MTOR and fleck corneal dystrophy: A milestone in FCD research was the identification of low-level postzygotic brain-specific mutations disrupting the mTOR pathway and creating a mosaic with a small proportion of variant-carrying cells intermixed with variant-negative cells in postsurgical tissue (Jansen et al., 2015; Lim et al., 2015, 2017; Nakashima et al., 2015; Mirzaa et al., 2016; Moller et al., 2016; D'Gama et al., 2017; Baldassari et al., 2019b).