The genetics of intervertebral disc degeneration.Associated genes

Genetic polymorphisms associated with intervertebral disc degeneration

BACKGROUND CONTEXT

Disc degeneration (DD) is a multifaceted chronic process that alters the structure and function of the intervertebral discs and can lead to painful conditions. The pathophysiology of degeneration is not well understood, but previous studies suggest that certain genetic polymorphisms may be important contributing factors leading to an increased risk of DD.

PURPOSE

To review the genetic factors in DD with a focus on polymorphisms and their putative role in the pathophysiology of degeneration. Elucidating the genetic components that are associated with degeneration could provide insights into the mechanism of the process. Furthermore, defining these relationships and eventually using them in a clinical setting may allow an identification and early intervention for those who are at a high risk for painful DD.

STUDY DESIGN

Literature review.

METHODS

This literature review focused on the studies concerning genetic polymorphisms and their associations with DD.

RESULTS

Genetic polymorphisms in 20 genes have been analyzed in association with DD, including vitamin D receptor, growth differentiation factor 5 (GDF5), aggrecan, collagen Types I, IX, and XI, fibronectin, hyaluronan and proteoglycan link protein 1 (HAPLN1), thrombospondin, cartilage intermediate layer protein (CILP), asporin, MMP1, 2, and 3, parkinson protein 2, E3 ubiquitin protein ligase (PARK2), proteosome subunit β type 9 (PSMB9), tissue inhibitor of metalloproteinase (TIMP), cyclooxygenase-2 (COX2), and IL1α, IL1β, and IL6. Each genetic polymorphism codes for a protein that has a functional role in the pathogenesis of DD.

CONCLUSIONS

There are known associations between several genetic polymorphisms and DD. Of the 20 genes analyzed, polymorphisms in vitamin D receptor, aggrecan, Type IX collagen, asporin, MMP3, IL1, and IL6 show the most promise as functional variants. Genetic studies are crucial for understanding the mechanism of the degeneration. This genetic information could eventually be used as a predictive model for determining a patient's risk for symptomatic DD.

Low back pain and lumbar spine osteoarthritis: how are they related?

Lumbar spine osteoarthritis (OA) is very common, with estimates of prevalence ranging from 40-85 %. The process of degeneration of the spine has commonly been classified as OA (disc space narrowing together with vertebral osteophyte formation); however, anatomically, the facet joint is the only synovial joint in the spine that has a similar pathological degenerative process to appendicular joints. Low back pain (LBP) is also a common condition, with nearly 80 % of Americans experiencing at least one episode of LBP in their lifetime. The complex relationship between spine radiographs and LBP has many clinical and research challenges. Specific conservative treatments for spine degeneration have not been established; there has, however, been recent interest in use of exercise therapy, because of some moderate benefits in treating chronic LBP. An understanding of the relationship between spine degeneration and LBP may be improved with further population-based research in the areas of genetics, biomarkers, and pain pathways.

Stemming the Degeneration: IVD Stem Cells and Stem Cell Regenerative Therapy for Degenerative Disc Disease

The intervertebral disc (IVD) is immensely important for the integrity of vertebral column function. The highly specialized IVD functions to confer flexibility and tensile strength to the spine and endures various types of biomechanical force. Degenerative disc disease (DDD) is a prevalent musculoskeletal disorder and is the major cause of low back pain and includes the more severe degenerative lumbar scoliosis, disc herniation and spinal stenosis. DDD is a multifactorial disorder whereby an imbalance of anabolic and catabolic factors, or alterations to cellular composition, or biophysical stimuli and genetic background can all play a role in its genesis. However, our comprehension of IVD formation and theetiology of disc degeneration (DD) are far from being complete, hampering efforts to formulate appropriate therapies to tackle DD. Knowledge of the stem cells and various techniques to manipulate and direct them to particular fates have been promising in adopting a stem-cell based regenerative approach to DD. Moreover, new evidence on the residence of stem/progenitor cells within particular IVD niches has emerged holding promise for future therapeutic applications. Existing issues pertaining to current therapeutic approaches are also covered in this review.

