L1CAM and Cognitive impairment: For instance, X-linked hydrocephalus (XLH), which can result from mutations in the L1 cell adhesion molecule (L1cam) gene in mice (Dahme et al., 1997; Demyanenko et al., 1999), rats (Emmert et al., 2019) and humans (Adle-Biassette et al., 2013; Dahme et al., 1997; Rosenthal et al., 1992), varies in severity from hydrocephalus with multiple structural abnormalities and prenatal death to a milder phenotype with cognitive impairment or isolated symptoms even within the same family (Fryns et al., 1991; Serville et al., 1992).