Inspection of the mean anti-Tax antibodies among the different HTLV-I infected groups showed that the 40 HAM/TSP patients had a mean anti-Tax antibody titer of 518,849 LU that was close to twice the mean value of 282,900 LU for the asymptomatic HTLV-I carriers. This evidence concerns the gene CNTN2 and tropical spastic paraparesis.