Notably, metabolites commonly used as IEM biomarkers, such as acyl glycines or acyl carnitines, are not annotated to IEM-associated genes in HMDB (e.g., isovalerylglycine, which is a biomarker of 3-methylcrotonyl-CoA carboxylase deficiency, is annotated to the GLYAT family of genes, but not to either of the IEM-associated genes MCCC1 or MCCC2). Here, MCCC2 is linked to hyperinsulinemic hypoglycemia, familial, 4.