Genetic association studies in lumbar disc degeneration: a systematic review

Objective

Low back pain is associated with lumbar disc degeneration, which is mainly due to genetic predisposition. The objective of this study was to perform a systematic review to evaluate genetic association studies in lumbar disc degeneration as defined on magnetic resonance imaging (MRI) in humans.

Methods

A systematic literature search was conducted in MEDLINE, MEDLINE In-Process, SCOPUS, ISI Web of Science, The Genetic Association Database and The Human Genome Epidemiology Network for information published between 1990–2011 addressing genes and lumbar disc degeneration. Two investigators independently identified studies to determine inclusion, after which they performed data extraction and analysis. The level of cumulative genetic association evidence was analyzed according to The HuGENet Working Group guidelines.

Results

Fifty-two studies were included for review. Forty-eight studies reported at least one positive association between a genetic marker and lumbar disc degeneration. The phenotype definition of lumbar disc degeneration was highly variable between the studies and replications were inconsistent. Most of the associations presented with a weak level of evidence. The level of evidence was moderate for ASPN (D-repeat), COL11A1 (rs1676486), GDF5 (rs143383), SKT (rs16924573), THBS2 (rs9406328) and MMP9 (rs17576).

Conclusions

Based on this first extensive systematic review on the topic, the credibility of reported genetic associations is mostly weak. Clear definition of lumbar disc degeneration phenotypes and large population-based cohorts are needed. An international consortium is needed to standardize genetic association studies in relation to disc degeneration.

Elevated plasma levels of TIMP-1 in patients with rotator cuff tear

BACKGROUND AND PURPOSE

Extracellular matrix remodeling is altered in rotator cuff tears, partly due to altered expression of matrix metalloproteinases (MMPs) and their inhibitors. It is unclear whether this altered expression can be traced as changes in plasma protein levels. We measured the plasma levels of MMPs and their tissue inhibitors (TIMPs) in patients with rotator cuff tears and related changes in the pattern of MMP and TIMP levels to the extent of the rotator cuff tear.

METHODS

Blood samples were collected from 17 patients, median age 61 (39-77) years, with sonographically verified rotator cuff tears (partial- or full-thickness). These were compared with 16 age- and sex-matched control individuals with sonographically intact rotator cuffs. Plasma levels of MMPs and TIMPs were measured simultaneously using Luminex technology and ELISA.

RESULTS

The plasma levels of TIMP-1 were elevated in patients with rotator cuff tears, especially in those with full-thickness tears. The levels of TIMP-1, TIMP-3, and MMP-9 were higher in patients with full-thickness tears than in those with partial-thickness tears, but only the TIMP-1 levels were significantly different from those in the controls.

INTERPRETATION

The observed elevation of TIMP-1 in plasma might reflect local pathological processes in or around the rotator cuff, or a genetic predisposition in these patients. That the levels of TIMP-1 and of certain MMPs were found to differ significantly between partial and full-thickness tears may reflect the extent of the lesion or different etiology and pathomechanisms.

Degenerative joint disease of the spine

Degenerative changes are the manifestations of metabolic disturbances in the matrix of intervertebral disks and zygapophysial joints. Genetic factors and physical loading contribute, but the strongest correlation is with age. Degenerative changes lack any significant correlation with spinal pain. Therefore, they do not constitute a diagnosis. Internal disk disruption is a distinctive condition that is independent of degeneration and age. Its biophysical and morphologic features correlate with back pain, as do its manifestations on magnetic resonance imaging.

Lumbar degenerative disc disease: current and future concepts of diagnosis and management

Low back pain as a result of degenerative disc disease imparts a large socioeconomic impact on the health care system. Traditional concepts for treatment of lumbar disc degeneration have aimed at symptomatic relief by limiting motion in the lumbar spine, but novel treatment strategies involving stem cells, growth factors, and gene therapy have the theoretical potential to prevent, slow, or even reverse disc degeneration. Understanding the pathophysiological basis of disc degeneration is essential for the development of treatment strategies that target the underlying mechanisms of disc degeneration rather than the downstream symptom of pain. Such strategies ideally aim to induce disc regeneration or to replace the degenerated disc. However, at present, treatment options for degenerative disc disease remain suboptimal, and development and outcomes of novel treatment options currently have to be considered unpredictable.

