The author reviewed data from five studies and found that depressed
patients with a history of depression in a parent or child have more
sibships containing depression than depressed patients without this family
history. Thus, there is a clustering of depressions in certain families.
Sporadic pure depressive disease (PDD), where no depressive illness exists
in a first-degree family member of a depressed proband, is associated with
a later age of onset than familial PDD, where depressive illness does exist
in a first-degree relationship. The possibility exists that familial PDD
and sporadic PDD are autonomous illnesses. The presence of a family history
of depression may be predictive to some extent of a good response to
adequate tricyclic medication or ECT.