and increased mortality. The pathophysiology of sarcopenia is highly complex and multifactorial, involving both genetic and environmental factors as key contributors. This review consolidates current knowledge on the genetic factors influencing the pathogenesis of sarcopenia, particularly focusing on the altered gene expression of structural and metabolic proteins, growth factors, hormones, and inflammatory cytokines. While the influence of environmental factors such as physical inactivity, chronic diseases, smoking, alcohol consumption, and sleep disturbances on sarcopenia is relatively well understood, there is a dearth of studies examining their mechanistic roles. Therefore, this review emphasizes the interplay between genetic and environmental factors, elucidating their cumulative role in exacerbating the progression of sarcopenia beyond their individual effects. The unique contribution of this review lies in synthesizing the latest evidence on the genetic factors and their interaction with environmental factors, aiming to inform the development of novel therapeutic or preventive interventions for sarcopenia.

The Genetic Association with Athlete Status, Physical Performance, and Injury Risk in Soccer

The aim of this review was to critically appraise the literature concerning the genetic association with athlete status, physical performance, and injury risk in soccer. The objectives were to provide guidance on which genetic markers could potentially be used as part of future practice in soccer and to provide direction for future research in this area. The most compelling evidence identified six genetic polymorphisms to be associated with soccer athlete status (ACE I/D; ACTN3 rs1815739; AGT rs699; MCT1 rs1049434; NOS3 rs2070744; PPARA rs4253778), six with physical performance (ACTN3 rs1815739; AMPD1 rs17602729; BDNF rs6265; COL2A1 rs2070739; COL5A1 rs12722; NOS3 rs2070744), and seven with injury risk (ACTN3 rs1815739; CCL2 rs2857656; COL1A1 rs1800012; COL5A1 rs12722; EMILIN1 rs2289360; IL6 rs1800795; MMP3 rs679620). As well as replication by independent groups, large-scale genome-wide association studies are required to identify new genetic markers. Future research should also investigate the physiological mechanisms associating these polymorphisms with specific phenotypes. Further, researchers should investigate the above associations in female and non-Caucasian soccer players, as almost all published studies have recruited male participants of European ancestry. Only after robust, independently replicated genetic data have been generated, can genetic testing be considered an additional tool to potentially inform future practice in soccer.

Epigenetic Analysis of the Dopamine Transporter Gene DAT1 with a Focus on Personality Traits in Athletes

Human phenotypes (traits) are determined by the selective use of a person's unique genotype (DNA sequence), following exposure to environmental stimuli, such as exercise. Inducing profound changes in epigenetics may be an underlying factor of the beneficial effects of exercise. This study aimed to investigate the association between methylation in the promoter region of the DAT1 gene and personality traits measured by the NEO-FFI questionnaire in a group of athletes. The study group included 163 athletes, and the control group consisted of 232 non-athletes. The obtained results show several significant differences between the studied groups of subjects. The Extraversion scale and the Conscientiousness scale results of the NEO-FFI are significantly higher in the group of athletes compared to controls. The total methylation and the number of methylated islands in the promoter region of the DAT1 gene are higher in the study group. Pearson's linear correlation between the total methylation, the number of methylated islands and the NEO-FFI shows significant results for the Extraversion and Agreeability scales. The total methylation and the number of methylated islands in the promoter region of the DAT1 gene are higher in the study group. Pearson's linear correlation between the total methylation, the number of methylated islands and the NEO-FFI shows significant results for the Extraversion and Agreeability scales. Our analysis of the methylation status of individual CpG sites revealed a new direction of research into the biological aspects of regulating dopamine release and personality traits in people practicing sports.

Identification of LRRK2 gene related to sarcopenia and neuroticism using weighted gene co-expression network analysis

BACKGROUND

Sarcopenia is reported to be associated with neuroticism, but the mechanisms are not fully understood. Thus, it's of vital importance to elucidate the molecular mechanism of sarcopenia and neuroticism and to explore the potential molecular target of medical therapies for sarcopenia and neuroticism.

METHODS

The expression datasets (sarcopenia: GSE111006 and neuroticism: GSE60491) were downloaded from the Gene Expression Omnibus. Weighted gene co-expression network analysis (WGCNA) was used to build the gene co-expression network, screen important modules, and filter the hub genes. Genes with significance over 0.2 and a module membership over 0.8 were hub genes. The overlapped hub genes between sarcopenia and neuroticism were defined as key genes. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses were performed for the genes in modules with clinical interest.

RESULTS

In this study, we identified 28 gene modules for sarcopenia and 7 for neuroticism by WGCNA. The key modules of sarcopenia and neuroticism were the tan and turquoise modules, respectively. Hub genes of sarcopenia and neuroticism were 20 genes and 107 genes, respectively. The function enrichment found that apoptosis was the common pathway for sarcopenia and neuroticism. Finally, LRRK2 was identified as key genes.

LIMITATIONS

The sarcopenia dataset contained fewer samples.

CONCLUSION

Based on WGCNA, our study identified apoptosis pathway and LRRK2 that acted as essential components in the etiology of sarcopenia and neuroticism, which may enhance our fundamental knowledge of the molecular mechanisms underlying the disease.

Extracellular vesicles in osteoarthritis of peripheral joint and temporomandibular joint

Osteoarthritis (OA) is a disabling disease with significant morbidity worldwide. OA attacks the large synovial joint, including the peripheral joints and temporomandibular joint (TMJ). As a representative of peripheral joint OA, knee OA shares similar symptoms with TMJ OA. However, these two joints also display differences based on their distinct development, anatomy, and physiology. Extracellular vesicles (EVs) are phospholipid bilayer nanoparticles, including exosomes, microvesicles, and apoptotic bodies. EVs contain proteins, lipids, DNA, micro-RNA, and mRNA that regulate tissue homeostasis and cell-to-cell communication, which play an essential role in the progression and treatment of OA. They are likely to partake in mechanical response, extracellular matrix degradation, and inflammatory regulation during OA. More evidence has shown that synovial fluid and synovium-derived EVs may serve as OA biomarkers. More importantly, mesenchymal stem cell-derived EV shows a therapeutic effect on OA. However, the different function of EVs in these two joints is largely unknown based on their distinct biological characteristic. Here, we reviewed the effects of EVs in OA progression and compared the difference between the knee joint and TMJ, and summarized their potential therapeutic role in the treatment of OA.

A Genome-Wide Association Study Identifies Novel Risk Loci for Sarcopenia in a Taiwanese Population

Purpose

A genome-wide association study (GWAS) of sarcopenia unraveled the importance of genetic contribution to decline in muscle. The current study investigated sarcopenia-related single nucleotide polymorphisms (SNPs) in Asian older adults, and further constructed a genotype score that tests the combined effect of these SNPs on risk of sarcopenia.