Simulated-physiological loading conditions preserve biological and mechanical properties of caprine lumbar intervertebral discs in ex vivo culture

Low-back pain (LBP) is a common medical complaint and associated with high societal costs. Degeneration of the intervertebral disc (IVD) is assumed to be an important causal factor of LBP. IVDs are continuously mechanically loaded and both positive and negative effects have been attributed to different loading conditions.

In order to study mechanical loading effects, degeneration-associated processes and/or potential regenerative therapies in IVDs, it is imperative to maintain the IVDs' structural integrity. While in vivo models provide comprehensive insight in IVD biology, an accompanying organ culture model can focus on a single factor, such as loading and may serve as a prescreening model to reduce life animal testing. In the current study we examined the feasibility of organ culture of caprine lumbar discs, with the hypothesis that a simulated-physiological load will optimally preserve IVD properties.

Lumbar caprine IVDs (n = 175) were cultured in a bioreactor up to 21 days either without load, low dynamic load (LDL), or with simulated-physiological load (SPL). IVD stiffness was calculated from measurements of IVD loading and displacement. IVD nucleus, inner- and outer annulus were assessed for cell viability, cell density and gene expression. The extracellular matrix (ECM) was analyzed for water, glycosaminoglycan and total collagen content.

IVD biomechanical properties did not change significantly with loading conditions. With SPL, cell viability, cell density and gene expression were preserved up to 21 days. Both unloaded and LDL resulted in decreased cell viability, cell density and significant changes in gene expression, yet no differences in ECM content were observed in any group.

In conclusion, simulated-physiological loading preserved the native properties of caprine IVDs during a 21-day culture period. The characterization of caprine IVD response to culture in the LDCS under SPL conditions paves the way for controlled analysis of degeneration- and regeneration-associated processes in the future.

Cartilage intermediate layer protein (CILP) regulation in intervertebral discs. The effect of age, degeneration, and bone morphogenetic protein-2

STUDY DESIGN

An in vitro study using rabbit intervertebral disc tissue and disc cells.

OBJECTIVE

To evaluate the effects of disc degeneration, age, and bone morphogenetic proteins-2 (BMP-2) on cartilage intermediate layer protein (CILP) expression and elucidate the molecular mechanism by which BMP-2 regulates CILP expression.

SUMMARY OF BACKGROUND DATA

CILP is implicated in several diseases that affect cartilage. The CILP polymorphism acts as a modulator of lumbar disc disease susceptibility. However, regulation of the CILP gene in disc tissue remains poorly understood.

METHODS

Intact discs from young rabbits were punctured to induce disc degeneration. These young rabbits and other older rabbits were used to measure the expression of CILP, proteoglycan, and collagen II using Western blot and real-time PCR. Primary disc cells from the rabbits were treated with rhBMP-2, or siRNAs, and the gene expression was analyzed by Western blot and real-time PCR. The activity of the CILP promoter was measured by using the Dual Luciferase Reporter Assay System.

RESULTS

Our study demonstrates that the intervertebral disc expresses significant levels of CILP and that the expression of CILP increases substantially with increasing age and disc degeneration. In contrast, the expression of proteoglycan and collagen II decrease with increasing age and disc degeneration. BMP-2 induces the expression of CILP protein and stimulates the activity of the CILP promoter in rabbit primary disc cells. The induction of CILP by BMP-2 can be augmented with age. Knockdown of Smad1 by siRNA abolishes the stimulatory effects of BMP-2 on CILP expression in the primary disc cells.

CONCLUSION

Our data demonstrate that disc degeneration, age, and BMP-2 are regulators of the CILP gene. BMP-2 induces CILP expression by activating the Smad1 signal pathway.

Non-specific low back pain

Non-specific low back pain has become a major public health problem worldwide. The lifetime prevalence of low back pain is reported to be as high as 84%, and the prevalence of chronic low back pain is about 23%, with 11-12% of the population being disabled by low back pain. Mechanical factors, such as lifting and carrying, probably do not have a major pathogenic role, but genetic constitution is important. History taking and clinical examination are included in most diagnostic guidelines, but the use of clinical imaging for diagnosis should be restricted. The mechanism of action of many treatments is unclear, and effect sizes of most treatments are low. Both patient preferences and clinical evidence should be taken into account for pain management, but generally self-management, with appropriate support, is recommended and surgery and overtreatment should be avoided.

