One of the central tenets of developmental psychopathology is the belief that we can
learn more about normal functioning through the study of psychopathology and arrive at a better
understanding of pathological conditions through investigations of normal behavior. Advances in
knowledge from one area will inform us regarding mechanisms at work in the other. A similar
perspective is the driving force behind recent scientific advances in our understanding of certain
developmental disorders. In this paper, molecular findings for four developmental disorders are
reviewed: Prader–Willi syndrome, fragile X syndrome, Williams syndrome, and
lissencephaly. These disorders were chosen for discussion because putative genes for each of
them have been isolated. The ways in which mutations within these genes disrupt normal
cognitive and behavioral functioning are discussed. Although considerable progress has been
achieved in understanding the genetic mechanisms for these illnesses, much more research is
needed to identify the environmental and genetic factors that interact to contribute to the
expression of the more complex behavioral disorders.