Abstract
Researchers showed that genetics has a strong influence on individual’s behavior when it comes to addiction. Substance abuse and dependence are disorders that are usually manifested together with some other psychological disorders such as antisocial personality disorder, depression, anxiety and others. Patients who suffer from depression or schizophrenia more often manifest addictive behavior. Explanation for this co-morbidity is found in genetic polymorphism. There are alterations in recorded activity of the brain in individuals who abuse substances. Their brainwaves are abnormal so was the brainwaves of their children, who never tried psychoactive substances. Biology is the basis of the brainwaves and that is what sets vulnerability to addiction. However, there are other points of view that criticize biological perspective and consider it to be a reductionist approach. There are several factors that give its contribution to addictive behavior: environment, genetics and their interference. However, there are a number of proofs which show how significant hereditary factor is.
Introduction
According to contemporary psychology, addiction is the process that comes after use and abuse of psychoactive substance and is characterized by maladaptive behavioral patterns. These behavioral alterations tend to dominate over motivational hierarchy of the affected individual over time. They also contribute to the development of disfunctionality in different spheres of life and cause different physical and psychological disorders. Diagnostic and statistic manual of mental disorders provides information on diagnostic criteria regarding substance abuse and substance dependence. Since this is a complex disorder it is caused by more than one factor. Studies that included examination of addiction in families and twins showed that there is a significant influence of genetics when it comes to this disorder (Dick and Foroud, 2006). Genes that influence on addiction are multiple. The main hypothesis of this paper is that genetic predisposition effects behaviors of future generation, particularly when it comes to addiction.
Methods
It often happens that different etiological factors can lead to same manifestations. This is why scientists performed numerous researches that are very significant due to their diagnostic and therapeutic implications. Great number of researchers investigated whether there are joint genes that are responsible for both addiction and other psychological disorders. Studies examined for the purpose of this research include different subjects, twins, institutionalized individuals who suffer from different psychiatric ailments and cross-national reports. Kendler conducted a study including over 5600 members who were male-male and female-female twin pairs. The data were collected by using personal interview and analyzed by Multimedia twin modeling (Kendler et al, 2003). Kessler and his colleagues collected information from individuals who were uninstitutionalized, 15 to 54 years old and citizens of the United States with the help of interviewers and by using Composite international diagnostic review (Kessler et al, 1994). Merikangas reviewed six different studies and provided cross-national results regarding comorbidity between addiction and psychiatric ailments (Merikangas et al, 1998). Preisig and colleagues researched connection and comorbidity between mood disorders and alcoholism in families with alcohol and anxiety disorders (Preisig et al, 2001). Twin studies, including male twins from which 507 were monozygotic and 575 dizygotic were performed by Tambs and his associates. They used multivariate genetic analysis to analyze data regarding their occupational status, education and intelligence (Tambs et al, 1989). They measured genetic and environmental variance in each of these factors. Young and colleagues performed a study that included 3072 adolescents aged from 12 to 18 years. They gathered data regarding substance use and abuse by using the Composite International Diagnostic Interview- structured interview. They compared substance use and abuse by gender (Young et al., 2002). One more study used in this research paper is physiological study of McGue (2006). This study tried to explain connection between certain types of brainwaves, genes and externalizing ailments. Male adolescent twins who aged 11 and 17 were included in the study. The number of participants was 1196 from which 396 were monozygotic pairs, 202 dyzigotic pairs and 98 % of them were Caucasian. 309 pairs were from one age cohort (11 at the time of their testing) and 289 twin pairs were from another cohort (17 years old). Every participant was assessed according to DSM III with interviews. EEG was recorded while participants were performing specific tasks early in the morning. P3 amplitude ranged from 280 and 600ms. They used standard biometric modeling to estimate genetic predisposition of P3 and external scores including impact of heritage and environment to their covariance (McGue, 2006).
Results
All studies used in this research are coherent with basic hypothesis. Since major depression and schizophrenia are partially hereditary, it can lead to a conclusion that addiction is also caused by genes. This indicates that there are mutual hereditary factors that are responsible for substance use and abuse (Kendler, 2003). Kendler’s twin studies demonstrated that genetic factors in substance abuse and dependence are between 45 to 70 percent.
Kendler performed one of the most significant studies in this field and the results also showed that there is a significant hereditary influence when it comes to alcohol dependence, drug misuse and antisocial disorder. This study once again demonstrated that there are mutual factors responsible for occurrence of these disorders. The correlation between alcohol and drug misuse was higher in monozygotic twins than in twins who shared only half of their genes (Kendler et al, 2003).
Clinical studies showed that half of the patients who abuse substances, at the same time satisfy criteria for major depression. Patients who suffer from schizophrenia are under 4.6 times higher risk from substance abuse when related to healthy population (Kessler et al, 1994).
Merikangas (1998) showed through diferent researches that there is a strong corelation between affective disorders, anxiety disorders, antisocial personality disorder and substance abuse. The results showed that patients with anxiety disorder are more susceptible to substance abuse than other patients. There was a direct corelation between the number of comorbid disorders and increasing levels of severity of substance use disorders (Merikangas et al, 1998). Family studies, performed by Preisig, showed higher levels of alcohol addiction and bipolar disorder co-morbidity, when related to unipolar depression. These studies also showed that family diathesis for mania is significantly associated with substance abuse. His results showed that alcoholism develops after the onset of the disorder, when it comes to bipolar disorders. However, alcohol consumption is noticed earlier in patients suffering from unipolar depression. This showed that alcohol can induce depression, but also that it is comorbid to bipolar affective disorder (Preisig, 2001). Tambs and his colleagues provided evidence that the same risk factors are responsible for both addiction and other mental disorders. Those risk factors include genetic predisposition. Family, adoptive and twin studies confirmed that there is a mutual genetic contribution for addiction and mental disorders. Tambs and associates proved that mutual genetic factors increase the risk for alcohol dependence, anxious disorders and affective disorders. Mentioned studies show that there are evidences that the same genes are responsible for the development of mental disorders and substance abuse and dependence (Tambs et al, 1989). Young provided information showing that substance use is a developmental problem. Substance use is more prevalent in late adolescence than in early period. During the period of adolescence they observed experimenting as more common than abuse. On average 25% of adolescents showed symptoms of substance abuse disorder while 20% were identified as substance dependant. Male subjects were more frequent in substance abuse than women and concluded that gender plays an important role here (Young et al, 2002).
