The first pathogenic variant in the AP1S1 gene (c.301-2A > G, splice-site variant) was described in 2008 in four French-Canadian families from Quebec, causing a rare autosomal recessive disease characterized by mental retardation, enteropathy, deafness, neuropathy, ichthyosis, and keratoderma, and named MEDNIK syndrome as an acronym of these clinical features [8, 9]. The gene discussed is AP1S1; the disease is MEDNIK syndrome.