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Genetics

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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.

A notable example is cystic fibrosis, a life-threatening lung disease caused by a mutation of the gene CF on the 7th chromosome.

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.

Chromosomes are thread-like structures consisting of DNA that pass on genetic information from one generation to the next.

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.

Genotypes are the genetic codes that make up our DNA, present in all our cells.

Phenotypes are the physical expressions of these genes, such as blue eyes or curly hair. The environment can influence some of our phenotypes.

An example of the difference is the case of a person with phenylketonuria, an inherited disease that can lead to severe brain damage and learning disabilities. A specific gene, the genotype, causes phenylketonuria.

However, if the disease is detected early, the affected person can follow a strict diet not to develop symptoms. The symptoms caused by not following this diet are the phenotype of this disease. As you may see, genotypes are purely biological, while environmental factors can have a profound effect on the phenotype.

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.

Genetics - Key takeaways

  • Schizophrenia is a severe mental illness that causes delusions, hallucinations, and other symptoms. There is evidence that this disease may be genetic.
  • Genes are small pieces of DNA that instruct our cells on how to build our bodies (in the womb) and how to behave.
  • Our genetic instructions themselves can be called genotypes, while how they express themselves physically is known as phenotypes.
  • Our external environment can influence phenotypes.
  • A study by Gottesman et al. shows a 43% concordance rate for schizophrenia in identical twins.

Frequently Asked Questions about Genetics

Schizophrenia can be inherited genetically, although this does not happen every time. Schizophrenia tends to run in families, so if a person has relatives with schizophrenia, there is a higher chance of developing the disorder.

According to a 1991 study by Gottesman, it seems highly unlikely that schizophrenia is an entirely genetic disorder. The rate at which identical twins (who share 100% of DNA) develop the disorder is around 48%. To be considered 100% genetic, this statistic would have to be 100%. As it is not, it is not likely that schizophrenia is an entirely genetic disorder.

Some individuals are more likely to develop schizophrenia due to inheriting certain genetic traits, but it is not a directly inherited disorder.

There isn’t one single gene that causes schizophrenia. Many genes identified contribute to developing schizophrenia, but each gene only raises a person’s risk of developing schizophrenia by a tiny amount.

Final Genetics Quiz

Question

What is a genotype?

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Answer

 A piece of DNA that tells our cells how to behave and build our body in the womb/as we grow.

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What is a genotype?

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A person's genetic makeup.

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Which of the following are genotypes?

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Blue eyes.

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What is a phenotype?


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A phenotype is a way that a gene is expressed, which external factors can affect.

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Which of the following is a phenotype?

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Dyed pink hair.

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Who carried out a study investigating concordance rates in schizophrenia?

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Answer

Gottesman.

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What is a phenotype?

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A phenotype is the physical expression of genes. Phenotypes can be affected by external factors.

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Who found that children whose biological mother had schizophrenia were more likely to develop the disorder, even when adopted by mentally healthy parents?

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Answer

Tienari et al.

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Who argued that schizophrenia wasn't a disease, but instead a result of stress and social pressures?

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Answer

Bateson.

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What is the term for disorders that multiple genetic mutations or abnormalities cause?

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Polygenic disorders.

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What was the concordance rate for monozygotic twins in Gottesman's 1991 study?

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Answer

48%.

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What was the concordance rate for dizygotic twins in Gottesman's 1991 study?

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17%.

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What was the rate of schizophrenia for the general population in Gottesman's 1991 study?


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1%.

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What do concordance rates in monozygotic twins being higher than that of dizygotic twins tell us about schizophrenia?

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They tell us that genes influence schizophrenia, but it is not fully genetic

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Which of the following is a valid criticism of Gottesman (1991)?

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Monozygotic twins are likely to be raised in similar environments, meaning their concordance rate may be due to this instead.

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What percentage of our genetic information comes from our father?

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Answer

50%.

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Why might Bateson's claims that schizophrenia was not a disease be affected by bias?

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Answer

He was against psychiatry.

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