The Neurodevelopmental Hypothesis of Schizophrenia: Genetic Investigations

Abstract

ABSTRACTTwin, family, and adoption studies indicate that genetic factors play a major role in predisposition to schizophrenia. To date, molecular genetic studies have implicated many different chromosomal locations for the disorder. However, no one site replicates across the majority of investigations. This creates an impasse in the study of schizophrenia genetics, because of the large number of chromosomal sites that require further detailed research. It is difficult to plan to move ahead with expensive and labor-intensive research in an attempt to determine the etiologie genetic factor, when any given site proves to be only weakly positive. Therefore, the use of a hypothesis-driven approach may be cost effective, and may ultimately have more power to detect etiologie genes. Several lines of evidence suggest that a neurodevelopmental defect may play an important role in the etiology of this disorder. Neurodevelopment is a complex process in which genetic and nongenetic factors may interact to create the mature differentiated neuron, with its particular network of synaptic connections. A reasonable chance exists that polymorphisms of the genes that control normal development of the central nervous system (CNS) may produce a slightly altered trajectory of brain development, predisposing individuals to schizophrenia. This assumption has led geneticists to begin to study neurodevelopmental genes in schizophrenia subjects. This article reviews and discusses genetic studies of some developmental genes in schizophrenia. Genetic association and linkage studies of neurotrophic factors (brain-derived neurotrophic factor, or BDNF, and neurotrophin-3, or NT-3), neuronal cell adhesion molecule (NCAM), synapsin, and synaptosome-associated protein with a mass of 25 kd (SNAP-25) have proven to be of most interest.