Absence of the mutated Trp2 allele but a common polymorphism of the COL9A2 collagen gene is associated with early recurrence after lumbar discectomy in a German population

Intervertebral disc development and disease-related genetic polymorphisms

The intervertebral disc (IVD) comprises a gelatinous inner core (nucleus pulposus; NP) and concentric rings (annulus fibrosus; AF). The NP, an important structure for shock absorption in the vertebrate spinal motion segment, can be traced back to the notochord in ontogenetic lineage. In vertebrates, the notochord undergoes mucinoid changes, and had been considered vestigial until recently. However, observed correlations between IVD degeneration and back pain in humans have renewed interest in the IVD in biomedical fields. Beyond its mechanical contribution to development, the notochord is also an essential signaling center, which coordinates formation of the neural tube and somites. The pertinent signaling molecules, particularly TGF-β and bone morphogenetic proteins (BMPs), continue to play roles in the adult tissues and have been utilized for tissue regeneration. Genetic factors are major determinants of who will develop IVD degeneration and related back pain, and seem to correlate better with disc degeneration and back pain than do external forces on the spine. In summary, the spinal column is a landmark development in evolution. Genes directing the development of the IVD may also contribute to its maintenance, degeneration, and regeneration. Likewise, structural genes as well as genes responsible for maintenance of the structure are related to IVD degeneration. Finally, genes responsible for inflammation may play a dual role in exacerbating degeneration or facilitating repair responses depending on the context.

The role of polymorphisms of genes encoding collagen IX and XI in lumbar disc disease

The intervertebral disc disease (IDD) is one of the most common musculoskeletal disorders. A number of environment and anthropometric risk factors may contribute to it. The recent reports have suggested the importance of genetic factors, especially these which encode collagen types IX and XI. The allelic variants in the collagen IX genes - COL9A2 (Trp2) and COL9A3 (Trp3) have been identified as genetic risk factors for IDD, because they interfere the cross-linking between collagen types II, IX and XI and result in decreased stability of intervertebral discs. Type XI collagen is a minor component of cartilage collagen fibrils, but it is present in the annulus fibrosus and nucleus pulposus of intervertebral discs. Some studies have shown the association between gene COL11A1 polymorphism c.4603C>T and IDD. The frequency of 4603T allele was significantly higher in the patients with IDD than in the healthy controls.

Phenotype variations affect genetic association studies of degenerative disc disease: conclusions of analysis of genetic association of 58 single nucleotide polymorphisms with highly specific phenotypes for disc degeneration in 332 subjects

BACKGROUND CONTEXT

Although the influence of genetics on the process of disc degeneration is well recognized, in recently published studies, there is a wide variation in the race and selection criteria for such study populations. More importantly, the radiographic features of disc degeneration that are selected to represent the disc degeneration phenotype are variable in these studies. The study presented here evaluates the association between single nucleotide polymorphisms (SNPs) of candidate genes and three distinct radiographic features that can be defined as the degenerative disc disease (DDD) phenotype.

PURPOSE

The study objectives were to examine the allelic diversity of 58 SNPs related to 35 candidate genes related to lumbar DDD, to evaluate the association in a hitherto unevaluated ethnic Indian population that represents more than one-sixth of the world population, and to analyze how genetic associations can vary in the same study subjects with the choice of phenotype.

STUDY DESIGN

A cross-sectional, case-control study of an ethnic Indian population was carried out.

METHODS

Fifty-eight SNPs in 35 potential candidate genes were evaluated in 342 subjects and the associations were analyzed against three highly specific markers for DDD, namely disc degeneration by Pfirrmann grading, end-plate damage evaluated by total end-plate damage score, and annular tears evaluated by disc herniations and hyperintense zones. Genotyping of cases and controls was performed on a genome-wide SNP array to identify potential associated disease loci. The results from the genome-wide SNP array were then used to facilitate SNP selection and genotype validation was conducted using Sequenom-based genotyping.

RESULTS

Eleven of the 58 SNPs provided evidence of association with one of the phenotypes. For annular tears, rs1042631 SNP of AGC1 and rs467691 SNP of ADAMTS5 were highly significantly associated (p<.01) and SNPs in NGFB, IL1B, IL18RAP, and MMP10 were also significantly associated (p<.05). The rs4076018 SNP of NGFB was highly significant (p<.01) and rs2292657 SNP of GLI1 was significantly (p<.05) correlated to disc degeneration. For end-plate damage, the rs2252070 SNP of MMP 13 showed a significant association (p<.05). Previously associated genes such as COL 9, SKT, CHST 3, CILP, IGFR, SOXp, BMP, MMP 2-12, ADH2, IL1RN, and COX2 were not significantly associated and new associations (NGFB and GLI1) were identified. The validity of all the associations was found to be phenotype dependent.

CONCLUSIONS

For the first time, genetic associations with DDD have been performed in an Indian population. Apart from identifying new associations, the highlight of the study was that in the same study population with DDD, SNP associations completely changed when different radiographic features were used to define the DDD phenotype. Our study results therefore indicate that standardization of the phenotypes chosen to study the genetics of disc degeneration is essential and should be strongly considered before planning genetic association studies.

Candidate gene association study of magnetic resonance imaging-based hip osteoarthritis (OA): evidence for COL9A2 gene as a common predisposing factor for hip OA and lumbar disc degeneration

OBJECTIVE

To study whether gene variants associated with lumbar disc degeneration (LDD) phenotypes are also associated with hip osteoarthritis (OA).

METHODS

Magnetic resonance imaging (MRI)-based hip OA changes for 345 twins were assessed and 99 single-nucleotide polymorphisms (SNP) were analyzed.

RESULTS

Variants in the COL9A2 (rs7533552, p = 0.0025) and COL10A1 (rs568725, p = 0.002) genes showed association with hip OA.

CONCLUSION

The associating G allele in COL9A2 changes a glutamine to arginine or to tryptophan and may predispose to both hip OA and LDD, making it a candidate for degenerative connective tissue diseases.

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).