A disorder where too much insulin causes low blood sugar in infants. Prompt treatment is needed to avoid the brain being damaged by repeated periods of low blood sugar. The various types of familial hyperinsulinemic hypoglycemia are distinguished by their genetic origin. HHF4 is due to a mutation in the gene for 3-hydroxyacyl-CoA dehydrogenase on chromosome 4q22-q26. See also Hyperinsulinemic hypoglycemia, familial, 4