Prior to our study, two disease-causing, homozygous AP1S1 variants in seven patients were reported; these variants, c.364dupG and c.301-2A>G, caused premature stop codons and AP1S1 mRNA decay (Martinelli et al. 2013; Montpetit et al. 2008), and were identified in each case with the full clinical pattern of MEDNIK syndrome, except for the variable presence of a peripheral neuropathy. This evidence concerns the gene AP1S1 and MEDNIK syndrome.