Patients and Methods

Ninety-six subjects aged 60 or above were recruited from the database of annual geriatric health examination at Tri-Service General Hospital during 2020. Eligible criteria included: 1) not having severe comorbidities; 2) agreed to join the Taiwan Precision Medicine Initiative project; and 3) having sufficient information of required sarcopenic measurements. Genotype–phenotype association analysis was performed to find SNPs that were significantly associated with each of three sarcopenic indices (low muscle mass, muscle strength, and physical performance). Subsequently, these SNPs comprised a sarcopenia-related genotype score that summed up the number of SNPs carrying unfavorable allele(s).

Results

Twelve SNPs revealed suggestive genome-wide significance with the three sarcopenic indices, and eight of them revealed a relationship with more than one index. Low muscle strength was the item that had the most (eight) related SNPs. Among them, rs10282247 affects cholesterol binding and rs7022373 participates in cellular apoptosis. In addition, higher genotype score demonstrated higher risk of sarcopenia (≥4 points: OR=630.6; 2–3 points: OR=408, p-value<0.001).

Conclusion

Several newly discovered SNPs suggest that genetic contribution plays a part in the pathogenesis of sarcopenia. Further studies are warranted to verify the underlying mechanisms. Moreover, a genotype score provides an estimate of the combined effect of genetic association with sarcopenia, which may modestly improve clinical risk classification.

Pilot Study on Genetic Associations With Age-Related Sarcopenia

Despite strong evidence of an inheritable component of muscle phenotypes, little progress has been made in identifying the specific genetic factors involved in the development of sarcopenia. Even rarer are studies that focus on predicting the risk of sarcopenia based on a genetic risk score. In the present study, we tested the single and combined effect of seven candidate gene variants on the risk of sarcopenia. Single nucleotide polymorphisms in candidate genes were genotyped using the KASP assay. We examined 190 older adults that were classified as non-sarcopenic or sarcopenic according to the diagnostic criteria of the European Working Group on Sarcopenia in Older People. Sarcopenia was associated with Methylenetetrahydrofolate reductase, Alpha-actinin-3, and Nuclear respiratory factor 2 genotypes. The combined effect of all three polymorphisms explained 39% of the interindividual variation in sarcopenia risk. Our results suggest that the single and combined effect of Methylenetetrahydrofolate reductase, Alpha-actinin-3, and Nuclear respiratory factor 2 polymorphism is associated with sarcopenia risk in older adults. Nowadays, as the population is getting older and older, great efforts are being made to research the etiology, diagnosis and treatment of sarcopenia. At the same time, small progress has been made in understanding the genetic etiology of sarcopenia. Given the importance of research on this disease, further genetic studies are needed to better understand the genetic risk underlying sarcopenia. We believe that this small-scale study will help to demonstrate that there is still much to be discovered in this field.

Arthritis and the role of endogenous glucocorticoids

Rheumatoid arthritis and osteoarthritis, the most common forms of arthritis, are chronic, painful, and disabling conditions. Although both diseases differ in etiology, they manifest in progressive joint destruction characterized by pathological changes in the articular cartilage, bone, and synovium. While the potent anti-inflammatory properties of therapeutic (i.e., exogenous) glucocorticoids have been heavily researched and are widely used in clinical practice, the role of endogenous glucocorticoids in arthritis susceptibility and disease progression remains poorly understood. Current evidence from mouse models suggests that local endogenous glucocorticoid signaling is upregulated by the pro-inflammatory microenvironment in rheumatoid arthritis and by aging-related mechanisms in osteoarthritis. Furthermore, these models indicate that endogenous glucocorticoid signaling in macrophages, mast cells, and chondrocytes has anti-inflammatory effects, while signaling in fibroblast-like synoviocytes, myocytes, osteoblasts, and osteocytes has pro-inflammatory actions in rheumatoid arthritis. Conversely, in osteoarthritis, endogenous glucocorticoid signaling in both osteoblasts and chondrocytes has destructive actions. Together these studies provide insights into the role of endogenous glucocorticoids in the pathogenesis of both inflammatory and degenerative joint disease.

The Prospective Study of Epigenetic Regulatory Profiles in Sport and Exercise Monitored Through Chromosome Conformation Signatures

The integration of genetic and environmental factors that regulate the gene expression patterns associated with exercise adaptation is mediated by epigenetic mechanisms. The organisation of the human genome within three-dimensional space, known as chromosome conformation, has recently been shown as a dynamic epigenetic regulator of gene expression, facilitating the interaction of distal genomic regions due to tight and regulated packaging of chromosomes in the cell nucleus. Technological advances in the study of chromosome conformation mean a new class of biomarker-the chromosome conformation signature (CCS)-can identify chromosomal interactions across several genomic loci as a collective marker of an epigenomic state. Investigative use of CCSs in biological and medical research shows promise in identifying the likelihood that a disease state is present or absent, as well as an ability to prospectively stratify individuals according to their likely response to medical intervention. The association of CCSs with gene expression patterns suggests that there are likely to be CCSs that respond, or regulate the response, to exercise and related stimuli. The present review provides a contextual background to CCS research and a theoretical framework discussing the potential uses of this novel epigenomic biomarker within sport and exercise science and medicine.

Clinical relevance of biochemical and metabolic changes in osteoarthritis

Osteoarthritis (OA) is a multifactorial disease with huge phenotypic heterogeneity. The disease affects all tissues in the joint, and the loss of articular cartilage is its hallmark. The main biochemical components of the articular cartilage are type II collagen, aggrecan, and water. Transforming growth factor-beta (TGF-β) signaling is one of the signaling pathways that maintains the healthy cartilage. However, the two subpathways of the TGF-β signaling-TGF-β and bone morphogenetic proteins (BMP) subpathways, lose their balance in OA, resulting an increased expression of cartilage degradation enzymes including matrix metallopeptidase 13 (MMP13), cathepsin B (CTSB), and cathepsin K (CTSK) and a decreased expression of aggrecan (ACAN). Thus, restoring the balance of two subpathways might provide a new avenue for treating OA patients. Further, metabolic changes are seen in OA and can be used to distinguish different subtypes of OA patients. Metabolomics studies showed that at least three endotypes of OA can be distinguished: 11% of OA patients are characterized by an elevated blood butyryl carnitine, 33% of OA patients have significant reduced arginine concentration, and 56% with metabolic alteration in phospholipid metabolism. While these findings need to be confirmed, they are promising personalized medicine tools for OA management.

