ARC and Hyperammonemia: In search for further gene transcripts which might be affected by hyperammonemia and involved in histamine‐ or dopamine‐mediated synaptic plasticity, we screened for relevant genes in the cortical transcriptome of HE patients postmortem. We found similarities between Australian and European cohorts in the reduced expression of ARC (activity‐regulated cytoskeleton‐association protein), EGR1 (early growth response protein 1), and EGR4 but did not detect changes in HNMT (histamine N‐methyltransferase: a correlate of histaminergic activity46).