SLC39A4 and Zinc deficiency: This conclusion is supported by: (i) the disease phenotype of acrodermatitis enteropathica, which involves extreme and potentially lethal zinc deficiency and is caused by, among others, diverse mutations at amino acid position 372 in ZIP4 [43]; (ii) the absence of cellular zinc transport in Leu372Arg and Leu372Pro acrodermatitis mutants; (iii) the finding that the Val372 variant leads to reduced zinc transport at the cellular level; and finally (iv) the conservation of this amino acid position across diverse species (Figure 4).