The brain in Down syndrome.

Down syndrome (trisomy 21) is a genetic disease with developmental brain abnormalities resulting in early mental retardation and precocious, age dependent Alzheimer-type neurodegeneration. We tried to discuss the role of neurodevelopmental abnormalities in connection with aberrant expression of genes on chromosome 21 including amyloid precursor protein (APP), CuZn superoxide dismutase (SOD1) and glial-derived S100 beta protein for neurodegeneration in DS. In this model, alterations in developmental pathways due to aberrant gene expression can impair cellular homeostasis and predispose to neurodegeneration of certain brain regions and types of nerve cells, involving cholinergic, serotonergic and catecholaminergic transmission, by shifting balance toward a pro-apoptotic state.