In mice, overexpression of Tat results in CNS damage and cognitive deficits.24,36 In patients, it has been shown that high levels of Tat antibodies in the cerebral spinal fluid inversely correlate with dementia severity, suggesting that high antibody levels protect against Tat toxicity by sequestering Tat function.3 However, the presence of antibodies against Tat only serves as a proxy estimate.3,6,58 Although direct assessments of Tat have occasionally been made,32 routine measurements would be extremely useful to more accurately assess the role of Tat in the neuropathogenesis of HIV-SN. The gene discussed is TAT; the disease is dementia.