In summary, we report two siblings with MEDNIK syndrome in whom a homozygous mutation was found in the c.430-1G>A splice site of AP1S1. This mutation leads to the occurrence of splice-3 (i.e., the 3⁣′-end splicing mutation), indicating its possible effect on mRNA production and protein function [16]. This evidence concerns the gene AP1S1 and MEDNIK syndrome.