Other important study, McGue’s study, demonstrated that there is measurable correlation between genetic vulnerability and manifestation of addiction. McGue proved that genetic influence on alcohol abuse ranges from 50 to 60 percent in both genders. Research that focused on electric activity of the brain showed that individuals who suffer from some form of addiction manifest abnormalities in EEG. They also found that P3 amplitude and psychological conditions are under the great influence of genetics. Joined appearances of abnormal brainwaves and abuse can be interpreted as potential vulnerability for development of addiction and external psychiatric disorders. As heritage represents the basis for manifested brainwaves, he concluded that genetic is actually an important etiopathogenic factor when it comes to addiction (McGue, 2006).
Discussion
The relationship between addiction and mental disorders is very complex and ambiguous. Psychoactive substances can induce, worsen, decrease or mask symptoms of another psychiatric disorder. This additionally complicates diagnostic process. Among individuals who suffer from some form of addiction the most common co-morbid diagnosis are anxiety disorders, affective disorders, antisocial and other personality disorders. However, Khantzian offered another explanation for this relationship. His understanding of this connection is that a person who suffers from a mental disorder uses psychoactive substances in order to reduce symptoms caused by the primary ailment. This model was suggested in 1985. He thinks that the choice of the substance is not random and that it aims to reduce specific difficulty. For instance, it is noticed that some individuals use heroin to reduce aggressiveness and anger, while cocaine is used to alleviate symptoms of depression, dysphoria and negative syndrome in schizophrenic patients (Khantzian, 1985). Shenk said that the secret with cocaine here is that it elevates mood instantly unlike antidepressants that need to be taken over the period of 2 to 4 weeks in order to cause noticeable changes (Shenk, 1999). Preisig’s study confirms this model showing that patients with bipolar disorder abuse alcohol to diminish their symptoms while those who are unipolar caused their condition by alcohol consumption. Considering these and the fact that neurotransmitters play an important role in regulation of mood it is possible that substance abuse has biological ground. Leshner (1997) assumed that patients with psychiatric disorders turn to substance use and alcohol unconsciously, trying to normalize neurotransmission.
Personality traits are very important when it comes to vulnerability to addictive behavior. It is known that impulsivity, which is manifested as behavioral disinhibition and conducts that are mainly focused on satisfaction of needs without thinking about the consequences of the actions is often found in individuals who suffer from substance abuse and dependence. Another personality trait correlated with these disorders is risk taking. It represents behaviors that include potentially dangerous activities, but also searching for new unknown stimuli. This other aspect of risk taking can be considered as specific trait called novelty seeking. One of new stimuli can be those experienced by substance misuse. Most significant contemporary researches in the field of genetic are those that indicated that there is a connection between dopamine receptor DRD4 and personality trait novelty seeking (Lang, 2005). These studies show that there are shared factors in both personality traits and addiction.
On the other hand, there are researches, such as Heyman, who oppose to biological approach. He refers to studies performed by Peele and Schaler in 2000 and claims that addiction is not a disease. In his critique he explained that there are addicts who are cured without medical assistance which that is not in coherence with biological model. He also proposes a theory that addiction is a matter of choice. He claims that it is something that is learned and not inherited. There are individuals who are under high family risk developing addiction but they never do. Also, prevalence of substance abuse is higher in adolescents than in adults. Heyman claims that these facts prove that addictive behavior is learned (Heyman, 2009).
Conclusion
My research has shown that genes transferred on future generations can in some percentage determine individual’s vulnerability to substance abuse and dependence. However, this does not mean that a person will undoubtedly manifest undesirable behaviors. The realization of genetic predisposition cannot be separated from environmental factors. This is why some of the mentioned studies included the factor of shared environment. All of the researches agree, to some extent, that situational variables are very important and if there is exposure to negative experiences it can represent the trigger for the onset of addictive behavior. Even though twin studies proved that there is a significant relationship between siblings regarding substance abuse and dependence, it is reasonable to ask what the influence of the shared environment is. This is due to the fact that twins share not only genes but environment also. They are exposed to the same family environment which can contribute to development of addiction. Widom and his associates (2007) demonstrated that substance abuse and alcohol dependence among adults who were abused and neglected during their childhood is more prevalent than in the group of adults who were surrounded by caring parents (Widom et al, 2007). Also, children who were maltreated and, at the same time had, genetic predisposition for antisocial disorder and aggressiveness manifested substance abuse disorder in adulthood than those children who were only maltreated but did not have antisocial disorders in family history (Kreek et al., 2005). There are also evidences that indicate that distress and negative events in life play an important role in drug abuse and development of other mental disorders, particularly depression. However, researches showed that from all individuals who experienced mental distress only some of them developed drug related problem and depression. This also proves that some individuals are more vulnerable to distress than other. Never the less , these studies show that there is a specific interaction between heritage and environment and that only one of these factors is not enough to cause addiction (Kreek et al., 2005). Many critiques ask questions about errors in measures or validity of the instruments that are used in the researches. Facts provided by this research represent a fruitful ground for further improvement of instruments and evoke new researches as well.
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