Biological Models of Addiction

Introduction

A long-held assumption in the addiction treatment field is that genetic factors can increase one’s likelihood of developing a substance use disorder (SUD). In other words, alcoholism and drug dependencies tend to “run in families.’’ It’s important to consider that other mental health and medical conditions are also known to have heritability risk factors, such as particular types of cancer or essential hypertension (high blood pressure). For example, schizophrenia is about 50% heritable, while autism is about 70% heritable. Interestingly, there is a great deal of overlap in the genes involved in several distinct mental disorders such as schizophrenia, bipolar disorder, ADHD and depression (Winerman, 2019).Therefore, just as one inherits particular traits from one’s biological parents (e.g. eye and hair color, height, weight, athletic, musical or artistic talents), one can also inherit predispositions to develop a substance use disorder and perhaps even process addictions like gambling disorders.

Although there are several caveats to these genetic theories of addiction, the general consensus is that, for many individuals, his or her substance use disorder might best explained by genetics. One such caveat is that if substance use disorders are indeed inherited, what exactly is inherited that might predispose a person to becoming addicted? Are there differences in one’s basic physiology that are somehow inherited from parents or grandparents? Also, although there has been a great deal of research which examined the possibility of there being an “addictive personality” that pre-determines whether one develops a SUD, the majority of research has focused on inherited physical characteristics (e.g. variations in how alcohol is metabolized or broken down in the body, or depletions in particular neurotransmitters such as dopamine).

Suffice to say, genetic and other biomedical models of addiction are truly etiological models because their main contention is that genetics will determine whether one becomes addicted to alcohol or drugs. Therefore, it’s important to keep in mind, that when we consider the Nature—Nurture controversy, that the biomedical models clearly fall under the “Nature” side of the debate because physical predisposing traits are thought to be internal and therefore are not considered part of environmental (i.e. Nurture) influences.

It’s also important to point out that the biological models that we will be presenting are synonymous with the disease model in that they put forth the notion that similar to how diseases such as cancer, cardiac conditions and sickle cell anemia are thought to be inherited, so too are SUDs. The disease model is also synonymous with the Minnesota Model, which emphasizes the use of the 12 Steps of Alcoholics Anonymous/Narcotics Anonymous as part of the standard treatment protocol. The majority of 28-day inpatient programs for SUD operate on the basis of the Minnesota Model. These include well-known programs such as Hazelden in Minnesota and the Betty Ford Center in Palm Springs, California.

In this chapter, we will also be exploring other biological factors that may help to explain the etiology of substance use disorders. With the advent of advanced neurological imaging techniques like CT scans and PET scans, neuroscientists are better able to look “inside the brain” in order to see how it responds to alcohol and other mood-altering substances. We will therefore be discussing the role of neurotransmitters and particular hormonal imbalances as possible causes of substance use disorders.

Key Terms

concordance rate: the probability or likelihood that twins or two family members will have the same trait of characteristic based on genetic inheritance.

monozygotic twins: also referred to as “identical twins,” occurs when the male sperm fertilizes one egg (or zygote) of the mother. Monozygotic twins have the exact same DNA.

dizygotic twins: also referred to as “fraternal twins,” occurs when male sperm fertilizes two separate eggs of the mother. Dizygotic twins do not have the exact same DNA.

phenotype: the observable physical and biochemical characteristics of an individual, determined both by genetic make-up and environmental influences.

genotype: the genetic make-up of an individual organism (as distinguished from their physical appearance.The genetic constitution of an individual.

genetic marker, refers to a particular gene or DNA sequence that can be used to identify a particular genetic trait which can be traced back through one’s pedigree.

genetic predisposition: an inheritable characteristic, such as the risk of acquiring a disease like alcoholism or Huntington’s Disease.

Human Genome Project: an international human genetic research project conducted between 1990 and 2003, which determined the base pair sequences in human DNA with the purpose of storing this information in computer databases.

genetic variants: each gene pool contains pairs of DNA pairs. The variations occur both within and among members of a population. Genetic variation is brought about through mutation which then produces a permanent change in the chemical structure of a chromosome.

allele: an alternate or abnormal form of a gene.

alcogene: a specific gene which genetically transmits alcohol use disorders to offspring (e.g. sons and daughters).

CT scan: also known as a computed tomography scan (and formerly known as computerized axial tomography scans or CAT scans), makes use of many computer-generated X-ray measurements taken from many cross-sectional images to produce cross-sectional images of bones, organs and other tissue.

PET scans: also known as positron emission tomography, makes use of radioactive dyes to observe metabolic processes within the body. Three-dimensional computer-generated images are then produced which allows for detection of diseases and metabolism (e.g. brain activity).

evoked potentials: a technique used to measure electrical activity in the brain in response to specific stimulation (e.g. a flashing light) of specific sensory nerve pathways.

epigenetics: modifications that regulate the activity of DNA, involving RNA as “messengers” that determine how genes are expressed.