Short-chain 3-hydroxyacyl-coenzyme A dehydrogenase hyperinsulinism (SCHAD-HI), caused by homozygous mutations in the hydroxyacyl-coenzyme A dehydrogenase (HADH) gene that lead to deficient SCHAD activity, is a rare CHI subtype accounting for less than 1% of all cases. The gene discussed is HADH; the disease is hyperinsulinism.