Genetic Explanation of Schizophrenia

The genetic explanation proposes that schizophrenia develops due to the presence of certain genes or combinations of genes. This theory is supported by twin studies and adoption studies, which examine concordance rates - the likelihood of developing schizophrenia if a relative has the disorder.

Evidence from Gottesman's 1991 study on inheritance and twin studies shows a clear pattern: the more genes shared with a person who has schizophrenia, the higher the risk of developing the disorder. For example:

• Identical twins have a 48% risk
• Fraternal twins have a 17% risk
• First-degree relatives (parents, siblings, children) have a 13% risk
• Second-degree relatives have a 4-6% risk
• The general population has a 1% risk

Example: If one identical twin has schizophrenia, the other twin has a 48% chance of also developing the disorder, compared to only a 17% chance for fraternal twins.

Highlight: While the genetic link is strong, no concordance rate reaches 100%, indicating that other factors beyond genetics play a role in the development of schizophrenia.

Adoption Studies and Candidate Genes

Adoption studies provide further evidence for the genetic basis of schizophrenia while also highlighting the importance of environmental factors. The Tienari et al. (1994) study compared adopted children of schizophrenic parents with adopted children of non-schizophrenic parents. The results showed:

1. A higher rate of psychoses and severe diagnoses in the offspring of schizophrenic parents
2. The genetic effect was only manifested in the presence of a disturbed family environment
3. The impact of disturbed family relations was strongest when combined with genetic predisposition

These findings support a genetic hypothesis for schizophrenia but also emphasize the interaction between genetic and environmental factors.

Recent genetic research has identified numerous candidate genes associated with schizophrenia:

• A 2014 study by Ripke et al. found 108 distinct locations on the human genome linked to schizophrenia
• These genetic locations were primarily in regulatory regions rather than coding regions
• Geschwind noted that most schizophrenia-linked DNA interacted with genes crucial for brain development

Vocabulary: Heterogeneity - The quality of being diverse in character or content.

Highlight: The genetic basis of schizophrenia is complex, involving multiple genes and variations, which contributes to the heterogeneity of the disorder.

The Dopamine Hypothesis

The dopamine hypothesis is a prominent biological explanation of schizophrenia that focuses on the role of the neurotransmitter dopamine in the brain. This theory proposes that imbalances in dopamine activity contribute to schizophrenia symptoms. The hypothesis identifies two key aspects:

1. Hypodopaminergia: Low dopamine activity in the prefrontal cortex (mesocortical pathway), associated with negative symptoms of schizophrenia.

2. Hyperdopaminergia: Excessive dopamine activity in the mesolimbic pathway, associated with positive symptoms of schizophrenia.

The dopamine hypothesis suggests that these imbalances may be due to:

• Variations in the number of dopamine receptors in different brain areas
• Differences in the sensitivity of dopamine receptors

Vocabulary: Neural correlate - A measurable brain function or state that corresponds with a particular mental state or behavior.

Definition: Positive symptoms are abnormal experiences or behaviors that are present in schizophrenia, such as hallucinations or delusions. Negative symptoms refer to normal behaviors or experiences that are absent or diminished in schizophrenia, such as lack of motivation or social withdrawal.

Highlight: The dopamine hypothesis provides a biological explanation of schizophrenia that links brain chemistry to specific symptoms, offering potential targets for treatment.