Genetic Associations with Aging Muscle: A Systematic Review

The age-related decline in skeletal muscle mass, strength and function known as 'sarcopenia' is associated with multiple adverse health outcomes, including cardiovascular disease, stroke, functional disability and mortality. While skeletal muscle properties are known to be highly heritable, evidence regarding the specific genes underpinning this heritability is currently inconclusive. This review aimed to identify genetic variants known to be associated with muscle phenotypes relevant to sarcopenia. PubMed, Embase and Web of Science were systematically searched (from January 2004 to March 2019) using pre-defined search terms such as "aging", "sarcopenia", "skeletal muscle", "muscle strength" and "genetic association". Candidate gene association studies and genome wide association studies that examined the genetic association with muscle phenotypes in non-institutionalised adults aged ≥50 years were included. Fifty-four studies were included in the final analysis. Twenty-six genes and 88 DNA polymorphisms were analysed across the 54 studies. The ACTN3, ACE and VDR genes were the most frequently studied, although the IGF1/IGFBP3, TNFα, APOE, CNTF/R and UCP2/3 genes were also shown to be significantly associated with muscle phenotypes in two or more studies. Ten DNA polymorphisms (rs154410, rs2228570, rs1800169, rs3093059, rs1800629, rs1815739, rs1799752, rs7412, rs429358 and 192 bp allele) were significantly associated with muscle phenotypes in two or more studies. Through the identification of key gene variants, this review furthers the elucidation of genetic associations with muscle phenotypes associated with sarcopenia.

Bone shape mediates the relationship between sex and incident knee osteoarthritis

Background

Knee bone shape differs between men and women and the incidence of knee osteoarthritis (OA) is higher in women than in men. Therefore, the purpose of the present study was to determine whether the observed difference in the incidence of knee radiographic OA (ROA) between men and women is mediated by bone shape.

Methods

We randomly sampled 304 knees from the OAI with incident ROA (i.e., development of Kellgren/Lawrence grade ≥ 2 by month 48) and 304 knees without incident ROA. We characterized distal femur and proximal tibia shape on baseline radiographs using Statistical Shape Modeling. If a specific bone shape was associated with the risk of incident ROA, marginal structural models were generated to assess the mediation effect of that bone shape on the relation of sex and risk of incident knee ROA adjusting for baseline covariates.

Results

Case and control participants were similar by age, sex and race, but case knees were from higher body mass index (BMI) participants (29.4 vs. 27.0; p < 0.001). Women had 49% increased odds of incident knee ROA compared with men (adjusted odds ratio (OR) = 1.49, 95% Confidence Interval (C.I.): 1.04, 2.12). There was an inconsistent mediation effect for tibial mode 2 between sex and incident knee ROA, with an indirect effect OR of 0.96 (95% C.I.: 0.91–1.00) and a direct effect OR of 1.56 (95% C.I.: 1.08–2.27), suggesting a protective effect for this mode. Similar findings were also observed for the mediation effect of tibia mode 10 and femur mode 4. These shape modes primarily involved differences in the angular relation of the heads to the shafts of the femur and tibia.

Conclusions

Distal femur and proximal tibia bone shapes partially and inconsistently mediated the relationship between sex and incident knee OA. Women had a higher risk of incident ROA, and specific bone shapes modestly protected them from even higher risk of ROA. The clinical significance of these findings warrant further investigation.

Familial effects on structural changes relevant to knee osteoarthritis: a prospective cohort study

OBJECTIVE

Genetic factors play an important role in the pathogenesis of knee osteoarthritis (OA), but which knee structural changes mediate this is unclear. This study aimed to describe the differences in knee structural changes over 8-10 years between offspring having at least one parent with total knee replacement (TKR) for severe primary knee OA and controls with no family history of knee OA.

DESIGN

115 offspring (mean age 45 years) with a family history of TKR for severe knee OA were compared with 104 (mean age 46 years) controls. T1 or T2-weighted fat saturated magnetic resonance imaging (MRI) was performed respectively to evaluate knee cartilage defects, bone marrow lesions (BMLs), meniscal extrusion and tears at baseline and 10 years. Multivariate logistic regression model was used to adjust for potential confounders.

RESULTS

Offspring had a greater increase in cartilage defect score (1.03 vs 0.52, P = 0.007) and meniscal extrusion score (0.28 vs 0.10, P = 0.027) over 10 years, and a greater increase in meniscal tear score (0.40 vs 0.10, P = 0.012) over 8 years in the medial but not the lateral tibiofemoral compartment. Changes in BMLs over 8-years were not different between the two groups. These associations were independent of potential confounders, and strengthened after further adjustment for each other.

CONCLUSION

With the exception of BMLs, offspring with a family history of knee OA have a greater risk of increases in multiple knee structural abnormalities in the medial tibiofemoral compartment suggesting pleiotropic familial effects.

A family history of knee joint replacement increases the progression of knee radiographic osteoarthritis and medial tibial cartilage volume loss over 10 years

OBJECTIVES

Osteoarthritis (OA) has a genetic component but it is uncertain if the offspring of those with knee OA are at a greater risk. The aim of this study was to describe radiographic OA (ROA) progression and cartilage loss over 10 years in a midlife cohort with some having a family history of OA and some community based controls.

METHODS

220 participants [mean-age 45 (26-61); 57% female] were studied at baseline and 10 years. Half were adult offspring of subjects who underwent knee replacement for OA and the remainder were randomly selected controls. Joint space narrowing (JSN) and osteophytes were assessed on radiographs and cartilage volume (tibial, femoral and patellar), cartilage defects, bone marrow lesions (BMLs) and meniscal tears were assessed on Magnetic resonance imaging (MRI).

RESULTS

For ROA, there was a significant difference between offspring and controls in unadjusted analysis for change in total ROA, medial JSN, total medial, total lateral and total osteophyte scores. This difference persisted for medial JSN (difference in ratios = +1.93 (+1.04, +3.51)) only, after adjustment for confounders and baseline differences. In unadjusted analysis for cartilage loss, offspring lost more cartilage at the medial tibial (difference in means = -79.13 (-161.92, +3.71)) site only. This difference became of borderline significance after adjustment for baseline differences (P = 0.055).

CONCLUSION

The offspring of subjects having a total knee replacement have a greater worsening of ROA (both JSN and osteophytes) and higher medial tibial cartilage volume loss over 10 years. Most of these changes are mediated by differences in baseline characteristics of offspring and controls except for increase in medial JSN.

