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Genetics of Bipolar Disorder

Susanne Bengesser and Eva Reininghaus

The high hereditary factor of Bipolar Disorder has been proven by many twin-, adoption- and family-studies already decades ago. Concordance rates between monozygotic twins are even as high as 40-70%. Children of two affected parents have a lifetime-risk of 50-65% to fall ill with Bipolar Disorder, while children with one affected parent show a risk of 25% to get Bipolar Disorder. Therefore psychiatric genetics is highly important to detect the genetic blueprint of Bipolar Disorder to invent prevention strategies, as well as individualized pharmacotherapy and new medication targets. Interestingly top susceptibility genes belong to the ion channel group, growth hormones, clock genes, neurotransmitter systems, Lithium sensitive pathway and other important groups. A detailed and exciting description is given by the authors within this book. Furthermore basic principles of genetics, gene-environment-interactions and genetic overlaps between psychiatric diseases are described to picture the whole painting of Genetics of Bipolar Disorder.

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4. Genetic overlaps between psychiatric diseases

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Since Kraepelin divided affective disorders and schizophrenia in two distinct categories nobody has ever questioned the Kraepelinian dichotomy, although both diseases share at least psychosis. Nowadays, however, genetic discoveries argue that bipolar affective disorder and schizophrenia are more related than assumed before. To determine whether boundaries between schizophrenia and bipolar disorder are blurred one must elucidate the genes, which are shared by both diseases [Lin et al. 2008]. 4.1 Overlaps between mood disorders and schizophrenia 4.1.1 Schizophrenia Already over 150 years ago Kraepelin described schizophrenia as “dementia praecox “[Peters et al. 2006]. Then Eugen Bleuler (1857-1939) coined the term schizophrenia. Kurt Schneider, a German psychiatrist and a pupil of Karl Jas- pers, divided the symptoms into first and second rank. First rank symptoms comprised of audible thoughts, arguing voices, commenting voices, experience of influences playing on the body, thought withdrawal, thought insertion, thought diffusion (also called thought broadcast) and delusional perception. Modern classifications include fundamental symptoms of Bleuler and Schneider. Since some decades the symptomatology distinguishes between positive and negative symptoms. Positive symptoms are delusions and hallucinations, while negative ones are flattening of affect, poor planning, more generally expressed, lowering of energetic potential [Tölle 2008]. The etiology and pathophysiology of schizophre- nia is not exactly known, but it is for sure multifactorial. A combination of neurobi- ochemical, neuroanatomic and genetic alterations lead to disease. The classical “dopamine hypothesis” states that schizophrenia is based on “dopaminergic hyperactivity“. But there are also imbalances in the serotonin-, glutamate- and 116 GABA-systems [Kapfhammer...

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