Genetic susceptibility of intervertebral disc degeneration among young Finnish adults

BACKGROUND

Disc degeneration (DD) is a common condition that progresses with aging. Although the events leading to DD are not well understood, a significant genetic influence has been found. This study was undertaken to assess the association between relevant candidate gene polymorphisms and moderate DD in a well-defined and characterized cohort of young adults. Focusing on young age can be valuable in determining genetic predisposition to DD.

METHODS

We investigated the associations of existing candidate genes for DD among 538 young adults with a mean age of 19 belonging to the 1986 Northern Finland Birth Cohort. Nineteen single nucleotide polymorphisms (SNP) in 16 genes were genotyped. We evaluated lumbar DD using the modified Pfirrmann classification and a 1.5-T magnetic resonance scanner for imaging.

RESULTS

Of the 538 individuals studied, 46% had no degeneration, while 54% had DD and 51% of these had moderate DD. The risk of DD was significantly higher in subjects with an allele G of IL6 SNPs rs1800795 (OR 1.45, 95% CI 1.07-1.96) and rs1800797 (OR 1.37, 95% CI 1.02-1.85) in the additive inheritance model. The role of IL6 was further supported by the haplotype analysis, which resulted in an association between the GGG haplotype (SNPs rs1800797, rs1800796 and rs1800795) and DD with an OR of 1.51 (95% CI 1.11-2.04). In addition, we observed an association between DD and two other polymorphisms, SKT rs16924573 (OR 0.27 95% CI 0.07-0.96) and CILP rs2073711 in women (OR 2.04, 95% CI 1.07-3.89).

CONCLUSION

Our results indicate that IL6, SKT and CILP are involved in the etiology of DD among young adults.

Histological analysis of surgical lumbar intervertebral disc tissue provides evidence for an association between disc degeneration and increased body mass index

Background

Although histopathological grading systems for disc degeneration are frequently used in research, they are not yet integrated into daily care routine pathology of surgical samples. Therefore, data on histopathological changes in surgically excised disc material and their correlation to clinical parameters such as age, gender or body mass index (BMI) is limited to date. The current study was designed to correlate major physico-clinical parameters from a population of orthopaedic spine center patients (gender, age and BMI) with a quantitative histologic degeneration score (HDS).

Methods

Excised lumbar disc material from 854 patients (529 men/325 women/mean age 56 (15-96) yrs.) was graded based on a previously validated histologic degeneration score (HDS) in a cohort of surgical disc samples that had been obtained for the treatment of either disc herniation or discogenic back pain. Cases with obvious inflammation, tumor formation or congenital disc pathology were excluded. The degree of histological changes was correlated with sex, age and BMI.

Results

The HDS (0-15 points) showed significantly higher values in the nucleus pulposus (NP) than in the annulus fibrosus (AF) (Mean: NP 11.45/AF 7.87), with a significantly higher frequency of histomorphological alterations in men in comparison to women. Furthermore, the HDS revealed a positive significant correlation between the BMI and the extent of histological changes. No statistical age relation of the degenerative lesions was seen.

Conclusions

This study demonstrated that histological disc alterations in surgical specimens can be graded in a reliable manner based on a quantitative histologic degeneration score (HDS). Increased BMI was identified as a positive risk factor for the development of symptomatic, clinically significant disc degeneration.

Investigation of different cell types and gel carriers for cell-based intervertebral disc therapy, in vitro and in vivo studies

