A schizophrenia risk locus alters brain metal transport and plasma glycosylation

A common missense variant (rs13107325 (C->T), A391T) in SLC39A8, a gene encoding a transporter of divalent cations including manganese (Mn), is convincingly associated with schizophrenia and has pleiotropic effects on several additional brain-related phenotypes. Homozygous loss-of-function mutations in SLC39A8 result in undetectable serum Mn and a Congenital Disorder of Glycosylation (CDG) due to the exquisite sensitivity of glycosyltransferases to Mn concentration. Here, we identified Mn-related changes in human carriers of the SLC39A8 missense allele. Analysis of structural brain MRI scans from the UK Biobank showed a dose-dependent change in the ratio of T2w to T1w signal in several brain regions, presumably from altered transport of paramagnetic cations including Mn. We confirmed a specific reduction of serum Mn and showed through comprehensive profiling reduced complexity and branching of the plasma protein N-glycome in both heterozygous and homozygous minor allele carriers. N-glycome profiling of two individuals with SLC39A8-CDG showed similar but more severe alterations in branching that improved with Mn supplementation, suggesting that hypofunction of the common missense variant exists on a spectrum with potential for reversibility. Characterizing the functional impact of this variant may enhance our understanding of schizophrenia pathogenesis and identify novel therapeutic targets and biomarkers of disease.