Search for a schizophrenia susceptibility gene on chromosome 13

Linkage and associated studies of schizophrenia

Genetic epidemiology has provided consistent evidence over many years that schizophrenia has a genetic component, and that this genetic component is complex, polygenic, and involves epistatic interaction between loci. Molecular genetics studies have, however, so far failed to identify any DNA variant that can be demonstrated to contribute to either liability to schizophrenia or to any identifiable part of the underlying pathology. Replication studies of positive findings have been difficult to interpret for a variety of reasons. First, few have reproduced the initial findings, which may be due either to random variation between two samples in the genetic inputs involved, or to a lack of power to replicate an effect at a given alpha level. Where positive data have been found in replication studies, the positioning of the locus has been unreliable, leading no closer to positional cloning of genes involved. However, an assessment of all the linkage studies performed over the past ten years does suggest a number of regions where positive results are found numerous times. These include regions on chromosomes 1, 2, 4, 5, 6, 7, 8, 9, 10, 13, 15, 18, 22 and the X. All of these data are critically reviewed and their locations compared. Reasons for the difficulty in obtaining consistent results and possible strategies for overcoming them are discussed. Am. J. Med. Genet. (Semin. Med. Genet.) 97:23-44, 2000.

The human genome project and its impact on psychiatry

There has been substantial evidence for more than three decades that the major psychiatric illnesses such as schizophrenia, bipolar disorder, autism, and alcoholism have a strong genetic basis. During the past 15 years considerable effort has been expended in trying to establish the genetic loci associated with susceptibility to these and other mental disorders using principally linkage analysis. Despite this, only a handful of specific genes have been identified, and it is now generally recognized that further advances along these lines will require the analysis of literally hundreds of affected individuals and their families. Fortunately, the emergence in the past three years of a number of new approaches and more effective tools has given new hope to those engaged in the search for the underlying genetic and environmental factors involved in causing these illnesses, which collectively are among the most serious in all societies. Chief among these new tools is the availability of the entire human genome sequence and the prospect that within the next several years the entire complement of human genes will be known and the functions of most of their protein products elucidated. In the meantime the search for susceptibility loci is being facilitated by the availability of single nucleotide polymorphisms (SNPs) and by the beginning of haplotype mapping, which tracks the distribution of clusters of SNPs that segregate as a group. Together with high throughput DNA sequencing, microarrays for whole genome scanning, advances in proteomics, and the development of more sophisticated computer programs for analyzing sequence and association data, these advances hold promise of greatly accelerating the search for the genetic basis of most mental illnesses while, at the same time, providing molecular targets for the development of new and more effective therapies.