Current developments in the understanding of mental retardation. Part I: Biological and phenomenological perspectives.

During the past decade, noteworthy advances have taken place within the field of mental retardation. The application of advanced biological techniques in such areas as molecular genetics and neuroimaging has substantially improved our ability to identify the biological factors that underlie the origin and pathogenesis of an increasing number of mental retardation syndromes. Refined genetic and psychosocial assessments have highlighted the impressive degree of heterogeneity that is present within and across many mental retardation syndromes, stimulating increasing interest and study. This, the first of a two-part review, will focus on recent developments in biological and phenomenological aspects of mental retardation.