NRGN and early-onset autosomal dominant Alzheimer disease: Given Nrgn function in synaptogenesis and synaptic plasticity, it is not surprising that it has been related to various human neurological diseases and disorders, which include Alzheimer disease (Chang et al. 1997; Hellwig et al. 2015; Bereczki et al. 2016; Casaletto et al. 2017; Lista and Hampel 2017; Kvartsberg et al. 2019), Parkinson and Parkinsonian disorders (Koob et al. 2014; Selnes et al. 2017), schizophrenia (Giegling et al. 2010; Van Winkel et al. 2010; Gurung and Prata 2015; Wen et al. 2016; Zhang et al. 2019; Jin et al. 2019) and Huntington’s disease (DiFiglia 1990).