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The association between human T cell lymphotropic virus (HTLV) type I tax variation and disease outcome was studied. The tax gene was sequenced in 61 patients with HTLV-I—associated myelopathy/tropical spastic paraparesis (HAM/TSP), 55 patients with adult T cell leukemia, and 62 healthy carriers (HCs). Phylogenetic analysis revealed 2 tax gene subgroups that are related on the basis of the long terminal repeat sequence. Further analysis using restriction fragment length polymorphism in 192 patients with HAM/TSP and 200 HCs revealed a higher incidence of 1 tax subgroup (taxA) in HAM/TSP. taxA was present in 30 (15.5%) of 192 patients with HAM/TSP and in 14 (7%) of 200 HCs. The difference was significant (χ2 = 6.47; P = .014; odds ratio, 2.46; 95% confidence interval, 1.26–4.80). This effect was independent of HLA-A*02, which has been reported to prevent HAM/TSP development. These findings suggest that both host genetic factors and HTLV-I subgroup are associated with different risks for development of HAM/TSP.
Furukawa et al. (Wed,) studied this question.