Genetic inheritance

Research into genes causing schizophrenia

• Ripke et al reported 108 genetic variations that could mediate a vulnerability to the disorder, including variations on chromosomes 8 and 11, and the C4 gene

• Hong et al found a variation on the gene TPH was far more common in Chinese patients with schizophrenia (this codes for serotonin production)

Genetic inheritance

• Some people may have a predisposition to schizophrenia, and hence the condition is at least partly inherited, meaning it runs in families through faulty genes

• Having certain genes increases a person’s vulnerability to developing schizophrenia, inheriting biochemical imbalances or brain structure abnormalities

C4 gene function

• C4 is found at synapses in the CNS and mediates the pruning of synapses that normally takes place in development

• A faulty variant of C4 is a risk factor for schizophrenia as this can lead to hyper-pruning

• Research supports the idea that excessive hyper-pruning can lead to symptoms of schizophrenia

• This may help to understand the mystery of why brains from people with schizophrenia tend to have a thinner cerebral cortex with fewer synapses than unaffected individuals

Gottesman & Shields findings

• Children of 2 schizophrenic patients who share 100% genetic similarity, have a 46% chance of developing the disorder

• MZ twins who share 100% genetic similarity have a 48% chance of developing the disorder if one twin is diagnosed

• First degree relatives share 50% genetic similarity have a 13% chance of developing the disorder if a parent is diagnosed

• In second degree relatives, like grandchildren, share 25% genetic similarity and have a 5% chance of developing schizophrenia, if a grandparent is diagnosed.

MacDonald & Schultz (2009) - Twin study

• Suggested among MZ twins, if one twin is diagnosed with schizophrenia then the other is 99x more likely to suffer from the condition

• This implies that genetics are involved in the development of schizophrenia

Tienari et al (2000) - adoption study

• 164 adoptees whose biological mothers were diagnosed with schizophrenia, matched with children whose biological mothers did not suffer from schizophrenia

• Found 7% of the sample whose biological mothers had schizophrenia had also been diagnosed with the condition compared to just 4 from the control group

• Validates the idea that schiz has a genetic component as adoptees do not share environmental influences with their biological mothers and provides concurrent validity for the role of genes in schiz

Research Support (+)

• Joseph et al - 40% concordance rate for MZ twins and a 7% concordance rate for DZ twins. The higher concordance rate for schizophrenia for MZ twins suggests genes have some influence of the development of schizophrenia

• Implies schizophrenia may be caused by genetic inheritance, possibly through a faulty C4 gene

Incomplete explanation (-)

• Faulty genetics cannot be the sole cause of schiz, as if this was the case MZ twins would have a concordance rate of 100% as they share the same genotype. 

• Nurturing influences must therefore play a role in developing schizophrenia, e.g. stress, drugs, alcohol and a difficult childhood (i.e. deprivation and/or abuse)

Biological determinism (-)

• Although psychology is seeking in general laws to explain all behaviours, this genetic theory into schizophrenia overlooks many aspects

• This implies that the account neglects to consider the role of environmental factors as well as free will in the development and recovery from schizophrenia

Applications (+)

• Vulnerable groups in society who have relatives suffering from schizophrenia are often advised by clinicians on their risk of developing the disorder

• Individuals with schizophrenia would be made aware of the risk of their biological children developing the disorder, so they can think about alternative options like adoption or using surrogates.