3MGA is not a discriminative feature but a minor finding in the biochemical phenotype of ECHS1 deficiency; however, in combination with increased excretion of erythro‐2,3‐dihydroxy‐2‐methylbutyrate, elevated plasma lactate and normal acylcarnitine profile in a patient with LS should prompt consideration of SCEH deficiency. The gene discussed is ECHS1; the disease is hyperinsulinemic hypoglycemia, familial, 4.