Genetic basis:

• Family studies

  Family studies have confirmed that risk of schizophrenia increases in line with genetic similarity to a relative with the disorder

  • This relationship is shown by the findings from Gottesman's large-scale family study
  • IE someone with an aunt with schizophrenia has a 2% chance of developing it, increasing to 9% if the individual is a sibling and 48% if they are an identical twin.

  Family members tend to share aspects of their environment and many of their genes, so the correlation represents both
• Candidate genes

  Early research in this area looked for a single genetic variation in the belief that one faulty gene could explain schizophrenia

  • It appears that a number of different genes are involved, i.e. is polygenic
  • The most likely genes would be those coding for neurotransmitters including dopamine
• Candidate genes:

  Ripke et al combined all previous data from genome-wide studies of schizophrenia.

  Genetic make-up of 37,000 people with a diagnosis of schizophrenia was compared to that of 113,000 controls, 108 separate genetic variations were associated with slightly increased risk of schizophrenia.

  Because different studies have identified different candidate genes it also appears that schizophrenia is aetiologically heterogeneous, i.e. different combinations of factors, including genetic variation, can lead to the condition.
• The role of mutation

  Schizophrenia can also have a genetic origin in the absence of a family history of the disorder.

  One explanation for this is mutation in parental DNA which can be caused by radiation

  Evidence for mutation comes from positive correlations between paternal age (associated with increased risk of sperm mutation) and risk of schizophrenia, increasing from around 0.7% with fathers under 25 to over 2% in fathers over 50 (Brown et al. 2002).