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.