The causes of most mental disorders are unknown, but the dimensions are becoming more understood.

What we do know about causes:

• Several factors interact to produce a mental disorder:
  • Individual intrapsychic situation
  • family circumstances
  • social influences
  • biological and genetic factors
• Trauma and stress can be significant aggravating factors
• What initiates a disorder is usually different from what perpetuates it. What initiates and perpetuates a disorder may differ from what exacerbates it.
• A person may have a predisposition, or latent susceptibility, to a disorder which may be activated under certain conditions such as stress.

And, it is important to note:

• Not all aberrant behavior is a mental disorder. Interactions between various drugs that a person may be taking can cause problem behavior. These interactions can vary by age, sex, with various combinations of prescribed and over-the-counter medications.

Genetic factors in Mental Disorders

Based on studies of twins and adoptees:

• Disorders with a significant genetic link: Schizophrenia, Bi-polar disorder, Depression
• Disorders with a weaker genetic link: Panic attack, Obsessive-compulsive disorder

Source:

Essential Psychopathology and Its Treatment, Second Edition by Jerrold S. Maxmen and Nicholas G. Ward, pp 57-79.