The present report describes a mother and 2 children with leucine-induced hypoglycemia (LIH). Hypoglycemic episodes following high-protein meals first appeared at age 4-7 months. Leucine-stimulation tests triggered marked hyperinsulinism and hypoglycemia in the children and a milder but abnormal response in the mother. To evaluate the therapeutic effects and to study the mechanism of hyperinsulinism in LIH, the leucine test was repeated under treatment with diphenylhydantoin, oxprenolol (a beta-blocker), and diazoxide. Diazoxide abolished hyperinsulinism; diphenylhydantoin did not affect the response to leucine; and oxprenolol, tested in the mother only, increased hyperinsulinism and hypoglycemia. Our results indicate that LIH is an autosomal dominant disorder; LIH may persist into adulthood with milder clinical symptoms and chemical response to leucine; diazoxide is the treatment of choice in LIH. Considering the effects of the three agents on stimulated release of insulin, it is concluded that leucine triggers hyperinsulinism by a mechanism different from that of glucose and beta-adrenergic receptors.
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