HMGCL and hyperinsulinemic hypoglycemia, familial, 4: Its elevation is a strong indicator of organic acidemias in the leucine pathway, such as 3-methylcrotonyl-CoA carboxylase (3MCC) deficiency, 3-hydroxymethyl-3-methylglutaryl-coenzyme A lyase (HMG-CoA lyase) deficiency, β-ketothiolase deficiency, and multiple carboxylase deficiency (MCD).