Biological treatment options for the repair of intervertebral disc damage have been suggested for patients with chronic low back pain. The aim of this study was to investigate possible cell types and gel carriers for use in the regenerative treatment of degenerative intervertebral discs (IVD). In vitro: human mesenchymal cells (hMSCs), IVD cells (hDCs), and chondrocytes (hCs) were cultivated in three gel types: hyaluronan gel (Durolane®), hydrogel (Puramatrix®), and tissue-glue gel (TISSEEL®) in chondrogenic differentiation media for 9 days. Cell proliferation and proteoglycan accumulation were evaluated with microscopy and histology. In vivo: hMSCs or hCs and hyaluronan gel were co-injected into injured IVDs of six minipigs. Animals were sacrificed at 3 or 6 months. Transplanted cells were traced with anti-human antibodies. IVD appearance was visualized by MRI, immunohistochemistry, and histology. Hyaluronan gel induced the highest cell proliferation in vitro for all cell types. Xenotransplanted hMSCs and hCs survived in porcine IVDs for 6 months and produced collagen II in all six animals. Six months after transplantation of cell/gel, pronounced endplate changes indicating severe IVD degeneration were observed at MRI in 1/3 hC/gel, 1/3 hMSCs/gel and 1/3 gel only injected IVDs at MRI and 1/3 hMSC/gel, 3/3 hC/gel, 2/3 gel and 1/3 injured IVDs showed positive staining for bone mineralization. In 1 of 3 discs receiving hC/gel, in 1 of 3 receiving hMSCs/gel, and in 1 of 3 discs receiving gel alone. Injected IVDs on MRI results in 1 of 3 hMSC/gel, in 3 of 3 hC/gel, in 2 of 3 gel, and in 1 of 3 injured IVDs animals showed positive staining for bone mineralization. The investigated hyaluronan gel carrier is not suitable for use in cell therapy of injured/degenerated IVDs. The high cell proliferation observed in vitro in the hyaluronan could have been a negative factor in vivo, since most cell/gel transplanted IVDs showed degenerative changes at MRI and positive bone mineralization staining. However, this xenotransplantation model is valuable for evaluating possible cell therapy strategies for human degenerated IVDs.

Genetics of the degenerated intervertebral disc

BACKGROUND

Given the genetic and proteomic advances of the past decade, understanding of the molecular etiopathogenesis of several complex diseases is increasing. Intervertebral disc disease (IVDD) is no different from other complex diseases where both environmental and genetic constituents are considered causes. This concept has challenged the traditional view that age, occupation, smoking, obesity, and primarily wear and tear are the only sources of disc degeneration.

METHODS

We conducted a systematic Medline review of the most current articles related to gene involvement in the development of IVDD in humans.

RESULTS

Candidate gene linkage and association studies involving the functional components of the intervertebral disc, including collagen I, collagen IX, collagen XI, aggrecan, extracellular matrix-degrading enzymes, inflammatory cytokines (IL-1, IL-6, and TNFα), Fas/FasL and vitamin D receptors, have had promising results.

CONCLUSIONS

This review emphasizes the latest advances in gene association with specific degenerated disc phenotypes, single nucleotide polymorphisms, disease heredity, and gene-environmental interactions in relation to IVDD to help improve future studies related to the genetic mechanisms underlying IVDD.

Genetics of lumbar disk degeneration: technology, study designs, and risk factors

Lumbar disk degeneration (LDD) is a common musculoskeletal condition. Genetic risk factors have been suggested to play a major role in its cause. This article reviews the main research strategies that have been used to study the genetics of LDD, and the genes that thus far have been identified to influence susceptibility to LDD. With the rapid progress in genomic technologies, further advances in the genetics of LDD are expected in the next few years.

Age-related changes in human cervical, thoracal and lumbar intervertebral disc exhibit a strong intra-individual correlation

INTRODUCTION

Intervertebral disc (IVD) degeneration is characterized as a multifactorial disease, in which the hereditary background is thought to be of high importance. Accordingly, one would expect all spinal levels (lumbar/cervical/thoracal) to be affected by above-average disc degeneration in genetically predisposed individuals. The aim of this study, therefore, was to analyze the amount of degenerative changes in different spine levels in humans from different ages.

MATERIALS AND METHODS

In detail, the presence, localization and abundance of histomorphological changes in the annulus fibrosus (AF) and nucleus pulposus (NP) in the cervical (C5/C6), thoracic (T2/T3) and lumbar (L2/L3) spine were investigated in complete autopsy IVD specimens (47 individuals) covering a complete age range (0-95 years).

RESULTS

Results indicate that the highest degree of histo-degenerative changes were observed in the NP in all spine levels and showed an age-related expression pattern. With regard to the different spine levels, lumbar disc specimen showed significantly more degenerative changes compared to cervical and thoracic discs, whereas no statistical difference was observed between cervical and thoracic discs. In summary, highest grades of degeneration were observed in lumbar discs (especially in the NP). Intra-individual correlations between the degeneration score in the different levels showed a significant individual concordance.

