CHROMOSOME-ABNORMALITIES IN HUMAN-BEINGS

Constitutional chromosomal abnormalities are an important cause of mis carriage, infertility, congenital anomalies and mental retardation in humans. Most human constitutional chromosomal imbalance results from a neuploidy, a condition that appears to be much more frequent in humans than in any other species studied. Chromosomal rearrangements and seg mental deletions and duplications also occur in humans, but much less often, Although treatment of human somatic cells with some environment al agents produces chromosomal damage, no measurable increase in the f requency of constitutional chromosomal abnormalities has been unequivo cally demonstrated among the children of parents exposed to any agent, Recent work has provided insight into a variety of mechanisms by whic h chromosomal abnormalities can arise during gametogenesis and early e mbryogenesis. Mechanisms have also been recognized that can correct or partially compensate for chromosomal imbalance, sometimes permitting survival of conceptuses that would otherwise be lost early in gestatio n. This improved understanding can be used to refine future studies of the cytogenetic effects of environmental exposures. (C) 1997 Elsevier Science B.V.