Final answer:
The increased risk of bipolar disorder among relatives is approximately 10x, with both genetic and environmental factors contributing to its etiology. So the correct answer is option (C).
Step-by-step explanation:
The approximate increased risk of bipolar disorder among relatives of individuals with the disorder is about 10 times greater. The current understanding of its etiology is that both genetic and environmental factors contribute to the development of this condition. Studies suggest that genetics play a significant role; however, environmental factors can also influence the likelihood of developing bipolar disorder, just like they can affect the risk of other disorders, such as schizophrenia and eating disorders.
For example, a child with a high genetic risk for schizophrenia is more likely to develop the condition if they are raised in a disturbed family environment compared to a healthy one. Similarly, inherited risk factors may significantly increase the risk of particular diseases, like certain cancers, but environmental influences must also be present for the disease to manifest.