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Why mental illness runs in families

13 Apr 2016

Your parents and mental health

If someone in your family has a mental illness you might be worried that you are at risk of developing one too. It does seem that mental illness can be passed on in families through genes. However, we do not fully understand how this works. Mental illness may be passed on in family members for reasons other than just genes.

The nature vs. nurture debate revolves around the following question: what factors impact the mental development of an individual: nature (that is, the genetic makeup of a person) or nurture (that is, how a person is raised, and in what environment)?

Just as human beings inherit certain physical traits from their biological parents (such as height, eye colour, and even predisposition to physical ailments), human beings can also inherit a propensity for certain mental disorders.

Many studies in the nature versus nurture conflict centre on identical twins. Researchers look not only at twins raised together but those raised apart to determine whether or not a certain trait is biologically programmed or if it evolves as a result of the environment in which one twin was raised.

Most researchers now agree to some extent that both biology and environment play important roles in shaping people. Just as children may share traits with biological parents, adopted children may also share many traits and habits with their adoptive parents.

How nature affects mental health

While nature, or genetics, has been proven to be an important factor in the development of some mental health conditions, such as schizophrenia, bipolar, and major depression, the development of mental illness is not entirely genetic. Nature, or genetics, has been proven to be an important factor in the development of some mental health conditions, such as schizophrenia, bipolar, and major depression: Bipolar, for example, is four to six times more likely to develop when there is a family history of the condition.

However, although the importance of genetic factors cannot be denied, the development of mental illness is not entirely genetic. Take identical twins, for example: They share genes, yet if one twin develops schizophrenia, the other twin only has a 50% chance of also developing the condition. This shows that nature, while it plays an important part, is not the only contributing factor.

How nurture affects mental health

Certain genetic factors may create a predisposition for a particular illness, but the probability that a person develops that illness depends in part on environment. When a genetic variant indicates the possibility of development of a mental illness, this information can be used to direct positive (nurturing) behaviour in such a way that the condition may not develop or may develop with less severity.

Researchers at the University of Liverpool recently found that while a family history of mental health conditions was the second strongest predictor of mental illness, the strongest predictor was in fact life events and experiences, such as childhood bullying, abuse, or other trauma, supporting the idea of nurture’s significant role in the development of mental health issues.

Nature x nurture

Many scientists reject the debate by emphasizing “nature x nurture.” In this formula we say nature and nurture are inseparable. Some genes, for example, cannot be activated without certain environmental inputs. The development of vision is a prime example of this. People cannot develop normal sight without exposure to visual stimuli. Similarly, some environmental inputs may be undermined by some genes. For example, some lifelong smokers may never experience smoking-related illnesses, and this may be due at least in part to their genes.

References

GoodTherapy.org: Nature vs. Nurture Debate

Other sources:

  1. Agin, D. P. (2010). More than genes: What science can tell us about toxic chemicals, development, and the risk to our children. Oxford: Oxford University Press.
  2. DualDagnosis.org: Alcoholism Nature vs. Nurture 
  3. ADAMHS: Facts about Bipolar Disorder
  4. Everyday Health: Mental Illness May Be In Your Genes
  5. Live Science: Twins Separated at Birth Reveal Staggering Influence of Genetics 
  6. Moore, D. S. (2003). The dependent gene: The fallacy of nature vs. nurture. New York, NY: Henry Holt.
  7. Decoded Science: Nurture Over Nature: Mental Illness and Traumatic Life Events

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