Adult T-cell leukemia with cyclic neutropenia in a seronegative patient carrying only the tax gene of HTLV-I

Human T-Lymphotropic virus type 1 infection in absence of tax gene: A challenge for molecular diagnosis

This is the first report of HTLV-1 infection without detectable tax gene. Even though the tax gene of HTLV-1 presents high genetic stability, in the case presented here no sequence of tax was detected by three different and widely used molecular assays targeting several sequences of the gene. Nevertheless, HTLV-1 pol and env genes and LTR region were properly detectable. Several PCRs targeting tax sequences have been developed and largely used for molecular diagnosis of HTLV infection since the tax gene of HTLV-1 is known to be well preserved and intolerant to changes or mutations. In the case reported here, molecular detection of the virus was challenging. HTLV prevalence is complex and in many regions remains unknown. The identification of HTLV-infected individuals is important to determine its actual prevalence and design strategies to reduce viral spread. The finding and communication of HTLV-1 defective-provirus strains is important and necessary to guide the selection of representative target sequences on HTLV genome to design molecular assays, highlighting that different sequences should be combined to ensure adequate diagnosis. The latter is especially relevant in cases when discordant results between serological and molecular assays. This report contributes to the knowledge of the overall molecular epidemiology of HTLV-1 and encourages the need of surveillance of HTLV-1 "missed tax gene profiles" and the evaluation of the impact of these defective viral variants on molecular diagnosis and human health.

First Description of Seronegative HTLV-1 Carriers in Argentina

In some areas of Argentina endemic for human T-lymphotropic virus type 1 (HTLV-1), tropical spastic paraparesis is frequent in subjects who lack antibodies against the virus; however, the relevance of this seronegative status in the country has not been investigated. In neighboring countries, HTLV-1 seronegative status has been described in patients with different diseases; however, data regarding features of seronegative HTLV-1 carriers are scarce. We investigated the seronegative status in 124 relatives of 28 HTLV-1 infected subjects from an endemic area in Northwest Argentina. Blood samples and clinical/epidemiological data were collected. Human T-lymphotropic virus type 1 infection was diagnosed by serology and long terminal repeat (LTR) sequence, env and tax gene detection. IgG anti-Tax HTLV-1 antibody, tax gene sequence, and DNA proviral load were also evaluated. Seventy-five percent of the 124 relatives were negative for HTLV-1/2 antibodies; 35.5% were also negative by molecular assays and 64.5% were negative for HTLV-1 LTR and env sequences, but positive for two sequences of HTLV-1 tax gene. Also, 35.7% of these subjects had IgG anti-Tax antibodies. The seronegative HTLV-1 status was significantly associated with male gender, youth, and sensory symptoms/autonomic nervous system dysfunction. High rates of seronegative symptomatic and asymptomatic HTLV-1 carriers in Argentina are described. The evidence highlights that HTLV-1 prevalence may be underestimated worldwide. Larger cohort studies are required to assess disease outcome in these seronegative subjects. Also, the findings emphasize the limitations of ongoing screening assays for diagnosis and blood safety. Therefore, algorithms for HTLV-1 diagnosis should include not only serological but also molecular assays.