Nosologic groups. An overview.

A general analysis is made of the concept of nosologic groups. It is concluded that, even when 'artificial',they may prove to be useful research, didactic and differential diagnosis purposes. Nosologic groupings must, however, progress toward the finding of 'phenotypic communities' whose component syndromes share multiple foci of dysmorphogenetically intimate phenotypic overlap. The concepts of syndrome, anomalad, association, combination, dysplasia, phenotypic community and family of diseases are briefly analysed.