GF mice exhibit markedly altered behavioural and cognitive phenotypes, in part due to altered expression of brain‐derived neurotrophic factor (BDNF) and NMDARs, implicated in depression (BDNF) and neurogenesis and synaptic plasticity (NMDARs) (Neufeld et al., 2011). The gene discussed is BDNF; the disease is major depressive disorder.