Tyramine-conjugation deficit as a trait-marker in endogenous depressive illness.

Patients with endogenous unipolar depressive illness show a highly significant decrease in ability to metabolize an oral load of tyramine to its sulphate conjugate compared with controls and neurotic depressives. As this biochemical lesion persists after clinical recovery and is present in about half the non-depressed first degree relatives of endogenously depressed probands, it is likely that the abnormality is a trait marker for depressive illness. It may thus be useful in practice as a predictor of vulnerability to depressive illness. The tyramine test is superior to the dexamethasone suppression test in both sensitivity to, and specificity for, endogenous depression.