Studies in RTT mouse models, which recapitulate the symptomatology of human RTT, as well as human postmortem studies have revealed that loss of Mecp2 does not result in neuronal degeneration or cell loss (Akbarian, 2003) but rather in abnormalities in the structure and function of brain microcircuits (Shepherd and Katz, 2011). The gene discussed is MECP2; the disease is Rett syndrome.