Objective:To determine whether a unique human T-lymphotropic virus type I (HTLV-I) transmission cohort containing multiple disease manifestations could be used to establish a relationship betweentaxgene sequence and HTLV disease expression.Methods:DNA was extracted from the peripheral blood mononuclear cells (PBMC) of the HTLV-infected persons in the cohort. A 1.1-kb fragment oftaxwas amplified by polymerase chain reaction (PCR) and cloned. Six to 12 individual clones were sequenced per person.Results:Comparison to a reference ATK strain showed numerous differences; however, consensustaxsequences from all persons within the transmission cohort were identical. Intraperson variation was 0.1% to 0.3%.Taxsequences from the index case did not differ from those obtained from a transfusion recipient who developed tropical spastic paraparesis/HTLV-I-associated myelopathy (TSP/HAM).Taxsequences from the same index case did not differ from sequences obtained from the asymptomatic or ATL phases of a second recipient.Conclusions:In this cohort there did not appear to betaxgenotypes associated with specific disease manifestations of HTLV infection.Journal of Human Virology 1999;2:308-314 © Lippincott Williams & Wilkins, Inc.