AP1S1 and ichthyosis: The MEDNIK syndrome (an acronym for mental retardation, enteropathy, deafness, neuropathy, ichthyosis, keratodermia), characterized by overlapping symptoms of Wilson and Menkes disease, is caused by a pathogenic variant in the AP1S1 gene that encodes for the σ1A subunit of AP-1 (Martinelli and Dionisi-Vici, 2014).