3-hydroxyisobutyryl-CoA hydrolase (HIBCH) and short-chain enoyl-CoA hydratase (ECHS1 or crotonase) deficiencies are rare disorders in valine catabolism. HIBCH is responsible for the conversion of 3-OH-isobutyryl-CoA to 3-OH-isobutyric acid and its deficiency results in the buildup of 3-OH-isobutyric acid, which conjugates with free carnitine to 3-OH-isobutyryl carnitine (C4OH), which can be detected in acylcarnitine analysis. The ECHS1 enzyme is reversible which results in the buildup of methacrylyl-CoA, a highly reactive compound which conjugates with thiol groups and results in the accumulation of several toxic intermediates, including S-(2-carboxypropyl)-cysteamine, S-(2-carboxypropyl)-cysteine (SCPC) and its carnitine ester (SCPC-C)
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