CTSD and neuronal ceroid lipofuscinosis: Biallelic mutations of the CTSD gene leading to NCL or NCL‐like disease have been reported in nine studies (Doccini et al., 2016; Fritchie et al., 2009; Hersheson et al., 2014; Meyer et al., 2015; Regensburger et al., 2020; Siintola et al., 2006; Steinfeld et al., 2006; Thottath et al., 2019; Varvagiannis et al., 2018), in which, 12 different mutations were identified from 10 families in total.