SLC39A4 and acrodermatitis enteropathica: Furthermore, the expression of ZIP4 is regulated through proteolytic processes that respond to changes in the zinc concentration within enterocytes.177,178 Mutations in ZIP4 can lead to acrodermatitis enteropathica, a rare autosomal recessive metabolic disorder characterized by ZD, commonly observed in infants.179,180 In the case of ZD, ZIP4 is translocated to the apical surface of the small intestinal epithelial cells.