Is a familial definition of depression both feasible and valid?

On the basis of familial constellations it is possible to separate out most of the unipolar depressive patients that are seen in the hospital. The groups may be called depression spectrum disease, pure depressive disease, and sporadic depressive disease. The sporadic depressive disease group is older at onset and older at index of admission than the other two groups. The depression spectrum disease and pure depressive disease groups are separated by virtue of the fact that there are more episodes of illness in the latter.