genetics

• candidate genes


  may be due to polygenic genes- number of genes appear to increase risk of schizophrenia,

  different combos of factors could lead to schizophrenia so it is said to be aetiologically heterogeneous
• twin studies


  directly look at comparisons between siblings who were born at the same time and who have thus had early identical upbringings. Therefore we can study the relative contribution of genetic and environmental influences. If monozygotic twins (M.Z. identical) twins are more concordant than dizygotic (D.Z. non-identical), then this suggests greater similarity is due to genetic factors.
• family studies


  -schizophrenia is more common among biological relatives of a person with schizophrenia and that the closer the degree of genetic relatedness, the greater the risk (as twin studies have). For example, Gottesman found that children with two schizophrenic parents had a concordance rate of 46%, children with one schizophrenic parent a rate of 13%, and siblings (where a brother or sister had schizophrenia) a concordance rate of 9%.
• adoption studies


  Because of the difficulties of disentangling genetic and environmental influences for individuals who share genes and environment, studies of genetically related individuals who have been reared (brought up) apart are used.
• gene mapping


  Genes associated with increased risk included those coding for the functioning of the neurotransmitter dopamine.  It has been found that the NRG3 gene variants interact with both NRG1 and ERBB4 gene variants.
• limitation of twin studies

  Gottesman & Shields reviewed five twin studies and reported concordance rate of 74% for monozygotic and 24% for dizygotic twins, shows sharing the same genes affects schizophrenia diagnosis.

  HOWEVER, not 100% for mz so environment must also play a role, mz might have more of a similar environment than dz which could have result in both dz twins developing schizophrenia
• strength twin studies plus contrast

  Kety & Ingraham (1992) found that the prevalence rates of schizophrenia were ten times higher among genetic rather than adoptive relatives of schizophrenics.

  however he used a small sample