Genetic Determinants of Mental Illness

Have you ever wondered what causes someone to develop a mental illness?

It seems logical to assume that some mental health problems might arise from environmental interactions. For instance in the case of Post-traumatic Stress Disorder, the set of symptoms characteristic of this mental illness occur as a result of a traumatic event the person has experienced such as sexual assault, warfare or even traffic collisions. Other influences such as social isolation, exclusion, bereavement, disability and relationship breakdowns are also known to be risk factors for the development of certain mental illnesses. Yet we know that not everyone who has been through such experiences will necessarily go on to develop a mental illness, and not everyone with a mental illness may have had such experiences. This leads us to an interesting question. Do genetics play a role in the development of psychiatric disorders?

Scientists have long recognised the tendency of some mental illness to run in families. Indeed, a family history of mental illness is a risk factor for developing a psychiatric disorder. Example of such disorders with a strong familial component include bipolar disorder, major depression, schizophrenia, autism and attention deficit hyperactivity disorder (ADHD). Further pointers to the potential genetic roots of these disorders lie in their shared symptoms, suggesting they may also share similarities at a biological level.

An international research consortium conducted an analysis to further investigate the basis of these claims. Data from genome-wide association studies of these disorders were used and their genetic markers scanned in search of tiny variations appearing more often in people with these psychiatric disorders than those without. In total, 33,000 patients who had been diagnosed with at least one of the five aforementioned disorders were screened for evidence of illness-associated genetic variations. Their results were compared to a group of 28,000 people with no major mental illnesses. Interestingly, the study discovered variations that were significantly associated with all five disorders. Of note, variations in two genes encoding cellular machinery regulating the flow of calcium in neurons was found. A variation in one of these genes called CACNA1C had been previously associated with bipolar disorder, schizophrenia and major depression. CACNA1C has also been known to influence brain circuitry involved in functions that are often disturbed in psychiatric illnesses such as emotion, thinking, memory and attention. Furthermore, researchers also discovered illness-linked variation for all of these disorders in particular regions spanning multiple genes located on chromosomes 3 and 10.

Although the results of the study were statistically significant and certainly of great interest, the genetic association alone cannot be said to account for the development of these disorders. In fact, these genetic association may contribute only a small amount to the risk for mental illness. As such, findings such as these should not be looked upon as the answer to our question on why some people develop mental illnesses and others do not. Rather, it should be taken with a grain of salt and appreciated for its potential to enable more accurate diagnosis of psychiatric illness and as a window through which we may slowly begin to better understand the factors contributing to the development of mental illness.

References

Cross-Disorder Group of the Psychiatric Genomics Consortium. Identification of risk loci with shared effects on five major psychiatric disorders: a genome-wide analysis. Lancet. [Internet]. 2013 [cited 2016 Jan 29];381(9875):1371-9. Available from: PubMed