A high-density genome scan detects evidence for a bipolar-disorder susceptibility locus on 13q32 and other potential loci on 1q32 and 18p11.2

Bipolar illness and schizophrenia as oligogenic diseases: implications for the future

As with most complex inheritance diseases, there are at this time no identified susceptibility genes for schizophrenia, bipolar manic-depressive illness, major depression, childhood autism, and other inherited brain disorders whose manifestations are primarily behavioral. Nonetheless, progress has occurred. Genetic epidemiologic research, based on reliable phenotypic definitions, has demonstrated the heritability of many of these disorders. Genetic linkages and associations have been reported and replicated, although there have been inconsistencies between studies, apparently due to the low statistical power of the samples studied to detect small effects genes. Nonreplications of early linkage reports in manic-depressive illness in the 1980s occurred when new cases developed in the same large families in which the linkage was originally reported, and the newly ill persons had the wrong genetic markers in the linkage region. This appears to have resulted from applying inappropriate analytic assumptions of single-gene dominant inheritance of a rare gene, which implied that new cases must arise from the same ancestral gene within the pedigree. When new cases arose in family members not sharing that chromosomal region, the initial linkage report was proved invalid. Under oligogenic inheritance, on the other hand, susceptibility genes are expected to be common, and have a substantial probability of being brought into the pedigree by persons marrying in. Nonspecific psychopathology genes may exist, shared by schizophrenia and bipolar illness, diagnoses which do not co-aggregate in families. The discovery of susceptibility mutations may be expected.

Recent progress in the search for genes for bipolar disorder

Over many decades, much evidence has been accumulated to demonstrate the strong role of genetic factors in bipolar disorder. Recently, genetic studies of bipolar disorder have turned from proving the role of genetics to identifying the specific genes involved. This has been made possible by the development of powerful methods to identify disease genes by their locations on chromosomes, an approach termed positional cloning. Currently, about a dozen regions in the genome have been implicated as the location of susceptibility genes for bipolar disorder. Several of these have been replicated and will likely lead to the identification of novel disease mechanisms. An intriguing development is that a few of these are the same locations implicated in studies of schizophrenia, suggesting a greater genetic relationship between these disorders than had been previously thought. It is hoped that the identification of novel disease genes will lead to a better understanding of the pathophysiology of bipolar disorder and to the development of more effective treatments.

Esquizofrenia

Neste artigo revisamos e resumimos os avanços atuais sobre o mapeamento de genes relacionados à esquizofrenia. Listamos as regiões de interesse identificadas até o momento e discutimos as dúvidas pertinentes, bem como as perspectivas para o sucesso futuro.

Transtorno bipolar

Os resultados de estudos de famílias sugerem que o transtorno bipolar tenha uma base genética. Essa hipótese foi reforçada em estudos de adoção e de gêmeos. A herança do transtorno bipolar é complexa, envolve vários genes, além de apresentar heterogeneidade e interação entre fatores genéticos e não-genéticos. Achados, que já foram replicados, já implicaram os cromossomos 4, 12, 18 e 21, entre outros, na busca por genes de suscetibilidade. Os resultados mais promissores foram obtidos através de estudos de ligação. Por outro lado, os estudos de associação geraram dados interessantes, mas ainda vagos. Os estudos de populações de pacientes homogêneos e a melhor definição do fenótipo deverão contribuir para avanços futuros. A identificação dos genes relacionados ao transtorno bipolar irá permitir o melhor entendimento e tratamento dessa doença.