Is bipolarity hereditary?

La bipolarity can be a good teacher. It's an everyday challenge but it can allow you to do almost anything else in your life.

From the start, the fact that there would be a part of genetic In the bipolarity comes back regularly.

Thus, having one or more parents bipolar, will increase the chances of being one yourself.

Hereditary bipolarity: So let's see together, today, the link that exists between herity/genetics and bipolarity.

Like the forms of bipolarity, the causes of the disorder are multiple and above all quite poorly, despite scientific advances.

Etiological studies - studies of the causes and factors of a disease - are still few and the disease varies so much from patient to patient that it is difficult to know and compare the triggers of bipolar disorders.

In addition, the bipolarity belongs to the group of psychiatric illnesses with complex inheritance. That is to say, it is characterized by the interaction of numerous genetic factors and factors related to the environment (early life events, loss of a parent, emotional deficiency, sexual assaults in childhood, death, etc.).

Although genetics account for 60% in the origin of disorders, they are ultimately only triggered by interaction with one or more environmental factors.

Studies conducted on the link between genetics and bipolarity

Although bipolar disorders can occur in any individual, there is still a strong genetic vulnerability in the patients concerned.

All scientific studies agree that some families are more affected by bipolarity than others and that this trend cannot only be explained by shared conditions such as education, culture or even family history.

So here is a summary of the studies carried out on the subject since the 70s and their discoveries.

1. Hereditary bipolarity: Studies of the concentration of pathology in the family

The first studies, which were essentially statistical, consisted of studying large samples of Type I bipolar (the most marked type).

For first-degree parents (children/parents, brothers/sisters), it has been shown that the risk of developing a bipolar disorder was 10 times greater than the rest of the population.

For reference, in the general population the risk of having unipolar disorder is 3% and 1% for bipolar disorder type 1 (Reich et al, 1982).

We therefore reach a risk of around 10% for the immediate family.

This study is a strong indicator of the hereditary nature of bipolarity.

However, a statistical study is not enough to differentiate a genetic origin from an environmental origin of the disease.

Indeed, many environmental factors are shared within a family and an additional impact on the onset of pathology.

2. Twin studies (Bertelsen et al. [1977] + McGuffin et al., 2003)

It was by studying twins that heredity was recognized as a determining factor in the triggering of bipolar disorders.

The consistent occurrence of bipolar disorder is 60% for identical twins called monozygotic (which are therefore almost genetically identical), compared to only 20% of cases for so-called dizygotic “false twins” (who share on average half of their genes).

These findings point to an at least partially genetic transmission of the disorder.

But, since between two identical twins the agreement is not 100% (if one is reached the other is not always reached), the hereditary factor does not explain everything.

In addition, environmental factors influence the phenotype (the way in which genes are expressed), which further complicates the analysis of genetic origin.

Therefore, there is no simple transmission mechanism.

There is indeed a hereditary component of the disease, but how can we distinguish between heredity and the environment?

3. Studies on adopted children (Mendlewicz and Rainer, 1977)

In 1977, a study was carried out to compare the rate of bipolarity between the natural and adoptive parents of bipolar and non-bipolar ones.

During this study, 12% of adoptive parents of bipolar children had an affective disorder ( bipolar, unipolar, schizoaffective disorder, cyclothymia).

This rate was the same for non-bipolar children.

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Conversely, 31% of natural parents of bipolar children had an affective disorder, compared to about 12% of natural parents of non-bipolar children

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These figures show us that the intervention of hereditary factors foreign to the educational environment plays an important role in the transmission of bipolar disorders.

Studies conducted on families affected by bipolarity have shown that first-degree parents of people diagnosed with bipolar are 10 times more likely to also have the disorder than the rest of the population.

Twin and adoption studies have confirmed that genes play an important role in the transmission of bipolarity, without fully explaining the transmission of the disorder.

So it does not exist no single transmission gene, but it is accepted that several vulnerability genes intervene, that's why we're talking about disease “with complex heritability.”

‍Possess the genes of vulnerability does not determine that one will develop the disease. The conditions induced by the presence of these genes of vulnerability only constitute a state of frailty, in which the subject is at greater risk of developing bipolar disease than the person who does not have these conditions.

Identifying vulnerability genes: a key challenge (hereditary bipolarity?)

While research has benefited from advances in genetics, it still faces obstacles such as the heterogeneity of the disease and the lack of understanding of the mode of genetic transmission.

And because of the great clinical diversity of bipolar disorders, this research requires very large patient samples, which complicates research.

The current scientific challenge is to identify vulnerability genes in order to improve the procedures of Diagnostics, the development of new treatments as well as the development of preventive strategies.

Currently, molecular biology studies have identified regions of the genome likely to contain these genes of vulnerability like the chromosomal regions 3p14, 4p16, 12q23-q24, 16p13, 20p12, and 21q22. Some genes in particular such as SYNPR and CADPS are studied. These and other paths are currently being explored.

And for our children?

What is behind this question of heredity, for me like so many other people suffering from bipolar disorders, it's the delicate and painful question: “Will I pass it on to my children?”

Perhaps in a few years, as research progresses rapidly, we will be able to detect if our children have the genes of vulnerability, and to prevent the occurrence of the disease.

But in the meantime, we can do more than be afraid.

What's still clear is that our genes don't determine everything.

And anyway, having these factors of vulnerability is not a condemnation. We don't have to be afraid to pass them on.

La genetic is complex, and genes can both bring very positive things as well as vulnerability to a disease.

Above all, understanding environmental factors can allow us to avoid the onset of the disease, whether we have transmitted the vulnerability genes or not.

This gives us the opportunity to act on our children's environment in order to prevent the onset of the disease.

So good news, which leaves us on a note of hope while waiting to know even more.