Genetic explanation of unipolar depression

Genetic explanation of unipolar depression

There is evidence that if someone in your family has been diagnosed with unipolar depression then there is a higher risk that you will also be diagnosed with depression. This suggests that unipolar depression might be inherited through genes shared by family members. However, not everyone in a family will develop depression, so it is not clear exactly what role genes play in causing depression. A recent study by Craig Hyde et al. (2016) found that 17 different gene variations were linked to developing depression. This means that there are many different possible combinations of genes a person could inherit that would lead to depression, which makes identifying the people at risk from developing depression quite a challenge.

Twin studies

Twin studies are useful for looking at the influence of genes. Identical twins (monozygotic) share 100 per cent of the same genes, while non-identical/ fraternal twins (dizygotic) share only 50 per cent – the same as other siblings share.

A study by Peter McGuffin et al. (1996) found that if one monozygotic twin became depressed, there was a 46 per cent chance that their co-twin would also develop depression.

However, if a dizygotic twin became depressed, there was only a 20 per cent chance that the other twin would also develop depression. This shows that depression might be genetic because the monozygotic twins, who share more genes than the dizygotic twin pairs, were at greater risk of becoming depressed if one of them was diagnosed. Not all family members related to someone with depression will go on to become depressed themselves. One reason for this could be that there needs to be a trigger from the environment in order for the gene to become ‘active’. This would mean that some people might have a genetic predisposition to become depressed because they have a gene that increases their risk. However, they would only go on to become depressed if they are put into a stressful situation that triggers the gene’s effect on their mood. This combined explanation for depression is often called the diathesis-stress model.

Strengths and weaknesses of the genetic explanation

This explanation for depression has several strengths.

One strength is that if we can explain depression by looking at the genes people might inherit, we can take away the stigma of being diagnosed with depression. If becoming depressed is in your genes, people cannot blame you for being depressed. This means society might be more accepting of people with mental health disorders such as depression.

Another strength is that lots of research evidence supports the idea that some people are more prone to depression than others. For example Caspi et al. (2003) found that people with a variation of the serotonin transporter gene were more likely to react negatively to stressful life events and develop depression. This would support the claim that genes play a significant role in developing depression.

One weakness of the genetic theory of depression is it is very deterministic because it assumes that if you have certain genes you are likely to become depressed, and you have no way to change that. However, some people argue that this is not the case and instead believe you have a certain amount of free will to choose whether or not to ‘let yourself’ become depressed.

Another weakness is that some people argue that the genetic explanation of depression is reductionist because it fails to take into account other factors that can explain why someone may develop depression.

People often think depression is linked to life events such as a death in the family or someone losing their job. It is too simplistic to assume that it is just an abnormal gene that makes someone depressed.