[Development and the developmental disorders of human brain. I. Early development of the cerebrum]

The recent discovery of many genes that regulate brain development is revolutionizing our knowledge of neuroembryology and, moreover, our understanding of how gene defects cause human birth defects. The first 8 weeks of the development of the cerebrum can be subdivided into 23 stages, with early development of mostly the spinal cord and the brain stem. Regionalization of the brain has been related to genes that play a part in it. A characteristic developmental disorder for this early phase in the development of the forebrain is holoprosencephaly, a brain patterning disorder. Numerous genes play a part in its occurrence; abnormal function of signal factors as well as of transcription factors may lead to holoprosencephaly.