Final answer:
Manic-depressive disorder, also known as bipolar disorder, has a strong genetic component, and MZ twins have a higher risk for diagnosis of mania if their twin has been diagnosed with bipolar disorder.
Step-by-step explanation:
Manic-depressive disorder, also known as bipolar disorder, has been found to have a strong genetic component. Monozygotic (MZ) twins, who share 100% of their genetic material, have a higher risk for diagnosis of mania if their twin has been diagnosed with bipolar disorder. Various studies have shown that the risk of developing bipolar disorder in MZ twins ranges from 32% to 68%, depending on the study population and other factors.
For example, a study by Merikangas et al. (2011) found that the prevalence of bipolar spectrum disorder in MZ twins was approximately 10 times higher compared to non-twin individuals. This indicates a significant genetic influence on the risk for the diagnosis of mania in MZ twins.
It's important to note that while genetics plays a significant role in the development of bipolar disorder, environmental factors can also contribute to the risk. The interaction between genetics and the environment is still being studied to better understand the complex nature of bipolar disorder.