The next several pages are intended as a "Commentary" on the six target articles bundled together as a Special Issue of the "Journal of Cognition and Development"--literature reviews and research reports all intended to "build bridges" between the study of cognitive development in typical and atypical populations.

Most people have 23 pairs of chromosomes; one set from the mother and one from the father. However, nondisjunction errors during meiosis can lead to a case of trisomy, where there are three rather than two chromosomes. Although such events are not uncommon, they are usually lethal, and account for a high proportion of spontaneous abortions. There…

The autistic syndrome is considered in the context of a disorder of brain development. The authors conclude that disruption of developmental loci most probably occurs in the end stages of neuronal development, after migrating neurons have reached their final place in the brain and are elaborating communicative processes. (Author)