Motor neuropathy

In distal symmetric sensorimotor polyneuropathy (DSPN) in diabetes, involvement of the motor system is rarely seen. Using dynamometry, substantial weakness at the ankle and knee has been found in type 1 and type 2 diabetic patients. The muscle weakness is found only in diabetic patients with DSPN, and is closely related to signs and severity of DSPN. In long-term follow-up studies, neuropathic patients have accelerated loss of muscle strength. Studies using MRI have shown that muscle weakness is paralleled by muscular atrophy within the feet and lower legs and in follow-up studies this atrophy is accelerated compared to healthy controls and non-neuropathic patients. In large-scale studies of diabetic subjects, lower muscle quality has been found, which indicates that even with preserved muscle strength diabetes per se causes lower strength per unit striated muscle. Muscle weakness causes slower movements of the feet and legs, unstable gait, and more frequent falls. Furthermore, weakness is also an independent risk factor for the development of foot ulcers. Training may improve strength, postural stability, and walking performance; however, this still needs to be studied including patients with various degrees of DSPN.

Genetic factors in OA pathogenesis

Osteoarthritis (OA) is known to have an important genetic component and human genetic studies can help unravel the molecular mechanisms responsible for joint damage and nociception involved in OA. Genetic studies in humans have identified molecules involved in signaling cascades that are important for the pathology of the joint components such as the bone morphogenetic protein growth differentiation factor 5 (GDF5). Genomewide association scans (GWAS) in Asians have uncovered a likely role for structural extracellular matrix components (DVWA), and for molecules involved in immune response (HLA class II DQB1 and BTNL2) but these genes are not associated in Caucasian patients. In Caucasians a ~300 kilobase region in chromosome 7q22 containing several genes has been found to be reproducibly associated with OA. A recent European GWAS taking advantage of imputation techniques has uncovered a variant in the MCF2L gene as significantly associated with large joint OA. MCF2L is involved in neurotrophin mediated regulation of cell motility in the peripheral nervous system, and thus potentially implicated in nociception in OA. As the number of OA cases with genomewide genotyping increases it is expected that many more reproducible variants implicated in OA will be reported. This article is part of a Special Issue entitled "Osteoarthritis".

Genetic aspects of skeletal muscle strength and mass with relevance to sarcopenia

Skeletal muscle is a highly heritable quantitative trait, with heritability estimates ranging 30-85% for muscle strength and 50-80% for lean mass. That strong genetic contribution indicates the possibility of using genetic information to individualize treatments for sarcopenia or even aid in prevention strategies through the use of genetic screening prior to the functional limitations. Though these possibilities provide the rationale for genetic studies of skeletal muscle traits, few genes have been identified that appear to contribute to variation in either skeletal muscle strength or mass phenotypes, and sarcopenia per se is remarkably understudied as a trait in this regard. This review examines the heritability of skeletal muscle traits, findings of linkage and genome-wide association analyses and impact of specific genes and gene-sequence variants on these traits as relevant to sarcopenia. Despite considerable work in the area, the genetic underpinnings of skeletal muscle traits remain largely unknown and the genetic aspects of sarcopenia are even less clear. Large-scale longitudinal clinical studies relying on advanced genome-wide association and other techniques are needed to provide further insights into the genes and gene variants that contribute to skeletal muscle strength and mass, and ultimately to susceptibility to sarcopenia.

The epidemiology of sarcopenia in community living older adults: what role does lifestyle play?

BACKGROUND: Sarcopenia, the age-related decline in skeletal muscle mass and function, is a relatively poorly understood process which may play an important role in the incidence of physical disability and falls in older adults. Evidence demonstrates that both genetic and environmental factors contribute to increased susceptibility for sarcopenia development, yet some of these factors may represent unavoidable consequences of ageing. METHODS: A review of literature, generally from epidemiological research, was performed to examine the influence that potentially modifiable lifestyle factors (general physical activity, dietary nutrient intake and sun exposure), as well as chronic disease and medication use, may have on sarcopenia progression. RESULTS: The review demonstrated that while physical activity, nutrient intake and sun exposure often decline during ageing, each may have important but differing benefits for the prevention of muscle mass and functional declines in older adults. Conversely, age-related increases in the prevalence of chronic diseases and the subsequent prescription of pharmacotherapy may exacerbate sarcopenia progression. CONCLUSIONS: The prevalence of poor physical activity, diet and sun exposure, as well as chronic disease and medication use, within older adult populations may be modifiable through simple lifestyle and health care interventions. As such, these factors may represent the most effective targets for sarcopenia prevention during the ageing process.

Molecular genetic studies of gene identification for sarcopenia

Sarcopenia, which is characterized by a progressive decrease of skeletal muscle mass and function with aging, is closely related to several common diseases (such as cardiovascular and airway diseases) and functional impairment/disability. Strong genetic determination has been reported for muscle mass and muscle strength, two most commonly recognized and studied risk phenotypes for sarcopenia, with heritability ranging from 30 to 85% for muscle strength and 45-90% for muscle mass. Sarcopenia has been the subject of increasing genetic research over the past decade. This review is designed to comprehensively summarize the most important and representative molecular genetic studies designed to identify genetic factors associated with sarcopenia. We have methodically reviewed whole-genome linkage studies in humans, quantitative trait loci mapping in animal models, candidate gene association studies, newly reported genome-wide association studies, DNA microarrays and microRNA studies of sarcopenia or related skeletal muscle phenotypes. The major results of each study are tabulated for easy comparison and reference. The findings of representative studies are discussed with respect to their influence on our present understanding of the genetics of sarcopenia. This is a comprehensive review of molecular genetic studies of gene identification for sarcopenia, and an overarching theme for this review is that the currently accumulating results are tentative and occasionally inconsistent and should be interpreted with caution pending further investigation. Consequently, this overview should enhance recognition of the need to validate/replicate the genetic variants underlying sarcopenia in large human cohorts and animal. We believe that further progress in understanding the genetic etiology of sarcopenia will provide valuable insights into important fundamental biological mechanisms underlying muscle physiology that will ultimately lead to improved ability to recognize individuals at risk for developing sarcopenia and our ability to treat this debilitating condition.

Genetic epidemiology of hip and knee osteoarthritis

Osteoarthritis (OA) is the most common cause of arthritis and represents an enormous healthcare burden in industrialized societies. Current therapeutic approaches for OA are limited and are insufficient to prevent the initiation and progression of the disease. Genetic studies of patients with OA can help to unravel the molecular mechanisms responsible for specific disease manifestations, including joint damage, nociception and chronic pain. Indeed, these studies have identified molecules, such as growth/differentiation factor 5, involved in signaling cascades that are important for the pathology of joint components. Genome-wide association studies have uncovered a likely role in OA for the genes encoding structural extracellular matrix components (such as DVWA) and molecules involved in prostaglandin metabolism (such as DQB1 and BTNL2). A ∼300 kilobase region in chromosome 7q22 is also associated with OA susceptibility. Finally, the identification of individuals at a high risk of OA and of total joint arthroplasty failure might be facilitated by the use of combinations of genetic markers, allowing for the application of preventive and disease-management strategies.