CONCLUSIONS

The intra-individual correlation of degenerative changes in all three examined spine regions further supports the notion that individual, i.e. genetic factors are strong predisposing factor for the development of age-related disc alterations.

Caspase 9 gene polymorphism and susceptibility to lumbar disc disease in the Han population in northern China

Many studies have demonstrated that apoptosis is involved in the development of disc degeneration. The initiator caspase 9 is activated through the apoptosome-driven intrinsic apoptotic pathway. The present study aimed to assess the potential association between the caspase 9 gene polymorphism and lumbar disc herniation (LDH) susceptibility, as well as severe grades of disc degeneration in the Han population in northern China. Genotyping was performed using the polymerase chain reaction and polymorphism was analyzed by restriction endonuclease cleavage in 387 patients with LDH and 412 control subjects. The allelic frequencies of caspase 9 Ex5+32 A were 0.483 and 0.391 in case patients and control subjects, respectively. Compared to those with the AA genotype, subjects with the GA/GG genotype have a higher risk to develop LDH (odds ratio 1.91; 95% confidence interval 1.29-2.81). Moreover, the GA/GG genotype was found to contribute to the risk of more severe grades of disc degeneration, as observed in magnetic resonance imaging scan. In conclusion, this study suggests that the single nucleotide polymorphism in the caspase 9 Ex5 + 32 G/A may be associated with LDH and disc degeneration in the Han population of northern China.

The association of aggrecan gene polymorphism with the risk of intervertebral disc degeneration

BACKGROUND

Intervertebral disc degeneration is now considered to be genetically determined in large part, with environmental factors also playing an important role. The human is known to uniquely exhibit variable numbers of tandem repeat polymorphism within the aggrecan CS1 domain. To date, the analysis of aggrecan's variable numbers of tandem repeat polymorphism has given inconsistent results with respect to the correlation between the allele's size and intervertebral disc degeneration. We wanted to investigate the patterns of the variable numbers of tandem repeat polymorphism in the aggrecan CS1 domain of Koreans, and we analyzed the association between the polymorphism and intervertebral disc degeneration.

METHOD

A total of 66 males and 38 females participated in this study. Their ages ranged from 13 to 73 years. Genomic deoxyribonucleic acid was extracted from blood samples and PCR was carried out to detect the alleles of the aggrecan gene. The subjects were evaluated on MRI and they were classified by the number, severity, and morphology of disc degeneration.

FINDINGS

The genotyping identified 11 alleles ranging from 21 to 36 repeats. Alleles 13, 18, 19, and 20 were not found in this study. Of the 104 subjects, 29 (28%) were homozygotes and 75 (72%) were heterozygotes. Allele 27 (39%) was the most common form together with alleles 26 (26%) and 28 (14%). The allele 36 is the longest among the alleles ever discovered. For the case that the analysis was limited to subjects with the fourth decades or less, the 21 allele was significantly overrepresented among the persons with multilevel disc degeneration (p < 0.006).

CONCLUSIONS

Carrying a copy of the allele with 21 repeats might increase the risk of multiple disc degeneration in the subjects below the age of 40 years.

[The spinal intervertebral disc]

The spinal intervertebral disc can cause neurocompression or pain as a result of degeneration. Surgical interventions, therefore, include decompression, fusion, disc replacement or a combination thereof. Identifying the painful segment in the case of axial pain requires accurate segment diagnosis and may require invasive diagnostic measures (joint infiltration, discography), since imaging is often not fluid enough. In the case of fusion following disc removal, the placeholder is substitued in the form of a cage or autologous iliac crest graft. Alternatively, when dorsal elements are intact, a disc prosthesis can be inserted. In the case of compression, removal of the compromised structures (disc, osteophytes) becomes necessary. If the indication is correctly made and the appropriate surgical technique used, good results can be expected from cervical spine surgery.

Risk factors for lumbar intervertebral disc herniation in Chinese population: a case-control study

STUDY DESIGN

A case-control study of 4180 subjects was carried.

OBJECTIVE

To explore the risk factors of lumbar disc herniation in China.

