Functional characterization of a novel ZIP8 variant causing impaired manganese homeostasis and congenital disorders of glycosylation.

ZIP8, encoded by SLC39A8, mediates cellular uptake of divalent metal ions, including manganese (Mn). Mutations in SLC39A8 cause a congenital disorder of glycosylation (CDG) associated with Mn deficiency (SLC39A8-CDG). Here, we report a novel case of SLC39A8-CDG harboring a previously unreported mutation (p.F206I) in the transmembrane domain 3 (TMD3). The patient showed markedly low serum Mn levels and abnormal glycosylation. To evaluate the functional consequences of this variant, we generated cells expressing hZIP8-F206I. Mn, cadmium, and zinc uptake levels in cells expressing hZIP8-F206I were approximately half of those in cells expressing wild-type hZIP8. The mutant hZIP8 also showed reduced plasma membrane localization. These findings suggest that this previously unreported mutation in TMD3 significantly impairs ZIP8-mediated metal transport, leading to CDG.