ABSTRACT
This chapter aims to indicate what happens to initiate and modify particular causal processes, organic impairments, and their expression in individual children, progressively before, during and just after fetal life. The epidemiological literature is full of debate and dispute as to what is the best definition of mental retardation, but differences in concept underlying or implied by differences in definition are seldom made explicit. Mental retardation incorporates several elements which are difficult to reconcile: low intelligence, genetic potential and expressed learning capacity; poor social adaptation and relative dependency. Epidemiologically, cause is never a single pathway of sequelae, and the social factors in etiology may be more amenable to preventive intervention than the biomedical processes. Etiological or pathological diagnostic entities usually represent specific impairments or groups of impairments. Intellectual impairment, usually severe, is part of a global impairment of cellular structure produced by a chromosome anomaly arising in male or female parent, but how remains mysterious.
