The alpha2 type IX collagen tryptophan polymorphism is associated with the severity of disc degeneration in younger patients with herniated nucleus pulposus of the lumbar spine

Tryptophan alleles in COL9A2 (Trp2) and COL9A3 (Trp3) have been linked to lumbar disc diseases in the Finnish population. Although such diseases consist of various pathogenetically different conditions, detailed analysis of each has not been well documented. The aim of this study was to clarify whether the collagen IX tryptophan alleles influence the symptomatic degeneration of the lumbar disc in Japanese patients with herniated nucleus pulposus. We performed a prospective study of 84 patients who underwent lumbar discectomy. The degree of disc degeneration was evaluated by magnetic resonance images in relation to the collagen IX genotype. Twenty patients (21.4%) had the Trp2 allele and no patients had the Trp3 allele. Patients under 40 years with the Trp2 allele showed more severe disc degeneration at the surgical level than did those without the Trp2 allele (odds ratio 6.00, P=0.043). In contrast, patients aged 40 years or over did not show significant association between disc degeneration and collagen IX genotype. Our results suggest that the Trp2 allele is an age-dependent risk factor for the severity of disc degeneration in younger patients with symptomatic herniated nucleus pulposus of the lumbar spine.