Читать книгу Abnormal Psychology - William J. Ray - Страница 95

In this section, we consider the genetic level of analysis. This discussion includes a historical understanding of the study of genes as well as their structure. You will then learn about the role of DNA, how genes influence behavior, epigenetics, mitochondria, and endophenotypes.

Genes form the blueprint that determines what an organism is to become. Specific genes have been associated with a variety of disorders as will be described throughout this book. However, the original hope of finding a few genes that were involved in particular mental disorders has not panned out. What has become apparent is that there is a complex interaction of genetic and environmental factors involved in mental illness. Just having a gene does not mean that it is active—it turns on or off under a complex set of circumstances.

As the factors involved have become more complicated, there has been a search for particular processes related to psychopathology. For example, there exists a gene (SERT) that is involved in the removal of the neurotransmitter serotonin from the synapse. A variant of the SERT gene has been associated with depression, alcoholism, eating disorders, ADHD, and autism (Serretti, Calati, Mandelli, & De Ronchi, 2006). Likewise, a variant of the gene (DßH), which is associated with the synthesis of norepinephrine from dopamine, is associated with schizophrenia, cocaine-induced paranoia, depression, ADHD, and alcoholism (Cubells & Zabetian, 2004). It is suggested that the lower level of the proteins produced by the DßH gene is associated with a vulnerability to psychotic symptoms.

As researchers discover genes related to specific forms of mental illness, there may be a need to reorganize the manner in which we view mental illness. One study analyzed the genes from 33,332 individuals with a mental disorder in comparison with 27,888 without a disorder (Cross-Disorder Group of the Psychiatric Genomics Consortium, 2013). This research suggests that similar genetic risk factors involved in calcium channel signaling exist for what we have considered to be separate disorders. These five disorders are autism spectrum disorder, schizophrenia, bipolar disorder, major depressive disorder, and ADHD. This study implies that a particular genetic makeup may put some individuals at higher risk for developing a variety of disorders. There is also research that suggests that having certain mental disorders such as schizophrenia may actually protect these individuals from getting certain types of cancer (Tabarés-Seisdedos & Rubenstein, 2013).

There is a complex interaction of genetic and environmental factors involved in mental illness.

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Overall, current genetic research suggests a complicated relationship between genetic conditions and environmental factors. For example, the MAOA gene, which is located on the X chromosome, makes the neurotransmitters serotonin, norepinephrine, and dopamine inactive and is associated with aggression in mice and humans. Caspi and his colleagues (2002) performed a longitudinal study and found that mistreatment as a child influenced some boys differently from others later in adulthood. Those boys who were mistreated in childhood and had a particular form of the MAOA gene were more likely to be violent and engage in a variety of antisocial behaviors as adults, as well as have problems with law enforcement officials. Those without this particular form of the gene did not display antisocial behaviors, even if they had been mistreated as children. Thus, environmental influences in terms of maltreatment modulate the expression of specific genetic structures but not the expression of others.

As researchers studied how genes turn on and off and what factors influence this, the story became even more complicated—the processes that determine which genes turn on and off could themselves be passed on to the next generation. Of course, which factors turn the genes on and off are largely influenced by the environment of the organism. Thus, although the genes themselves could not be influenced by the environment, it was possible for the environment to influence future generations through its changes to those processes that turn genes on and off. This is referred to as epigenetics.

epigenetics: study of the mostly environmental factors that turn genes on and off and are passed on to the next generation