[HTLV-I tax gene on the etiological identification of tropical spastic paraparesis. A clinical, serological and polymerase chain reaction (PCR) study in 72 patients].

BACKGROUND

Tropical spastic paraparesis (TSP) is an endemic disease in Chile. In most countries, only 50% of patients are seropositive to HTLV-I. However, new studies suggest that seronegative TSP is also associated with HTLV-I.

AIM

To describe clinical and virological features of seronegative patients with TSP.

PATIENTS AND METHODS

Seventy two Chilean patients with TSP, studied by clinical, radiological and laboratory methods during 1998, are reported. The determination of antibodies to HTLV-I was accomplished by ELISA, immunofluorescence and Western-blot analysis. Polymerase chain reaction for tax and 5'Ltr genes was made using primers SK 43-44, LTR1 and LTR6.

RESULTS

Thirty one patients were HTLV-I positive and 41 were negative. No clinical, radiological or laboratory differences were observed between both groups. In seropositive patients, tax and 5'ltr viral gene sequences of the HTLV-I provirus were detected in DNA of peripheral blood mononuclear cells. In seronegative cases, sequences of tax gene were detected, exclusively, in 18 of 41 patients.

CONCLUSIONS

These results confirm an association with HTLV-I infection in 43.9% of the TSP seronegative patients. These findings support the hypothesis that a defective provirus infects peripheral blood mononuclear cells in seronegative cases of TSP. The importance tax gene in the diagnosis of the TSP is also emphasized.