Schizophrenia can run in families.
A first degree relative shares 50% of genes. (Second degree shares 25%.)
Kendler et al showed first degree relatives are 18 times more at risk than the general population.
Family studies are often inconclusive because they are conducted retrospectively.
They compare those already diagnosed. A longitudinal study can provide more reliable data.
To separate genes from environment, researchers found M.Z twins raised apart, where one twin has schizophrenia.
Gottesman and Sheilds used the Maudsley twin register and found 58% concordance.
Offspring of a non-affected twin should also be at risk, Fischer found that…