Recent technology using a fluorescent protein tagged to a synaptic marker (e.g. AAV-DIO-mRuby-T2A-synaptophysin-eGFP, [Knowland et al., 2017]) or the trans-synaptic infection of AAV1-Cre (Zingg et al., 2017) would overcome this limitation. The gene discussed is SYP; the disease is infection.