We found that below 1μM of HF treatment, none of the two specific UPR target genes (edem1 and grp78) were up-regulated, suggesting that for up to 100 nM of HF, the upregulations observed for ddit3, asns, and xbp1 mainly rely on the activation of the GCN2 pathway but not on the PERK axis. Here, EIF2AK4 is linked to hydrops fetalis.