RESUMO
BACKGROUND: Symptomatic intervertebral disc degeneration is being recently reported in younger population, questions the basis of its degenerative etiology. Latest evidences show that genetics play a significant role. Collagen IX, an important constituent of disc, is found to be altered in genetically predisposed individuals. Mutations have been reported in COL9A2 and COL9A3 genes, which encode Collagen IX, in Finnish and various other populations. The purpose of the present study is to test the significance of these genes in the Indian population. MATERIALS AND METHODS: One hundred proven cases of intervertebral disc disease (IDD) of various regions of spine were selected for the study, along with matched controls. They were tested for the above mentioned alleles by allelic discrimination method with real-time polymerase chain reaction (PCR) study after isolation of DNA from blood sample. Each blood sample was classified into one of the three types - homozygous, heterozygous, and wild (normal) type allele - separately for COL9A2 and COL9A3 genes. RESULTS: Homozygosity for COL9A2 allelic variation was associated with 100% occurrence of the disease. Heterozygous allele of COL9A2 was significantly higher in the study group (42%) as compared to the control group (17%). In contrast, allelic variation in COL9A3 gene was found to have no significant correlation with disc disease. There was no single patient with homozygous allelic variation for COL9A3, suggesting predominance of COL9A2 variation in the Indian population. CONCLUSION: This candidate gene strategy approach adds considerably to our knowledge of genetic makeup of Indian populations in relation with disc disease. This study highlights importance of COL9A2 gene variation especially of homozygous variety in contrast to COL9A3 variation in causing disc disease in Indian population.
