Is ADHD a Genetic Disease?
DHD or attention deficit hyperactivity disorder is a commonly occurring behavioral disorder. Diagnosed commonly in childhood, the exact cause of ADHD still remains unknown. The condition can also be diagnosed in adulthood, as adults can also experience the symptoms of the condition. It seems like with each passing year, the prevalence of ADHD is growing. In the United States alone, nearly five percent of children have ADHD. This number is expected to be around 2.5 percent for adults. Over the years, more and more evidence has been piling up that shows that ADHD might very well run in families. The genetic evidence for ADHD definitely cannot be ignored. Furthermore, studies conducted on twins and families clearly show that genetic factors are one of the main causes of ADHD. In fact, it is estimated that nearly 80 percent of the variation in the level of severity of ADHD is the direct result of genetic factors.
Causes of ADHD
In spite of years of research in this field, the exact of ADHD remains unknown. However, there are several factors that may ultimately cause the disease. These include:
- Genetics: ADHD is known to run in families.
- Chemical imbalance: It is suspected that brain chemicals in ADHD patients might be imbalanced.
- Changes in the brain: Regions in the brain that control attention is suspected to be less active in ADHD sufferers.
- Toxins, such as lead, that are known to affect brain development in children.
- Brain injury or brain disorder: Damage to the frontal lobe, or the front of the brain, may be responsible for causing problems in impulse control and emotions.
- Factors that affect brain development in children such as infections, smoking, and drinking during pregnancy, malnutrition, substance abuse during pregnancy, etc.
Out of all these factors, genetics is suspected be the main cause of ADHD as studies have shown that every three out of four children who suffer from ADHD have a relative with the condition.
ADHD and that One Relative
Several studies have proven that having even one family member, be it a close relative or a distant one, makes you more prone to having the ADHD disorder. Children who suffer from ADHD usually have either a sibling, parent or even a close relative with ADHD. In fact, research from the National Institutes of Health (NIH) has established that nearly one-third of fathers who suffer from ADHD or who had ADHD in the past, will have children who are more likely to be diagnosed with ADHD, thereby proving a direct genetic connection.
Scientists are of the opinion that ADHD is no doubt a complex condition that arises in the brain and directly involves at least two genes. While there are non-genetic causes of the disease as well, but the genetic connection seems to be the predominant cause of ADHD.
ADHD and the Case of Twins
Many studies have been conducted on identical twins to determine if there is a genetic connect for ADHD. As identical twins have the exact same genetic material, therefore, if a disorder is transmitted genetically, both the identical twins will be affected in the same manner as well as the probability of them both suffering from ADHD will be extremely high. This probability is lower in non-identical twins. Several major identical twin studies have provided strong evidence that ADHD is passed on genetically. In spite of being conducted by different researchers in different countries, the results of all the studies have shown that ADHD is highly heritable. Let us take the example of one such study conducted by Dr. Florence Levy and her colleagues. The team studied 1,938 families with twins and siblings in Australia. The study found that as compared to other behavioral disorders, ADHD has an exceptionally high probability of heritability. The study reported a concordance rate of 82 percent for ADHD in identical twins. On the other hand, the concordance rate in non-identical twins was a mere 38 percent.
Role of the Missing DNA
Unlike the many potential environmental causes of ADHD, the genetics or the DNA behind ADHD cannot be changed. Due to this fact, most of the ADHD research going on nowadays is focused on understanding the genes that cause ADHD. In 2010, researchers from the Cardiff University were able to successfully identify rare chromosomal deletions and duplications that are responsible for causing neurodevelopmental disorders similar to ADHD. The study showed that these small pieces of DNA were either missing or duplicated in the brains of children who were suffering from ADHD. The same genetic segments are also linked to disorders such as autism and schizophrenia.
The study also found that there were significant overlaps between these DNA segments, known as copy number variants (CNVs). The fact that these genetic variants are implicated in schizophrenia and autism also provides strong evidence that ADHD is a genetically passed on neurodevelopment disorder. In other words, one can say that the brains of children suffering from ADHD are different from those of other children.
Brain Tissues and ADHD
The brain has a big role to play in ADHD. Researchers from the National Institute of Mental Health (NAMI) have been able to identify the region of the brain that gets affected by ADHD. This evidence is of particular importance because NAMI scientists were able to establish that people suffering from ADHD have thinner tissues in the region of the brain associated with attention span. In children, however, it was found that the brain tissue develops into normal levels of tissue thickness as they become older, thus lessening the severity of ADHD symptoms.
Should Parents Having ADHD Worry About Passing It On to Their Children?
Being a parent if you suffer from ADHD, then it is, of course, a natural worry that you might be passing on the disorder to your child. While you cannot control whether or not your child will inherit the genes of ADHD, you do have a control on vigilantly observing your child’s potential symptoms. It is a good idea to keep your child’s pediatrician informed about the history of ADHD in your family. The easier the signs and symptoms of ADHD get identified in your child, the sooner your child’s doctor will be able to respond to them, thus beginning treatment at the earliest possible. This will also help your child learn to deal with the symptoms from an early age, thus allowing him or her to have a better quality of life.
While studies conducted on twins lend support to the theory that ADHD is passed on genetically, it does not identify the specific genes that are linked to this disorder. Importance of genetic research into ADHD has gained prominence over the last five years only and the research is focusing on identifying the specific genes that are involved in the passing on of ADHD. The starting point for these studies has been the neurotransmitter dopamine genes, particular two dopamine genes – DAT1 and DRD4. These two genes are thought to be associated with ADHD by many scientists around the world. While genetic studies have already shown promising results, more information needs to be gathered, particularly centering on what genes are responsible for causing ADHD.
Answers to such questions will also make it possible to find better and customized treatments for people suffering from ADHD.