Trisomy 21: conference report and 1990 update.

The most relevant data and stimulating ideas presented and discussed at the symposium are briefly summarized. They centered around four major foci: the genotype, the phenotype, the pathogenesis of Down syndrome (DS), and the Down person. The molecular genetic approaches to the isolation of genes encoded by chromosome 21, the definition of a possible "critical region," and the acquisition of further insights on the origin of trisomy 21 were the main topics of the analysis of the genotype. The study of the phenotype concentrated essentially on three complex traits related to the nervous, immune, and hematologic systems, which show great sensitivity to developmental disturbances, with major effects on DS subjects' health and behavior. The difficulties of investigating the pathogenesis of the syndrome were outlined, but the theoretical bases for devising sound and complete experimental approaches were also delineated. Finally, the special attention that in the last decade the medical and sociopsychological sciences gave to Down persons was also underlined, and future developments indicated. DS still remains a challenge to science and medicine; however, from the symposium emerged a less pessimistic view on actual potentialities for a decisive advancement in its basic knowledge.