Zinc Transporter mutations and human growth

Twenty-four zinc transporter genes control zinc homeostasis in mammals, and mutations in many of these genes have been shown to profoundly affect growth and differentiation in mouse models and in lower eukaryotes. Our understanding of the genetics of zinc transporters in human growth is a rapidly expanding field. Herein we present a brief overview of our current understanding of mechanisms of zinc homeostasis and the functions of zinc in growth followed by a discussion of three zinc transporters which have recently been shown to play important roles in human health. The pseudoautosomal dominant disease acrodermatitis enteropathica is caused by the loss of function of one or both Zip4 (Slc39a4) alleles which leads to diminished uptake of dietary zinc, increased sensitivity to zinc deficiency, and severe growth retardation unless treated by the continual administration of exogenous zinc. Spondylocheiro dysplastic form of Ehlers-Danlos syndrome is an autosomal recessive disease caused by homozygous loss-of-function mutations in the Zip13 (Slc39a13) gene. This leads to altered intracellular zinc distribution, impaired development, and diminished collagen crosslinking by osteoblasts, chondrocytes, odontoblasts, and dermal fibroblasts which results in growth retardation and stunting, among a plethora of other symptoms. This disease cannot be ameliorated by the lifelong administration of exogenous zinc. Transient neonatal zinc deficiency is a very rare autosomal dominant disease that can be caused by a mutation in one ZnT2 (Slc30a2) allele. This mutation leads to diminished zinc content in breast milk during the period soon after birth which causes transient growth retardation and dermatitis in the nursing child. This disorder can be ameliorated by the administration of exogenous zinc to the baby until weaning. Zinc transporter knockout mouse models suggest that in the future other members of the Zip and ZnT gene families will be found to play important roles in human growth.