Schizophrenia

• Schizophrenia

  • Serious mental disorder affecting 1% of population. More common in males, city-dwellers and lower socio-economic groups
• Diagnosis


  Identify symptoms and use classification system to identify the disorder (e.g. depression, OCD, schizophrenia etc)
• Classification


  Identify symptoms that go together = a disorder
• Diagnosis and classification are interlinked
• Main classification systems

  • DSM-5
  • ICD-10
• DSM-5


  One positive symptom must be present (delusions, hallucinations or speech disorganisation)
• ICD-10


  Two or more negative symptoms are sufficient for diagnosis (e.g. avolition and speech poverty)
• Hallucinations


  • Unusual sensory experiences that have no basis in reality or distorted perceptions of real things. Experienced in relation to any sense. For example, hearing voices or seeing people who aren't there
• Delusions


  • Beliefs that have no basis in reality - make a person with schizophrenia behave in ways that make sense to them but are bizarre to others. For example, beliefs about being a very important person or the victim of a conspiracy
• Negative symptoms

  • Loss of usual abilities and experiences
• Speech poverty


  • A reduction in the amount and quality of speech. May include a delay in verbal responses during conversation
• Avolition


  • Severe loss of motivation to carry out everyday tasks (e.g. work, hobbies, personal care). Results in lowered activity levels and unwillingness to carry out goal-directed behaviours
• One standardised test is a reliable and consistent way for clinicians to differentiate between schizophrenia and other disorders
• Reliability of diagnosis of schizophrenia

  • Good. Consistent diagnosis between clinicians and over time. DSM-5 criteria for schizophrenia is consistently applied, with test-retest reliability of 0.92, and inter-rater reliability of 0.97
• Validity of diagnosis of schizophrenia

  • Low. Criterion Validity- Whether different procedures used to assess the same individuals arrive at the same diagnosis. Cherie et al (2015) found that 68 clients were diagnosed with schizophrenia using ICD, while only 39 were diagnosed using DSM
• This suggests that schizophrenia is either over- or under-diagnosed, indicating low criterion validity
• However, the Osório study found excellent agreement between clinicians using different procedures derived from the DSM system. This means that the criterion validity for schizophrenia is good provided it is taken place within a single diagnostic system
• Comorbidity with other conditions

  • Limitation of diagnosis of schizophrenia. Depression (50% of cases), substance abuse (47%), or OCD (23%)
• Gender bias in diagnosis of schizophrenia

  • Limitation. Men are diagnosed with schizophrenia more often than women, in a ratio of 1.43. Men are more genetically vulnerable, or women have better social support, masking symptoms
• Cultural bias in diagnosis of schizophrenia

  • Limitation
• Cultural acceptance of symptoms

  • Hearing voices from ancestors is accepted in some Afro-Caribbean societies. Afro-Caribbean British men are up to ten times more likely to receive a diagnosis of schizophrenia as white British men, probably due to over-interpretation of symptoms by UK psychiatrists.
• Symptom overlap between schizophrenia and other conditions


  • Limitation- There is overlap between the symptoms of schizophrenia and other conditions, such as delusions and avolition in both schizophrenia and bipolar disorder. Schizophrenia and bipolar disorder may be the same condition, and schizophrenia is hard to distinguish from bipolar disorder
• This suggests that schizophrenia may not exist as a distinct condition
• Genetic basis of schizophrenia


  • Family studies
  • Candidate genes
  • Mutation
• Degree of genetic similarity


  Shared risk of schizophrenia
• Gottesman's large-scale study found someone with an aunt with schizophrenia has a 2% chance of developing it, for a sibling 13%, and for an identical twin 48%
• Early research looked unsuccessfully for a single genetic variation to explain schizophrenia
• Schizophrenia is polygenic-requires several genes
• Schizophrenia is aetiologically heterogeneous, i.e. risk is affected by different combinations of genes
• Ripke et al. (2014) combined all previous data from genome-wide studies and found 108 separate genes associated with slightly increased risk of schizophrenia
• Schizophrenia can also have a genetic origin in the absence of a family history because of mutation in parental DNA
• Evidence comes from the correlation between paternal age (associated with increased risk of sperm mutation) and risk of schizophrenia (Brown et al. 2002)
• Role of dopamine


  Dopamine (DA) is widely believed to be involved in schizophrenia because it is featured in the functioning of brain systems related to the symptoms of schizophrenia
• Original DA hypothesis


  • Hyperdopaminergia linked to subcortex
  • High dopamine activity in subcortex (central areas of the brain associated with hallucinations and poverty of speech (e.g. excess of DA receptors in pathways linking from subcortex to Broca's area)
• Updated version


  Hypodopaminergia linked to prefrontal cortex
• Updated hypothesis has added low levels of DA in the prefrontal cortex (responsible for thinking) could explain negative symptoms
• Genetic variations (see above) and early experiences of stress make some people more sensitive to cortical hypodopaminergia hence subcortical hyperdopaminergia (Howes et al.)
• Ose strength


  • Strong evidence base
• Adoption studies


  • Gottesman facing page
  • Tienari et al. 2004
• Genetic similarity


  Increases risk of schizophrenia