That both deletion and knockdown of GALK failed to mitigate most of the phenotypes studied here, and in fact phenocopied or exacerbated some of them, suggests that galactose, galactitol or other galactose metabolites – or a combination of metabolites and other factors such as oxidative stress (Jumbo-Lucioni et al., 2013) or perturbed glycosylation resulting from altered levels or ratios of UDP-sugars (reviewed in Fridovich-Keil and Walter, 2008) – might underlie the pathophysiology of acute and long-term outcomes in GALT deficiency. This evidence concerns the gene GALK1 and hyperinsulinemic hypoglycemia, familial, 4.