Genetic explanation of Schizophrenia

It has been known that schizophrenia runs in families. This could be because family members share the same disadvantaged environment, but a large body of research evidence suggests that genetic factors are also important.

Family studies:

First-degree relatives (parents, siblings, offspring) share an average of 50% of their genes whilst second-degree relatives share around 25%. Kendler et al 1985 showed that first-degree relatives of those with schizophrenia are 18 times more at risk than the general population.

Evaluation:

Family studies are often inconclusive as they are conducted retrospectively, that is, they are comparing a cross section of people who have already been diagnosed. A longitudinal study can provide more reliable data as it follows the same group of people over a period of time and make comparisons before and after any of the signs of illness occur.

Twin studies:

Many studies have been conducted and have shown that monozygotic (identical) twins, who share 100% of their genes, have much higher concordance rates (the likelihood of both twins being affected) than dizygotic (non-identical) twins, who share only 50%. Researchers seek out MZ twins that have been reared apart where at least one has been diagnosed with schizophrenia. Gottesman & Shields 1982 used the Maudsley twin register and found 58% were concordant for schizophrenia. A study by Fischer 1971 found that 9.4% of offspring from a non-affected discordant MZ twin developed schizophrenia- much higher than the general population (1%). A study in London by Cardno found a 40%…