3-Hydroxyisovalerylcarnitine is a carnitine derivative that may serve as a novel biomarker for biotin deficiency in humans, with its concentration increasing in such conditions. Biotin deficiency reduces the activity of biotin-dependent 3-methylcrotonyl-CoA carboxylase, hindering the conversion of 3-methylcrotonyl-CoA into 3-methylglutaconyl-CoA, and impairing the leucine catabolism pathway, resulting in elevated plasma 3-Hydroxyisovalerylcarnitine concentrations [1].