SUMMARY OF BACKGROUND DATA

In China, along with the economic development, people's living environment and working conditions have undergone some tremendous changes, such as the accelerating life pace and competition. In this situation, it is important to know whether the risk factors of lumbar disc herniation have changed or not. This case-control study, including the possible social and psychological factors based on the literature, attempted to search the new risk factor, therefore provide better prevention measures for lumbar disc herniation.

METHODS

A total of 2010 hospitalized patients, diagnosed with lumbar disc protrusion by CT and/or MRI were selected as cases. A total of 2070 people from communities and hospitals, without history of low back pain and sciatica, were selected as controls. All patients and controls were investigated for their family history, occupational characters' smoking status, working psychosocial factors, etc. The risk factors were analyzed by multiple nonconditional logistic regression method.

RESULTS

Family history (OR = 3.6) was the most important risk factor for lumbar disc protrusion in this study, followed by lumbar load (OR = 2.1), hard-working (OR = 1.8), and time urgency (OR = 1.1). Additionally, physical exercises (OR = 0.5) and bed characteristics (OR = 0.4) appeared to be the protective factors for lumbar disc protrusion. After stratified by age, family history (OR = 14.5), occupational character (OR = 5.2), and physical exercises (OR = 0.2) stronger association with lumbar disc protrusion was seen in subjects younger than 30 years. In subjects from 30 to 55 years, family history (OR = 5.1), lumbar load (OR = 1.91), hard-working (1.9), physical exercises (OR = 0.5), time urgency (OR = 1. 3), bed characteristics (OR = 0.4) were significantly important. In subjects older than 55 years, lumbar load (OR = 2.9) and bed characteristics (OR = 0.4) were closely related to lumbar disc protrusion.

CONCLUSION

Family history, lumbar load, hard-working, and time urgency are the major risk factors for lumbar disc herniation, and physical exercises and sleeping on the hard bed might be the protective factors.

Linkage analysis of adult height in a large pedigree from a Dutch genetically isolated population

Despite extensive research of genetic determinants of human adult height, the genes identified up until now allow to predict only a small proportion of the trait's variance. To identify new genes we analyzed 2,486 genotyped and phenotyped individuals in a large pedigree including 23,612 members in 18 generations. The pedigree was derived from a young genetically isolated Dutch population, where genetic heterogeneity is expected to be low and linkage disequilibrium has been shown to be increased. Complex segregation analysis confirmed high heritability of adult height, and suggested mixed model of height inheritance in this population. The estimates of the model parameters obtained from complex segregation analysis were used in parametric linkage analysis, which highlighted three genome-wide significant and additionally at least four suggestive loci involved in height. Significant peaks were located at the chromosomal regions 1p32 (LOD score = 3.35), 2p16 (LOD score = 3.29) and 16q24 (LOD score = 3.94). For the latter region, a strong association signal (FDR q < 0.05) was obtained for 19 SNPs, 17 of them were located in the CDH13 (cadherin 13) gene of which one (rs1035569) explained 1.5% of the total height variance.

Current evidence for a modulation of low back pain by human genetic variants

The manifestation of chronic back pain depends on structural, psychosocial, occupational and genetic influences. Heritability estimates for back pain range from 30% to 45%. Genetic influences are caused by genes affecting intervertebral disc degeneration or the immune response and genes involved in pain perception, signalling and psychological processing. This inter-individual variability which is partly due to genetic differences would require an individualized pain management to prevent the transition from acute to chronic back pain or improve the outcome. The genetic profile may help to define patients at high risk for chronic pain. We summarize genetic factors that (i) impact on intervertebral disc stability, namely Collagen IX, COL9A3, COL11A1, COL11A2, COL1A1, aggrecan (AGAN), cartilage intermediate layer protein, vitamin D receptor, metalloproteinsase-3 (MMP3), MMP9, and thrombospondin-2, (ii) modify inflammation, namely interleukin-1 (IL-1) locus genes and IL-6 and (iii) and pain signalling namely guanine triphosphate (GTP) cyclohydrolase 1, catechol-O-methyltransferase, mu opioid receptor (OPMR1), melanocortin 1 receptor (MC1R), transient receptor potential channel A1 and fatty acid amide hydrolase and analgesic drug metabolism (cytochrome P450 [CYP]2D6, CYP2C9).