Genetics

A gene is a small part of DNA that contains the instructions for how a person’s cells behave and how their body functions. Our genes have the instructions for everything that makes us who we are, from our skin colour to the patterns on our fingerprints, and can also determine essential aspects of our health. We receive these genetic blueprints from our parents, half from our mother and half from our father at conception.

Can genetics cause mental illness?

Genetic mutations can cause many health problems.

If mutations of a single gene can cause the malfunction of the many glands and organs affected by cystic fibrosis, a similarly minute change in another gene can affect an organ as complicated as our brain.

Types of genetic mutations

• Single gene inheritance disorders (monogenetic) – Mutation, alteration, or deletion of a single gene causes monogenetic disorders.
• Multifactorial gene inheritance disorders – A combination of environmental factors and mutation, alteration, or deletion of one or more genes causes polygenic disorders.
• Chromosomal abnormalities – a missing or additional chromosome, or alteration of a chromosome structure.

Genotypes and phenotypes in genetics

We can talk about our genes and how they are expressed using the terms’ genotype’ and ‘phenotype’. These similar terms can help us describe how genes can cause disease, and you will find it helpful to define them in your exam.

What are the genotypes and phenotypes in schizophrenia?

In terms of schizophrenia, genotypes are the genes associated with schizophrenia, or which might cause someone to develop the disorder.

Phenotypes are the symptoms of schizophrenia, including negative and positive symptoms. For example, hallucinations or disorganised speech are both phenotypes of schizophrenia.

What genes might cause schizophrenia?

Considering how important our genes are and their impact on disease, it is plausible that genes cause schizophrenia. One well-known theory on the development of schizophrenia is the dopamine hypothesis, which states that too much or too little dopamine (a neurotransmitter in our reward system) in the brain can cause schizophrenia.

Genes such as COMT, DRD4 and AKT1 are all associated with excess dopamine and may be linked to schizophrenia (Benzel et al., 2007). Currently, schizophrenia is considered a polygenic disorder associated with many genes due to its complexity, i.e., the wide range of symptoms and manifestations.

Studies supporting genetics as an explanation of schizophrenia

Let us first look at a few studies that support genetics being a crucial factor in the explanation of schizophrenia.

Gottesman (1991)

Gottesman studied families and the incidence of schizophrenia within those families. He measured concordance rates – the rates at which a family member develops schizophrenia when another member already has it. The study was conducted in a London hospital with an equal number of male and female participants between the ages of 16 and 64. The rates it found were as follows:

• Identical/monozygotic twins: 48%

• Non-identical/dizygotic twins: 17%

• Siblings: 9%

• General population: 1%

The fact that there is such a large difference between concordance rates in identical twins (sharing 100% of DNA) and non-identical twins (sharing 50% of DNA) shows that there must be a genetic influence on the likelihood of someone having schizophrenia.Although this argues for the genetic explanation of schizophrenia, it is important to note that the concordance rate for identical twins who share 100% of their DNA is not 100%, which means that there must be some other environmental factor that influences the development of schizophrenia.

Tienari et al. (2004)

Tienari et al. found that children whose birth mother had schizophrenia had a higher risk of developing the disease, even if they were adopted from an early age into a family where no one had the disease. This finding supports the notion that there must be a genetic link to the development of schizophrenia.

Refuting the role of genetics in schizophrenia

As with all research, we can also find the refutation to the role of genetics in schizophrenia across several studies, which we will look into below.

Bateson et al. (1956)

Bateson et al. (1956) proposed the ‘double bind’ theory, which states that the environment in the parental home can cause people to develop schizophrenia. The theory states that a child can become confused if they receive contradictory messages (e.g. a parent says something that seems friendly but at the same time shows angry or dismissive body language). By the time they get to an age where they can recognise the ‘double bind’ as such, they have already internalised this confusion. Furthermore, this communication style can prevent children from developing a consistent and coherent perception of reality and the world around them. Bateson suggests that these problems manifest as schizophrenic symptoms such as paranoia, disorganised speech, and delusions.

Limitations of Bateson’s (1956) double-bind theory

It is perhaps worth noting that Bateson was known for his dismissive attitude towards psychiatry, although he was a psychologist and did not believe that schizophrenia was a disease. Instead, he believed that schizophrenia resulted from stress and social pressure in a person’s life. This may indicate some bias in his theory and its rejection of biological explanations such as genetics.

Brown et al. (1959)

Brown et al. (1959) is a study that supports the theory that high levels of negative and expressed emotions within a family increase the likelihood of children developing schizophrenia. In this hypothesis, the expressed emotion is a communication style within the family characterised by a generally hostile social environment, excessive emotional involvement, and high levels of criticism.

The study states that this type of home environment is more likely to be responsible for the maintenance and relapse rates of the disorder than the onset. Brown et al. found that individuals who returned to such a home environment after treatment for schizophrenia were more likely to relapse than individuals who returned to a home without this communication style.

This relapse rate was even higher for schizophrenic patients who returned to this type of home and did not receive medication.Schizophrenia is a severe mental illness that causes delusions, hallucinations, and other symptoms.There is evidence that this disease may be genetic.