Genetics in ADHD Development

Introduction

Attention Deficit Hyperactive Disorder (ADHD) is a nature of childhood development disorder which is characterised by inappropriate development, severe, impairing attention, impulsiveness and overactivity. It is identified that ADHD can be present in adult and adolescence life. In this assignment, the genetic and environmental factors which are responsible to cause ADHD is to be discussed.

Genetic factors related to ADHD

The genes are found to have effective contribution to the development of ADHD among children. This is evident as in the study of Starck et al. (2016), the results inform that occurrence of ADHD among children who have mothers with ADHD is 41.3% whereas the children who have fathers with ADHD is 51%. This indicates that nearly half of the parents who suffered from ADHD are prone to have children with ADHD ensuring genetic transmission through inheritance as a potential risk to be considered for ADHD development. Thus, the genetic impact which causes ADHD can occur in various ways one of which is through inheritance as reported in the study. This transmission of the genes for ADHD among children mainly occurs at birth from their parents (Kim et al. 2017). In the study of Hong et al. (2018), an increased association between the control group and the children with ADHD in the 10R/10R genotype of the DAT1 variable number tandem repeats (VNTRs) is seen. Moreover, analysing the VNTRs of DRD4 gene revealed that 2R allele of the genes is associated with the development of symptoms of ADHD among individuals. Further studies made based on genome-wide scans have revealed that nearly 25-45 genes are related to the development of ADHD symptoms among the children (Mavrides, 2016). This indicates that ADHD is polygenic in nature which means more than one genes are responsible for causing the disorder with each of the genes showing small contribution to increase the risk of development of the disorder.

In the development of ADHD, the genes vary among individuals which lead to the disorder. Among them, the DAD4 or the DAT1 genes are found to be commonly present in all individuals and these genes are found to be present in multiple copies in form of tandem repeats along the chromosome. It is found that people with ADHD usually have more number of copies of the genes compared to normal individuals (Nuzziello et al. 2019). The increased number of copies of genes impact to alter the protein length which in turn changes the way the brain functions. The genes that are identified to be related to cause ADHD are found mainly expressed in the brain and not only in the expression of neurochemicals in the brain like norepinephrine and dopamine (Puentes-Rozo et al. 2019). The other way in which genetic factors leads to the development of ADHD is the development of de novo mutations in the genetic framework of the child which are not initially present in the genome shared from the parents. The new mutations mainly occur in the gametes due to external agents such as environmental toxins, X-ray machines and others (Mavrides, 2016). The DNA variation that is duplication or deletion of genetic information is found to be more common among ADHD children. This is evident from the study of Williams et al. (2010) where they reported that significant variations in DNA are nearly found in 14% of the children who are with ADHD compared to 7% of the children without having the presence of ADGD. Thus, it informs that DNA variations may also lead to the development of the disorder.

The gene-by-gene interaction is able to create risk of development of ADHD in children. This means that in case one risk gene for ADHD is already present then it indicates that a small increase regarding the development of disorder is present among individuals (Pagerols et al. 2018). The gene-by-environment interaction is another way in which genetic factors affects the development of ADHD. This means when a child inherits any genes that cause ADHD, the expression of the gene on interacting with certain agents in the environment magnify the risk for the disorder. For instance, children who have risk genes for ADHD on exposure to environmental factors such as radiation, chronic infections and others would be 8 times more at risk of development of the disorder compared to children who lack risk genes for the disorder (Mavrides, 2016). The epigenetic impact may also contribute to the development of ADHD in children. The epigenetic impact is the non-genetic influence on the existing genes which means that small methylated tags are inserted or attached on the gene after or during its transmission to the offspring. The tags influence the activation of the genes, in turn, influencing the function within the body and eventually affect the development of symptoms regarding the disorder (Adriani et al. 2018).

Environmental factors related to ADHD

There are various environmental factors which lead to raise the risk of development of ADHD in children out of which maternal smoking during pregnancy is one of the key factors. This is evident from the study of Sourander et al. (2019) where it is mentioned that higher level of cotinine level in mother during their pregnancy creates greater risk for the child to develop ADHD later. The cotinine is the biomarker for nicotine and increased cotinine levels are present when the individuals are exposed to higher level of nicotine through smoking of tobacco. In another study Joelsson et al. (2016), the fact is also supported that maternal smoking during pregnancy leads to risk of ADHD development. This is evident from the results where it is mentioned that out of the participants 2.2% of pregnant women smoked in their first trimester whereas 28.1% smoke after the first trimesters and in the control groups the figures were 1.6% and 13.7%. The odd ratios later developed by comparing maternal smoking in pregnancy compared to the control group showed increased association with mother smoking after their first trimester (adjusted OR 1.79, 95 % CI: 1.68–1.92, p < 0.001) and those who smoked in the first trimester (adjusted OR 1.24, 95 % CI: 1.03–1.50, p < 0.012) regarding ADGD development compared to control group. The odd ratio above 1 indicates that the event or condition which is compared would show more likeness to happen in the first group.

The study by Bock et al. (2017) mentions that from a sample of children it is found that with increased experience of stressful events by the children were associated with increased showcase of ADHD symptoms. This study also mentioned that change in posterior internal capsule of the brain are seen among individuals as a result of effect of stressful events which indicates that structural changes in the brain due to stress leads individuals to develop ADHD. The fact is supported by the study of Humphreys et al. (2019) where it is mentioned children who are exposed to stressful life events expressed greater mean ADHD scores with the strongest impact associated with financial problems in the family and the least effect associated with losing someone in the family. Thus, this indicates that familial factors are responsible to raise stress among individuals which in turn affects the brain functioning of the individuals making them show increased symptoms of ADHD.

There are studies which mention that exposure to chemicals such as everyday toxins present in carpeting and flooring, foods, cleaning and lawn products along with personal care products like toothpaste, etc are seen to show contribution in raising the risk of ADHD development among children (Aksoy, 2018). The foetus and children are found to be vulnerable to get affected by the toxins as their biological system are immature and require time to be developed to act effectively in protecting them from the toxic effects (Sciberras et al. 2017). Thus, exposure to even minimum amount of toxins leads to alter the critical juncture within the body of the child making them face hindered brain functioning showing symptoms of ADHD. In the study San Mauro Martín et al. (2018) it is mentioned that nutritional behaviour acts to cause ADHD among children. This is because nutritional deficiency in the body leads to hinder proper functioning of the brain making individuals show antisocial behaviour as a result of hindering thinking ability. The cells in the body require proper amount of amino acids for effective functioning and in particular amino acids such as tyrosine, phenylalanine and tryptophan are required for producing neurotransmitters such as serotonin, dopamine and norepinephrine. The people with ADHD are seen to express issues with the production of the neurotransmitters as well as have low level of amino acids in the blood (Vijayan et al. 2018). This indicated that lack of proper nutrient in the body hinders its functioning making children develop ADHD.

Conclusion

The above discussion informs that Attention Deficit Hyperactive Disorder (ADHD) is a development disorder found mainly in children which have the ability to get extended in adolescent and adulthood. The genetic factors such as VNTRs of DRD4 gene and DAT1gene are found to be responsible for raising the symptoms of ADHD in children. In addition, genetic variations such as deletion or addition of genes in the chromosome along with parental inheritances are responsible genetic factors that lead to ADHD development. The environmental factors such as smoking and stress along with deficiency of nutrients are found to cause ADHD development in children.

References

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