CLCN4 and X-linked intellectual disability: Sequence variations in CLCN4 have recently been associated with X-linked intellectual disability, epilepsy, white matter abnormality, and cortical atrophy in humans (Veeramah et al., 2013; Hu et al., 2016; Palmer et al., 2018; Zhou et al., 2018; He et al., 2021; Xu et al., 2021).