Identical twins have so much in common: the same genes, the same birthday, the same physical features, and very often jokes that only the two of them seem to understand.
Unfortunately, they also share other things that are not so innocuous. Thus, if one identical twin develops schizophrenia, the chances are up to 65% that the other twin will also develop it. They also share high risks for bipolar disorder, learning disabilities like dyslexia, autism and other mental disorders. This high level of shared risk is evidence for a strong genetic component in mental illness.
But the risk that both identical twins will develop the same mental disorder is never 100|%. Which clearly signifies that genes are not the only culprit in mental illness. Other factors are also involved. These factors are the environmental signals that we are all exposed to; there are hundreds of them, including childhood trauma, diet, lifestyle habits like smoking, medications, chronic financial problems, military combat and social isolation.
Any person’s risk profile for mental illness thus becomes a matter of a dynamic and complex interplay between nature (genes) and nurture (environment). 'Epigenetics' is an emerging frontier of science that focuses on how some of our genes get switched on or 'expressed' by aspects of the environment – and how mental illness can be one of the outcomes of such gene expression.
Here’s an overview of the major nature and nurture operants that may come into play at different stages of our lives to trigger one or more mental disorders:
Genes take centre-stage: Mental illness is more common in people whose biological (i.e., blood) relatives, such as a parent or sibling, also have a mental illness.
The children of two parents with mental illness represent an extremely high-risk group. For instance, if one parent has schizophrenia and the other has bipolar, their children are more likely to develop one of these disorders, or another mental illness, than children with only one parent with a mental disorder.
Ongoing research has identified some of the genes associated with an increased risk for certain mental illnesses, including schizophrenia, bipolar disorder, depression, autism, Alzheimer’s disease and ADHD (attention deficit hyperactivity disorder). But the genetics of mental disorders is not at all simple. There are likely hundreds of genes involved in a specific mental illness, researchers say, and each of these genes in itself may confer only a small risk. Sometimes random, rare mutations involving very many genes may be involved. Although the role of environmental factors has been recognized, the evidence is strong that in some mental illnesses, like schizophrenia and autism, genes may play a more dominant role than the environment.
Pre-natal insults: The 'environment' begins to shape a person’s risk profile for mental illness even before birth. By the time a baby is born, it has already been influenced by a myriad events occurring in the womb. If some of these factors have negatively impacted the fetal brain, the resulting damage has a more global effect than damage that occurs after birth.
Such negative influences include maternal malnutrition (in particular, severe protein deficiency) which has been linked to an increased risk for ADHD in the child; maternal obesity, linked to a higher risk for anxiety disorders and learning impairments; smoking/alcohol abuse by the pregnant mother, linked to an increased risk of ADHD and learning impairments.
Maternal infection during pregnancy (e.g., flu) can up the risk for bipolar disorder, autism, schizophrenia and ADHD in the child. Scientists hypothesize that it is not the infection itself but the mother’s immune response to it (and the resulting storm of inflammatory substances produced) that can wreak damage to the developing fetal brain.
The problems generated by pre-natal damage to the brain may not show up until puberty when the brain undergoes major changes that could trigger psychiatric symptoms.
Different brain chemistry: Brain cells communicate with one another either through chemical messengers (called 'neuro-transmitters') or through electrical signals. The risk for several mental illnesses, such as clinical depression, schizophrenia and ADHD, is elevated in those persons in whom the process of transmitting messages through chemicals does not work correctly. For example:
– Problems in making or using glutamate, the most common neuro-transmitter, have been linked to many mental disorders, including autism, depression, obsessive-compulsive disorder (OCD) and schizophrenia.
– Some studies suggest that having too little dopamine, or problems using this chemical in the thinking and feeling regions of the brain, may play a role in disorders like schizophrenia and ADHD.
– Research shows that people with depression often have lower than normal levels of serotonin.
Gender: Just being a woman puts you at greater risk for being diagnosed with depression or anxiety. Women are 70% more likely than men to experience depression during their lifetime, according to studies examining gender differences in rates of mental illnesses.
On the other hand, men are at greater risk than women for substance abuse disorders and anti-social disorders, these studies show.
The gender differences may be related to how the sexes deal with their emotions. Women are more likely to internalize their emotions and withdraw, leading to depression and anxiety. Men, however, are more likely to externalize their emotions and act out.
