Mutations in the MCOLN1 gene encoding for TRPML1 are responsible for mucolipidosis type IV, which is an autosomal-recessive lysosomal storage disorder characterized by severe psychomotor delay, progressive visual impairment, and an additional stomach parietal cell phenotype of selective vacuolation and constitutive achlorhydria [18]. This evidence concerns the gene MCOLN1 and mucolipidosis type IV.