The genetic epidemiology of osteoarthritis

PURPOSE OF REVIEW

Osteoarthritis is the most common form of arthritis in the elderly and is influenced by both genetic and environmental risk factors. The scope of the present article is to offer an overview of recent developments in the genetic epidemiology of knee and hip osteoarthritis, with particular emphasis on published genomewide association studies (GWAS).

RECENT FINDINGS

Candidate gene studies and genomewide linkage studies have identified genes in the bone morphogenetic pathway (e.g. GDF5), the thyroid regulation pathway (DIO2) and apoptotic pathways as involved in genetic risk of large joint osteoarthritis. GWAS have reported structural genes (COL6A4), inflammation-related genes (PTGS2/PLA2G4A) and a locus on chr 7q22 (GPR22 and four other genes in the same linkage disequilibrium block) associated with osteoarthritis.

SUMMARY

Genetic studies have identified polymorphisms associated with osteoarthritis and related end-points. These include genes in signaling cascades involved in joint and bone biology, as well as genes in inflammatory pathways and a cluster of five genes in perfect linkage disequilibrium in the 7q22 region.

Radiographic severity of knee osteoarthritis is conditional on interleukin 1 receptor antagonist gene variations

BACKGROUND

A lack of biomarkers that identify patients at risk for severe osteoarthritis (OA) complicates development of disease-modifying OA drugs.

OBJECTIVE

To determine whether inflammatory genetic markers could stratify patients with knee OA into high and low risk for destructive disease.

METHODS

Genotype associations with knee OA severity were assessed in two Caucasian populations. Fifteen single nucleotide polymorphisms (SNPs) in six inflammatory genes were evaluated for association with radiographic severity and with synovial fluid mediators in a subset of the patients.

RESULTS

Interleukin 1 receptor antagonist (IL1RN) SNPs (rs419598, rs315952 and rs9005) predicted Kellgren-Lawrence scores independently in each population. One IL1RN haplotype was associated with lower odds of radiographic severity (OR=0.15; 95% CI 0.065 to 0.349; p<0.0001), greater joint space width and lower synovial fluid cytokine levels. Carriage of the IL1RN haplotype influenced the age relationship with severity.

CONCLUSION

IL1RN polymorphisms reproducibly contribute to disease severity in knee OA and may be useful biomarkers for patient selection in disease-modifying OA drug trials.

Primary osteoarthritis no longer primary: three subsets with distinct etiological, clinical, and therapeutic characteristics

BACKGROUND

Osteoarthritis (OA) has been historically divided into primary and secondary. Primary OA has been defined as an idiopathic condition developing in previously undamaged joints in the absence of an obvious causative mechanism. During the last few years a large amount of evidence has provided new insights into the biochemistry and molecular biology of cartilage, subchondral bone, and other articular tissues, which suggest distinct etiopathogenetic mechanisms in some forms of primary OA.

OBJECTIVE

To propose an etiopathogenic classification of primary OA in the light of the significant progress in the understanding of the disease.

METHODS

A review of the literature was performed by searching the Medline and PubMed databases from 1952 to November 2008 using the following keywords: genetic alteration, heritability, estrogen, menopause, and aging either alone or in various combinations with joint, cartilage, subchondral bone, synovium, ligaments, muscle, tendons, OA, and osteoporosis.

RESULTS

Numerous studies have shown that genetic alterations, menopause-related estrogen deficiency, and aging play crucial roles in the molecular pathophysiological events involved in the process of cartilage and joint damage and thus in development of OA. We propose classifying primary OA into 3 distinct although interrelated subsets: type I OA, genetically determined; type II OA, estrogen hormone dependent; and type III OA, aging related.

CONCLUSIONS

The 3 proposed subsets of OA display distinct etiological, clinical, and therapeutic characteristics and should therefore no longer be considered to be "Primary OA."

Genetic and environmental effects on isometric muscle strength and leg extensor power followed up for three years among older female twins

The purpose of this study was to examine changes in the contribution of genetic and environmental effects to isometric knee extensor strength and leg extensor power among 63- to 76-year-old female twins over a 3-yr follow-up. At baseline in 2000 the sample comprised 206 monozygotic (MZ) and 228 dizygotic (DZ) twin individuals, and at follow-up in 2003 the sample comprised 149 MZ and 164 DZ twin individuals. Genetic modeling showed that genetic effects explained 58% (95% CI: 46–68%) of the variance in muscle strength at baseline and 56% (95% CI: 41–68%) at follow-up, with no occasion-specific genetic effect. Nonshared environmental effects accounted for 42% (95% CI: 32–54%) of the variation at baseline and 15% (95% CI: 7–26%) at follow-up. In addition, new nonshared environmental effects explained the remaining variance, 29% (95% CI: 22–37%) of muscle strength at follow-up. For muscle power, the same genetic effects accounted for 67% (95% CI: 57–74%) of the variation at baseline and 48% (95% CI: 34–61%) at follow-up. Nonshared environmental effects in common at both measurement points explained 33% (95% CI: 25–43%) of the total variation at baseline and 11% (95% CI: 5–21%) at follow-up. The remaining variance of muscle power at follow-up was accounted for by time-specific environmental effects. Results indicated that the contribution of genetic effects to isometric muscle strength was stable, whereas for leg extensor power the proportion of genetic effects decreased during the follow-up. We observed new specific environmental effects underlying follow-up muscle strength and power, which effects could be due to the onset of new disease processes or changes in lifestyle.

Bivariate genome-wide linkage analysis of femoral bone traits and leg lean mass: Framingham study

The risk of osteoporotic fracture is a function of both applied muscle mass and bone tissue distribution. Leg lean mass (LLM) and femoral bone geometry are both known to have substantial genetic components. Therefore, we estimated shared heritability (h(2)) and performed linkage analysis to identify chromosomal regions governing both LLM and bone geometry. A genome-wide scan (using 636 microsatellite markers) for linkage analyses was performed on 1346 adults from 327 extended families of the Framingham study. DXA measures were LLM, femoral neck length, neck-shaft angle (NSA), subperiosteal width, cross-sectional area (CSA), and section modulus (Z) at the femoral narrow neck and shaft (S) regions. Variance component linkage analysis was performed on normalized residuals (adjusted for age, height, BMI, and estrogen status in women). The results indicated substantial h(2) for LLM (0.42 +/- 0.07) that was comparable to bone geometry traits. Phenotypic correlations between LLM and bone geometry phenotypes ranged from 0.033 with NSA (p > 0.05) to 0.251 with S_Z (p < 0.001); genetic correlations ranged from 0.087 (NSA, p > 0.05) to 0.454 (S_Z, p < 0.001). Univariate linkage analysis of covariate-adjusted LLM identified no chromosomal regions with LOD scores >or=2.0; however, bivariate analysis identified two loci with LOD scores >3.0, shared by LLM with S_CSA on chromosome 12p12.3-12p13.2, and with NSA, on 14q21.3-22.1. In conclusion, we identified chromosomal regions potentially linked to both LLM and femoral bone geometry. Identification and subsequent characterization of these shared loci may further elucidate the genetic contributions to both osteoporosis and sarcopenia.

