Schizophrenia
- is a severe mental disorder which affects around 1% of the population. It is characterized by disordered thoughts, delusions, hallucinations, and often bizarre behaviour
- The symptoms of schizophrenia usually appear gradually over time, beginning in late adolescence or early adulthood. The main symptoms can be classed as as being positive, negative or cognitive
Positive symptoms of schizophrenia
are symptoms in schizophrenia that are evident by their presence including delusions, hallucinations or thought disorders.
Delusions - schizophrenia
- are beliefs that are contrary to fact and that are not common in the groups, communities, or family to which the person belongs.
- Individuals can experience delusions of grandeur which are false beliefs in one’s power and importance (e.g., the conviction of having supernatural powers), as well as delusions of control where the person might believe that they are being controlled by others (through something such as an implant in their brain)
Hallucinations - schizophrenia
- are perceptions of stimuli that are not actually present (e.g., hearing sounds that are not present).
- Auditory hallucinations are most common occurring in about 70% of individuals with schizophrenia.
A thought disorder - schizophrenia
- refers to having irrational, disorganized thinking.
- This symptom results in individuals having difficulty arranging their thoughts logically and distinguishing plausible from improbable conclusion
Negative symptoms - schizophrenia
are symptoms in schizophrenia characterized by the absence of behaviours that are normally present such as reduced emotional response, lack of speech, lack of initiative and persistence, anhedonia and social withdrawal.
Cognitive symptoms - schizophrenia
- The cognitive symptoms of schizophrenia may be produced by abnormalities in the brain regions that overlap with those involved in negative symptoms
- For example, the symptoms can involve difficulty sustaining attention, low psychomotor speeds, deficits in learning and memory, poor abstract thinking, and poor problem types
Schizophrenia and genetic factors
• Genetic studies generally suggest that heritability
plays a role in the development of schizophrenia
• There is no single “schizophrenia” gene, rather
research suggests that many genes appear to
increase the likelihood of having schizophrenia
• ‘Schizophrenia genes’ might impart a susceptibility
to develop schizophrenia, but the disease is
triggered by other factors
Schizophrenia and genetic factors - mutations
• A rare mutation of the gene DISC1 (disrupted in schizophrenia
1) appears to be associated with schizophrenia.
• Mutation presence increases the likelihood of schizophrenia by a factor of 50 + increases chance of other conditions such as major depressive disorder.
• DISC1 is involved in regulation of embryonic and adult neurogenesis, neuronal migration during embryonic development, function of postsynaptic density in excitatory neurons and the function of mitochondria.
Schizophrenia and genetic factors - twin and adoption studies
• Twin and adoption studies suggest that schizophrenia is a heritable trait
• Past research assumed that discordance for schizophrenia in monozygotic (identical) twins must
have been due to environmental exposure differences after birth.
• However, the prenatal environment of monozygotic twins is not always identical (i.e. they can have the same or different placenta)
Schizophrenia and genetic factors - twin studies with separate placenta
• The placenta transports nutrients, removes waste products and provides a barrier to toxins that could affect fetal development
• Davis et al. (1995) found the concordance rate for schizophrenia among twins who shared a placenta
was 60%, but only 10.7% for twins who did not share a placenta
Schizophrenia and genetic factors - paternal age
• The effect of paternal age further suggests that genetic mutations impact schizophrenia incidence
• Children of older fathers are more likely to develop
schizophrenia
• Increased likelihood of mutations in chromosomes of cells that produce sperms
Schizophrenia and genetic factors - epigenetics
• Epigenetic factors may predispose people to
schizophrenia
• Epigenetic mechanisms control the expression of genes and are influenced by an individual’s experiences
• Many epigenetic changes are initiated by environmental events such as exposure to toxins, and some epigenetic changes can be transferred to offspring
Epidemiology
is the study of the distribution and causes of
diseases in populations
Epidemiology and schizophrenia
Evidence from epidemiological studies suggests that schizophrenia incidence is associated with: • Season of birth • Viral epidemics • Vitamin D deficiency • Population Density • Prenatal Malnutrition • Substance Abuse • Complications of Birth and Pregnancy
Seasonality effect
People born during the late winter and early spring are more likely to develop schizophrenia
Viral epidemics and the seasonality effect
- Why would the seasonality effect occur?
- Perhaps pregnant women are more likely to contract a viral illness during a critical phase of development if they are pregnant during autumn or winter
- Results in brain development being impacted by a toxin produced by the virus (or antibodies fighting the virus) which crosses the placenta barrier.
Vitamin D deficiency and the seasonality effect
• Cold weather could contribute to the seasonality effect via viral infections, but another factor could be Vitamin D, which plays a role in brain development
• Taking a Vitamin D supplement during the first year of a child’s life was associated with reduced incidence of
schizophrenia among boys
Population density and the seasonality effect
- The seasonality effect is more prevalent in cities compared to rural areas (3 times higher likelihood of developing schizophrenia)
- Could be because viruses are more readily transmitted in high density populations (prenatal influences)
- Furthermore, Pederson and Mortensen (2001) found that up to the age of 15 years, the longer the person lives in a city, the more likely they are to develop schizophrenia (postnatal influences)
Prenatal stress and schizophrenia
- Malnutrition and Stress seem to play a role
- Underweight women are more likely to give birth to babies who later develop schizophrenia
- Prenatal stressors such as exposure to a terrorist attack are associated with increased incidence of schizophrenia in offspring
- Complications during pregnancy and birth can contribute to Schizophrenia
Substance abuse and schizophrenia
- Maternal substance abuse, and in particular, smoking is a risk factor
- Paternal and Maternal tobacco use has been associated with increased risk of schizophrenia
- Excessive alcohol intake increases the risk of schizophrenia
Mesolimbic dopamine pathway
• Evidence from pharmacological studies reveal
biochemical differences in the brains of people
diagnosed with Schizophrenia
• Positive symptoms perhaps the result of increased
activity of dopaminergic synapses in the mesolimbic
pathway
Mesolimbic dopamine pathway - chlorpromazine
• Chlorpromazine is an antipsychotic drug that
dramatically reduces the positive symptoms of
schizophrenia
• These drugs are antagonists for D2 and D3 dopamine receptors
Mesolimbic dopamine pathway - result of too much dopamine
• Mesolimbic pathway (VTA to the NAC) is a vital link in the process of reinforcement
• Agonist drugs for this pathway (Cocaine, L-DOPA)
strongly reinforce behaviour and produce the positive
symptoms of schizophrenia
• These effects are related. If reinforcement mechanisms are activated at an inappropriate time, then behaviours such as delusional thoughts might be reinforced – this could be associated with paranoia.
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