That apart, women’s higher depression rate may be linked to biological, hormonal, life cycle and psycho-social factors. Hormones directly affect the brain chemistry that controls emotions and mood. For example, women are vulnerable to developing post-partum depression after giving birth, when hormonal and physical changes and the responsibility of caring for a newborn can be overwhelming.
Similarly, the culturally-defined role of women in many societies exposes them to greater stresses, which, together with other factors including family violence and abuse, lead to higher rates of depression and anxiety. A study in the rural and urban areas of Northern Goa found that alcohol abuse and chronic drunkenness by the male partner were linked to increased risks for depression and anxiety disorders among married women; this finding is in line with study results from other countries.
But the Goa study was unique in measuring how women’s attitudes regarding the acceptability of men’s use of violence against their partners is linked to an increased risk of depression and anxiety disorders in these women. Women’s belief that certain reasons (such as 'being sexually unfaithful' or 'being disrespectful') make it acceptable for a man to use force with his spouse are, of course, a reflection of gender inequities and lead to these women viewing themselves as less valuable and therefore having fewer choices than men – including fewer options to cope with the distress resulting from men’s violence. “This could lead to ‘learned helplessness’,” the researchers write, “setting the stage for clinical depression and anxiety.”
Age: Adolescence constitutes a critical formative stage in life, marking as it does the passage from childhood to adulthood. The challenges of this transition often act as the trigger that causes mental illness genes, lying dormant, to get expressed.
Before puberty, boys and girls are equally likely to develop depression. By age 15, however, girls are twice as likely as boys to have had a major depressive episode.
In addition, there are a number of other significant risks that have particular pertinence to this life stage. Tobacco/alcohol/drug use is one such risk, the onset of which typically occurs during adolescence. Adolescents exposed to family unrest or exhibiting behavioural problems in childhood are more likely to engage in substance abuse. And substance abuse is particularly hazardous for adolescents because the brain (and the rest of the body) are still developing at this age. Research shows that substance abuse and mood disorders like depression and bipolar disorder commonly occur together.
Older age is the single most important risk factor for cognitive decline and dementia. In addition, social and family isolation – and also bereavement – are significant predictors of depression in older age. Since chronic physical illness is also a risk factor for depression, its higher prevalence among the elderly further contributes to elevated rates of depression among them.
Life stressors: Stress has been found to be a significant contributor to the development of most mental illnesses. Difficult life circumstances during childhood, like the early loss of a parent, poverty, bullying, witnessing parental violence; being the victim of emotional, sexual or physical abuse or of physical or emotional neglect; and insecure attachment have all been associated with the development of depression and schizophrenia in adulthood.
Unemployment almost quadruples the likelihood of alcohol/drug abuse, and triples the odds of developing a phobia or a psychotic illness like schizophrenia. It more than doubles the risk of depression or an anxiety disorder, including obsessive-compulsive disorder.
Researchers know how stress works its harmful effects in the case of some mental illnesses. Inflammation is a key part of the stress response. Specialized proteins called cytokines are produced. In excess, cytokines lead to a cascade of events in the body that hinders production of the brain chemical, serotonin, which is a necessary ingredient for healthy mood. Depression is linked to low production of serotonin.
Serious/chronic ailments: Having a serious (non-mental) illness ups your risk of depression. These 'co-occurring' medical conditions include heart disease, stroke, cancer, HIV, diabetes, hormonal disorders and Parkinson’s disease.
While some disease processes directly affect the brain (examples include cerebral malaria, HIV, stroke and substance abuse), others primarily create a psychological burden due to the challenges of living with the condition (such as an altered lifestyle, or coming to terms with the prospect of prolonged illness or premature death).
Medications: Some medications used for long periods, such as the corticosteroid, prednisone, certain blood pressure medicines, sleeping pills and antibiotics, can cause depression or make an existing depression worse. Some anti-seizure medications are associated with a higher risk of suicide.
Co-occurring mental disorders: Having one mental disorder often puts you at risk for another. Thus, depression is often accompanied by an anxiety disorder such as GAD (generalized anxiety disorder), obsessive-compulsive disorder, social phobia, panic disorder or post-traumatic stress disorder (PTSD).
Children with autism are also at higher risk for some mental disorders such as anxiety disorders, ADHD or depression.
In one recent international study, across all countries studied, 75 per cent of those who had bipolar symptoms showed symptoms of at least one other disorder; most commonly, this was an anxiety disorder, especially panic disorder, followed by behaviour disorders (such as Conduct Disorder) and substance abuse disorders.
(The author, a former editor of 'Health & Nutrition' magazine, now works as a counselling therapist)