The contribution of genes to osteoarthritis

Osteoarthritis (OA) is the most prevalent form of arthritis in the elderly. A large body of evidence, including familial aggregation and classic twin studies, indicates that primary OA has a strong hereditary component that is likely polygenic in nature. Traits related to OA, such as longitudinal changes in cartilage volume and progression of radiographic features, are also under genetic control. In recent years several linkage analyses and candidate gene studies have been performed and unveiled some of the specific genes involved in disease risk, such as FRZB and GDF5. This article discusses the impact that future genome-wide association scans can have on our understanding of the pathogenesis of OA and on identifying individuals at high risk for developing severe OA.

The contribution of genes to osteoarthritis

Osteoarthritis (OA) is the most prevalent form of arthritis in the elderly. A large body of evidence, including familial aggregation and classic twin studies, indicates that primary OA has a strong hereditary component that is likely polygenic in nature. Furthermore, traits related to OA, such as longitudinal changes in cartilage volume and progression of radiographic features, are also under genetic control. In recent years, several linkage analysis and candidate gene studies have been performed and have unveiled some of the specific genes involved in disease risk, such as FRZB and GDF5. The authors discuss the impact that future genome-wide association scans can have on our understanding of the pathogenesis of OA and on identifying individuals at high risk for developing severe OA.

Genetics of the musculoskeletal system: a pleiotropic approach

The risk of osteoporotic fracture can be viewed as a function of loading conditions and the ability of the bone to withstand the load. Skeletal loads are dominated by muscle action. Recently, it has become clear that bone and muscle share genetic determinants. Involution of the musculoskeletal system manifests as bone loss (osteoporosis) and muscle wasting (sarcopenia). Therefore, the consideration of pleiotropy is an important aspect in the study of the genetics of osteoporosis and sarcopenia. This Perspective will provide the evidence for a shared genetic influence on bone and muscle. We will start with an overview of accumulating evidence that physical exercise produces effects on the adult skeleton, seeking to unravel some of the contradictory findings published thus far. We will provide indications that there are pleiotropic relationships between bone structure/mass and muscle mass/function. Finally, we will offer some insights and practical recommendations as to the value of studying shared genetic factors and will explore possible directions for future research. We consider several related questions that together comprise the general paradigm of bone responses to mechanical loading and the relationship between muscle strength and bone parameters, including the genetic factors that modulate these responses. We believe that further progress in understanding the common genetic etiology of osteoporosis and sarcopenia will provide valuable insight into important biological underpinnings for both conditions and may translate into new approaches to reduce the burdens of both conditions through improved diagnosis, prevention, and early targeted treatment.

Allometric relationships between knee cartilage volume, thickness, surface area and body dimensions

OBJECTIVE

To determine if anthropometric factors obtainable on routine examination can be used to estimate premorbid knee total subchondral bone area (tAB), cartilage surface area (AC), cartilage thickness (ThC), and cartilage volume (VC).

METHOD

Young individuals (21-39 years old) without history of knee joint pain, injury or disease were studied. Magnetic resonance imaging of the right knee was used to determine tAB, AC, ThC and VC for knee cartilage. Multilinear regression and curve fitting by variance minimization were used to model the data.

RESULTS

VC and AC closely depended on tAB(1.5) in both men and women. This relationship subsumed all dependency on sex, height, weight and body mass index. In females, VC depended on height cubed and tAB on height squared. The relationship was much weaker in males. ThC was poorly related to tAB and VC. Confidence limits for VC standardized to tAB(1.5) were narrower than standardization to tAB or height.

CONCLUSION

The absence of a tight relationship of VC and tAB with height in males suggests that the factors stimulating bone and cartilage growth may be different between sexes. The high correlation between tAB and VC across both sexes suggests, however, that (opposite to measures from routine clinical examination) tAB(1.5) can provide individual reference values for VC, against which changes with age and disease can be estimated with high confidence.

Tibial subchondral bone size and knee cartilage defects: relevance to knee osteoarthritis

Unlike knee plain radiography which can only detect joint space narrowing and osteophytes, magnetic resonance imaging can directly visualize and analyse the whole knee structure, including bone size, cartilage defects and loss of cartilage volume. Tibial subchondral bone area expansion may be primary and is associated with risk factors such as age, body mass index (BMI), genetics and/or limb malalignment. It can lead to the development of knee defects, which may also be caused by demographic, anthropometric and environmental factors such as age, female sex, BMI and smoking as well as structural changes such as osteophytes, bone marrow lesions, meniscal tears, meniscal extrusion and ligament abnormalities. Once knee cartilage defects develop, they have a variable natural history but are associated with subsequent cartilage loss in a dose-response manner. Both tibial subchondral bone area and knee cartilage defects are quantitatively related to the severity of knee osteoarthritis (OA), and predictive of the need for knee joint replacement in subjects with knee OA independent of radiographic change. Taken as a whole, these studies suggest that tibial subchondral bone expansion and cartilage defect development represent important targets for the prevention of cartilage loss and joint replacement.

Physical Activity and Knee Structural Change

INTRODUCTION

Exercise therapy is effective in improving symptoms of knee osteoarthritis, but its effect on structural change remains unclear.

PURPOSE

To describe the associations between physical activity and structural changes of the knee joint as assessed by magnetic resonance imaging (MRI) in adult male and female subjects.

METHODS

A convenience sample of 325 subjects (mean age 45 yr, range 26-61) was measured at baseline and approximately 2 yr later. Measures of physical activity included questionnaire items, physical work capacity (PWC(170)), and lower-limb muscle strength. Knee cartilage volume, tibial plateau area, and cartilage defect score (0-4) were determined using T1-weighted fat saturation MRI.

