In light of the SERT gene being a strong candidate gene associated with the severity of PA’s, but not being associated with increase panic symptoms post a CO2 challenge, we assessed baseline anxiety; innate panic responses to a CO2 challenge (as well as cellular responses in anxiety associated neural circuits); and fear conditioned responses in SERT+/− and SERT−/−. The gene discussed is SLC6A4; the disease is Anxiety.