Human neural stem cells: a new tool for studying cortical development in Down's syndrome.

The clinical characteristics of Down's syndrome (DS), or trisomy 21, are caused by errors that occur during development. In addition to mental retardation, DS individuals have craniofacial abnormalities, clinical defects of the heart, gut and immune system, as well as predisposition to certain diseases, such as leukemias and Alzheimer's disease. To explain the developmental mechanisms that cause these traits, it is necessary to look at how developmental processes in DS compare to normal development. The neurological characteristics of DS are established during the prenatal and early postnatal period in humans, when the bulk of brain development occurs. Mouse models of DS have provided a useful way of studying DS neural development. However, there are clearly significant differences between rodent and human biology that may not be reflected in mouse models. Recent advances in stem cell biology now allow the generation of human neural tissue in the culture dish (Ostenfeld & Svendsen 2003). Stem cells offer a novel model system to study alterations in neuron development in developmental disorders such as DS.