Attention deficit hyperactivity disorder (ADHD) is often considered to be a result of a poor upbringing and lack of motivation and a cause of low energy and laziness. However, it is not a condition that is induced by any one of the abovementioned factors. If you have ADHD, you are prone to come across these factors. ADHD can be caused by a number of factors that affect the functioning and development of the brain.

Let us look at some of the categories of causing factors.

Heredity
Heredity is one of the most prominent causes of ADHD. It is considered to be the most prominent factor on the basis of studies related to family, adoption, molecular genetic research, and research on twins.

Family studies
Family studies have shown that if a trait has a genetic basis, the chances of its occurrence among the biological family is significantly higher. Similar to other traits, ADHD also runs through families. It is observed that over 25% of the children suffering from ADHD have acquired it from their relatives.

Adoption studies
It is a fact that children will inherit more traits from their biological parents as compared to their adoptive parents. The conditions of hyperactivity in children suffering from ADHD were compared to the occurrence of ADHD in their biological and adoptive parents. The results clearly showed that the biological parents have had a history of ADHD.

Twin studies
If you wish to determine that a condition is caused by a genetic factor, then one such way includes studying a large group of identical and non-identical twins. For starters, you must know that identical twins have the same genetic information, whereas non-identical twins do not comprise the same genetic information as that of their identical counterparts. Concordance rate refers to the probability of both the twins being affected similarly by a condition. The concordance rate is important in this case as it is higher among identical twins and rare among non-identical twins. A major number of studies in this regard have hinted that ADHD is highly heritable. Even after these studies were carried around different parts of the world by different researchers, the consistency in their results is remarkable. The concordance rate of a study conducted in Australia showed the rate to be as high as 82% among identical twins and 38% among non-identical twins.

Molecular genetic research
Even if twin studies show that ADHD can be caused by genetics, they do not tell us which genes have been transferred to result in this condition. In this regard, genetic research in this field has increased in the past few years, and the primary focal point for now has been dopamine genes. Two dopamine genes—DAT1 and DRD4—have been said to be linked with ADHD by many scientists.

Exposure to toxic substances
Researchers have been widely looking at this cause of ADHD and have found that many mothers who have been smoking or consuming alcohol during pregnancy have induced behavioral and learning problems in their children. Similarly, if there is high lead exposure, it results in the induction of hyperactivity; especially, if the child is exposed to it in the first three years of their life. Nicotine, alcohol, and lead can have varied impacts on the developing brain tissue of a child. Such abuse can be sustained and potentially last throughout the life of the child. However, the exposure to such substances only limits to ADHD and does not become a cause for any major differences in brain development.

Injury to the brain from trauma, strokes, brain tumors, or disease
A heavy injury to the brain can result in trauma, external injury, brain tumor, stroke, or a disease. These conditions often cause inattention and poor regulation of the impulses, leading to hyperactivity or ADHD. However, the occurrence of ADHD due to an injury to the brain is not very typical and is only seen in rare cases.

Let us look at some misconceptions regarding ADHD

Hormones
There have been many studies that have proven heredity as a cause of ADHD, but there are none that have shown hormonal changes or insufficiency as a cause of ADHD. Hormone malfunctions or deficiency does not cause hyperactivity.

Diet
In the early 1970s, allergies to food substances and certain diet plans were considered to be causing factors of ADHD. However, this claim was overturned by research in the past few decades as there was no clear indicator to back it. Although there are a few claims that are still prevalent that consider body sugar to be a causing factor for ADHD, there is no research to back this claim either.