Answer :
According to twin studies, genetic factors (genes) inherited from parents, as well as some environmental influence, cause familial influence on major depressive disorders. So it caused by the combination of both.
What is depressive disorder?
Depressive disorders are associated with mental conditions, and they can be influenced by both genetic and epigenetic factors. The children will have this disorder when their parents have it and it is passed on to them, but in epigenetic conditions, environmental factors influence this disorder. Because of stress, unavoidable judgments about one's appearance, and so on, the person is more likely to be affected by this. All these factors make someone feel depressed when they can't cope with the situation.
Hence, the familial influence on major depressive disorders is caused by genetic factors and by environmental factors too.
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