RESULTS

Lower-limb muscle strength at baseline was positively associated with both percent-per-year changes in total cartilage volume (r = 0.13) and lateral and total tibial plateau area (r = 0.15 and 0.17) but not other sites. Change in muscle strength was negatively associated with annual changes in lateral and total tibial plateau area (r = -0.13 and -0.17). In females only, PWC170 at baseline was negatively associated with percent-per-year changes in lateral and total cartilage volume (r = -0.16 and -0.17) and positively for lateral and total tibial plateau area (r = 0.18 and 0.16). Conversely, change in PWC(170) was positively associated with changes in cartilage volume at all sites (r = 0.24-0.26). For all associations, P < 0.05.

CONCLUSIONS

Overall, these associations were modest in magnitude, but they suggest that knee cartilage volume and tibial plateau area are dynamic structures that can respond to physical stimuli. Greater muscle strength and endurance fitness, especially in women, may be protective against cartilage loss, but it also may result in a maladaptive enlargement of subchondral bone in both sexes, suggesting that physical activity may have both good and bad effects on the knee.

Familial, structural, and environmental correlates of MRI-defined bone marrow lesions: a sibpair study

The aim of this study was to estimate the heritability and describe the correlates of bone marrow lesions in knee subchondral bone. A sibpair design was used. T2- and T1-weighted MRI scans were performed on the right knee to assess bone marrow lesions at lateral tibia and femora and medial tibia and femora, as well as chondral defects. A radiograph was taken on the same knee and scored for individual features of osteoarthritis (radiographic osteoarthritis; ROA) and alignment. Other variables measured included height, weight, knee pain, and lower-limb muscle strength. Heritability was estimated with the program SOLAR (Sequential Oligogenetic Linkage Analysis Routines). A total of 115 siblings (60 females and 55 males) from 48 families, representing 95 sib pairs, took part. The adjusted heritability estimates were 53 +/- 28% (mean +/- SEM; p = 0.03) and 65 +/- 32% (p = 0.03) for severity of bone marrow lesions at lateral and medial compartments, respectively. The estimates were reduced by 8 to 9% after adjustment for chondral defects and ROA (but not alignment). The adjusted heritability estimate was 99% for prevalent bone marrow lesions at both lateral and medial compartments. Both lateral and medial bone marrow lesions were significantly correlated with age, chondral defects, and ROA of the knee (all p < 0.05). Medial bone marrow lesions were also more common in males and were correlated with body mass index (BMI). Thus, bone marrow lesions have a significant genetic component. They commonly coexist with chondral defects and ROA but only share common genetic mechanisms to a limited degree. They are also more common with increasing age, male sex, and increasing BMI.

Knee cartilage loss in symptomatic knee osteoarthritis over 4.5 years

The objective of this study was to describe the rate of change in knee cartilage volume over 4.5 years in subjects with symptomatic knee osteoarthritis (OA) and to determine factors associated with cartilage loss. One hundred and five subjects were eligible for this longitudinal study. Subjects' tibial cartilage volume was assessed by magnetic resonance imaging (MRI) at baseline, at 2 years and at 4.5 years. Of 105 subjects, 78 (74%) completed the study. The annual percentage losses of medial and lateral tibial cartilage over 4.5 years were 3.7 ± 4.7% (mean ± SD; 95% confidence interval 2.7 to 4.8%) and 4.4 ± 4.7% (mean ± SD; 95% confidence interval 3.4 to 5.5%), respectively. Cartilage volume in each individual seemed to track over the study period, relative to other study participants. After multivariate adjustment, annual medial tibial cartilage loss was predicted by lesser severity of baseline knee pain but was independent of age, body mass index and structural factors. No factors specified a priori were associated with lateral cartilage volume rates of change. Tibial cartilage declines at an average rate of 4% per year in subjects with symptomatic knee OA. There was evidence to support the concept that tracking occurs in OA. This may enable the prediction of cartilage change in an individual. The only significant factor affecting the loss of medial tibial cartilage was baseline knee pain, possibly through altered joint loading.

Genetic influence on the progression of radiographic knee osteoarthritis: a longitudinal twin study

OBJECTIVE

Genetic influences on rates of osteoarthritis (OA) progression are unknown. Our aim was to estimate the heritability of progression of radiographic knee OA using a longitudinal twin study.

METHODS

Unselected monozygotic (MZ) and dizygotic (DZ) twin pairs from the TwinsUK registry were utilized. Anteroposterior radiographs were performed on both knees at baseline and follow-up using the same protocol. Radiographic features of knee OA including osteophyte and joint space narrowing (JSN) were assessed on a four-point scale using a standard atlas. Progression of knee osteophyte and JSN was defined as the difference in the corresponding score between follow-up and baseline > or =1. Liability threshold modelling using logistic regression was utilized for heritability estimation.

RESULTS

A total of 114 MZ pairs and 195 DZ pairs were studied. The average follow-up time was 7.2 years. Medial progression of osteophyte and JSN was more common than lateral progression. Prevalence of progression was generally higher in the MZs than the DZs. Similarly, concordances and tetrachoric correlations for both osteophyte and JSN were higher in the MZs than the DZs although only significant for overall and medial JSN and osteophyte. The heritability estimates were 69% [95% confidence interval (CI) 42-97%] and 80% (95% CI 50-100%) for medial osteophyte and JSN, respectively. The estimates were reduced by 7-15% after adjustment for age, body mass index (BMI), and the severity of osteophyte/JSN at baseline.

CONCLUSION

Our data documented a substantial genetic influence on the progression of knee OA--as seen in the medial compartment, providing a solid basis to search for genes involved in this highly relevant clinical trait.

Genetic mechanisms of knee osteoarthritis: a population-based longitudinal study

To describe the differences in knee structure and non-knee structural factors between offspring having at least one parent with a total knee replacement for severe primary knee osteoarthritis and age- and sex-matched controls with no family history of knee osteoarthritis, a population-based longitudinal study of 163 matched pairs (mean age 45 years, range 26 to 61) was performed at baseline and about 2 years later. Knee cartilage defect score (0 to 4), cartilage volume and bone size were determined with T1-weighted fat saturation magnetic resonance imaging. Body mass index (BMI), lower-limb muscle strength, knee pain, physical work capacity at 170 beats/minute (PWC170) and radiographic osteoarthritis were measured by standard protocols. In comparison with controls, offspring had higher annual knee cartilage loss (-3.1% versus -2.0% at medial tibial site, -1.9% versus -1.1% at lateral tibial site and -4.7% versus -3.7% at patellar site, all P < 0.05), a greater increase in medial cartilage defect score (+0.15 versus -0.01, P < 0.05) and a greater decline in PWC170 (-0.7 watts/kg versus -0.4 watts/kg, P < 0.01). There were no significant differences in change in BMI, lower-limb muscle strength, knee pain or tibial bone area between these two groups; however, the differences in knee cartilage loss and cartilage defect change decreased in magnitude and became non-significant after adjustment for baseline cartilage volume, tibial bone area, BMI and knee pain. This longitudinal study suggests that knee cartilage loss, change in cartilage defects and decrease in physical fitness all have roles in the development of knee osteoarthritis, which is most probably polygenic but may reflect a shared environment. Importantly, the cartilage changes are largely dependent on baseline differences in cartilage volume, tibial bone area, BMI and knee pain, suggesting that these factors might have a role in their initiation.

