In 1 large study of patients with pheochromocytoma and/or paraganglioma, patients with NF1 and MEN2 mutations could be discriminated from those with VHL and SDH mutations in 99% of cases by the relative concentrations of normetanephrine and metanephrine, as all patients with NF1 and MEN2 presented with tumors characterized by increased plasma concentrations of metanephrine, in contrast to patients with VHL and SDH mutations, usually presenting with increases in normetanephrine or methoxytyramine. The gene discussed is NF1; the disease is paraganglioma.