USP9X and vision disorder: Interestingly, fat facets (the ortholog of Usp9X, involved in endocytosis in the Notch pathway) limits the number of photoreceptors in Drosophila [37], while the human homolog USP9X has been involved in neurodegeneration, mental retardation, epilepsy and autism, as well as in cancer [38], but not yet in visual disorders.