Smoking interacts with family history with regard to change in knee cartilage volume and cartilage defect development

OBJECTIVE

To describe the effects of smoking on change in knee cartilage volume and increases in knee cartilage defects, and to test for interaction between smoking and family history of osteoarthritis (OA).

METHODS

Subjects with at least 1 parent having severe primary knee OA (offspring) and randomly selected controls without this history (a total of 325 subjects with a mean age of 45 years) were measured at baseline and 2.3 years later. Knee cartilage volume and defect score (on a 0-4 scale) were determined using T1-weighted fat-saturated magnetic resonance imaging. Smoking status and duration and number of cigarettes were recorded by questionnaire.

RESULTS

In offspring, smoking was associated with annual change in medial and lateral tibial cartilage volume (beta = -2.20% and beta = -1.45%, respectively, for current smokers versus former smokers and those who had never smoked; beta = -0.07%/pack-year at both tibial sites, for smoking severity) in multivariate analysis. Smoking was also associated with increases (change >or=1) in medial and lateral tibiofemoral cartilage defect scores (odds ratio [OR] 4.91 and OR 2.98, respectively, for current smokers versus those who had never smoked; OR 9.90 and OR 12.98, respectively, for heavy smoking [total of >20 pack-years] versus never smoking) (all P < 0.05). In contrast, smoking was not associated with any of the above in controls except for change in lateral tibial cartilage volume. There was significant interaction between smoking and offspring-control status for change in medial tibial cartilage volume (P = 0.047) and increases in medial (P = 0.03) and lateral (P = 0.049) tibiofemoral cartilage defects.

CONCLUSION

Smoking leads to knee cartilage loss and defect development primarily in individuals with a family history of knee OA. This provides evidence for a gene-environment interaction in the etiology of knee OA.

Quantitative MRI of cartilage and bone: degenerative changes in osteoarthritis

Magnetic resonance imaging (MRI) and quantitative image analysis technology has recently started to generate a great wealth of quantitative information on articular cartilage and bone physiology, pathophysiology and degenerative changes in osteoarthritis. This paper reviews semiquantitative scoring of changes of articular tissues (e.g. WORMS = whole-organ MRI scoring or KOSS = knee osteoarthritis scoring system), quantification of cartilage morphology (e.g. volume and thickness), quantitative measurements of cartilage composition (e.g. T2, T1rho, T1Gd = dGEMRIC index) and quantitative measurement of bone structure (e.g. app. BV/TV, app. TbTh, app. Tb.N, app. Tb.Sp) in osteoarthritis. For each of these fields we describe the hardware and MRI sequences available, the image analysis systems and techniques used to derive semiquantitative and quantitative parameters, the technical accuracy and precision of the measurements reported to date and current results from cross-sectional and longitudinal studies in osteoarthritis. Moreover, the paper summarizes studies that have compared MRI-based measurements with radiography and discusses future perspectives of quantitative MRI in osteoarthritis. In summary, the above methodologies show great promise for elucidating the pathophysiology of various tissues and identifying risk factors of osteoarthritis, for developing structure modifying drugs (DMOADs) and for combating osteoarthritis with new and better therapy.

Epidemiology of osteoarthritis: an update

PURPOSE OF REVIEW

As the most common arthritis and a leading cause of chronic disability, osteoarthritis is associated with substantial cost to the individual and to society. Epidemiologic studies have supplied, in addition to incidence, prevalence and risk factor data, much of what is known about the natural history of osteoarthritis.

RECENT FINDINGS

Especially given the anticipated increase in osteoarthritis prevalence, the need to identify risk factors for incident osteoarthritis, osteoarthritis progression, osteoarthritis-associated physical function decline, and disability is a high priority. As this review illustrates, the emphasis has shifted in osteoarthritis epidemiology towards the identification of risk factors for osteoarthritis progression rather than incidence.

SUMMARY

Several risk factors for progression are emerging, many of which are impairments or pathology in the local joint organ environment. This shift in focus relates in part to the concept that local risk factors might ultimately be targeted to delay osteoarthritis progression or to enhance the effect of a disease-modifying drug.

Magnetic resonance imaging (MRI) of articular cartilage in knee osteoarthritis (OA): morphological assessment

OBJECTIVE

Magnetic resonance imaging (MRI) is a three-dimensional imaging technique with unparalleled ability to evaluate articular cartilage. This report reviews the current status of morphological assessment of cartilage with quantitative MRI (qMRI), and its relevance for identifying disease status, and monitoring progression and treatment response in knee osteoarthritis (OA).

METHOD

An international panel of experts in MRI of knee OA, with direct experience in the analysis of cartilage morphology with qMRI, reviewed the existing published and unpublished data on the subject, and debated the findings at the OMERACT-OARSI Workshop on Imaging technologies (December 2002, Bethesda, MA) with scientists and clinicians from academia, the pharmaceutical industry and the regulatory agencies. This report reviews (1) MRI pulse sequence considerations for morphological analysis of articular cartilage; (2) techniques for segmenting cartilage; (3) semi-quantitative scoring of cartilage status; and (4) technical validity (accuracy), precision (reproducibility) and sensitivity to change of quantitative measures of cartilage morphology.

RESULTS

Semi-quantitative scores of cartilage status have been shown to display adequate reliability, specificity and sensitivity, and to detect lesion progression at reasonable observation periods (1-2 years). Quantitative assessment of cartilage morphology (qMRI), with fat-suppressed gradient echo sequences, and appropriate image analysis techniques, displays high accuracy and adequate precision (e.g., root-mean-square standard deviation medial tibia=61 microl) for cross-sectional and longitudinal studies in OA patients. Longitudinal studies suggest that changes of cartilage volume of the order of -4% to -6% occur per annum in OA in most knee compartments (e.g., -90 microl in medial tibia). Annual changes in cartilage volume exceed the precision errors and appear to be associated with clinical symptoms as well as with time to knee arthroplasty.

CONCLUSIONS

MRI provides reliable and quantitative data on cartilage status throughout most compartments of the knee, with robust acquisition protocols for multi-center trials now being available. MRI of cartilage has tremendous potential for large scale epidemiological studies of OA progression, and for clinical trials of treatment response to structure modifying OA drugs.