Attention deficit hyperactivity disorder (ADHD) is a developmental disorder that afflicts approximately 3 to 10% of children. This developmental disorder is typically observed to be associated with over-activity among affected children, as well as other types of spontaneous actions in combination with lack of attention. For the last several years there have been several attempts in determining candidate genes that may be associated with this disorder. To date, modifications in the genes responsible for expressing the dopamine receptors D4 and D5 have been implicated to cause ADHD (Kuntsi and Stevenson, 200`).
There are two general approaches into the investigations of the etiology of ADHD. In terms of genetic approaches, the employment of quantitative trait loci (QTL) analysis has been employed and subsequently served as a reliable tool for gene association. The QTL analysis involves screening of large populations and checking any presence of genetic variants within specific genetics markers that are located along the genetic range, which is commonly around hundreds of kilobases of deoxyribonucleic acid (DNA).
The QTL analysis also determines whether there is any linkage that occurs between two particular markers across generation of a family. Linkage studies using QTL analysis may determine whether a specific DNA region is highly variable or not. The developmental disorder ADHD is generally diagnosed through psychiatric assessment, which includes reviewing a child’s behavior as observed from his actual presence in the clinic for a defined amount of time. During this observation stage, the psychiatrist will identify any evidences that may show that there is some kind of mental impairment in the child’s behavior.
It is thus also important that the input of the parents of the child suspected to have ADHD be incorporated with the psychiatrist’s observation because the parents of the child spend more time with the child and thus may have observed more signs in the child while the psychiatrist may only spend half to an entire hour observing a child in his clinic while at play. The psychiatrist also interviews not only the suspected ADHD child but also the parents, asking whether they have observed any peculiar actions or mannerisms that their child may be shown while at home.
The teacher of a child may also be a good source of information with regards to the suspected ADHD child because the child spends approximately 4 to 6 hours a day at school. In the debate participated by Jay Joseph, Stephen Faraone and Joseph Biederman, the issue of the genetic influence on ADHD was addressed. After reading the details of the debate and performing reading on the genetic influences of ADHD, it should be clear to all that the most difficult medical disorder to be analyzed using genetic means are the psychiatric disorders.
Firstly, psychiatrist disorders and their associated genetic signs are often elusive because of the simple fact that psychiatric disorders are simply hard to diagnose. If ever a diagnosis was indeed established in a straightforward manner, it is still difficult to determine the actual severity of a disease, especially in the case of psychiatric or mental disorders. Unlike other internal medical disorders such as cancer, stages of tumor progression are simply based on the staining of antibodies that are known to specifically hybridize to cancer-associated proteins that are present in the particular cancer tissue.
For example, more Her-2-neu proteins visualized in a breast tissue section means that the patient is at a more progressive stage of breast cancer. Unfortunately, psychiatric disorders do not follow that simple norm. ADHD is not the only psychiatric disorder that is hard to categorize as to the precise level of mental disorder, but actually even mental retardation and even bipolar disorder are difficult to classify in relation to the severity of the disorder in the patient.
Another angle to consider regarding genetics and ADHD is that there is no clear cut line that divides the genetic influences from the environmental effect on the child that results in the symptoms of ADHD. Thus geneticists and psychiatrists alike resort to the employment of twin studies in order to rule of one of the two influences on ADHD. The use of twin studies has been often employed in determining whether mental conditions and disorders are influenced by genetics or the patient’s immediate environment (Kerks et al.
, 2008). There may be pitfalls in these twin studies because the investigator should also keep in mind that there is indeed a connection between genes and the environment. For example, the simplest bacterial setting of using the operon system, which is a genetic system which functions based on the presence of lactose or tryptophan, operates only depending on the presence or absence of lactose. On the other hand, the operon genetic system is disrupted when there is enough lactose in the environment of the bacteria.
The initial lactose molecule initiates the lactose operon to start expressing other proteins that are needed to process this simple sugar, but upon reaching an optimal level within the bacteria, the same lactose molecule binds to the operator region of the lactose operon to shut down the entire system. Once lactose within the bacteria reaches a level that is low, the bound lactose molecule detaches itself from the operator segment, allowing the lactose operon to start working again.
Thus the concept of nature and nurture, applied to ADHD may still remain unclear because it is definitely very hard to identify distinct genetic and environmental influences on this developmental disorder. More twin studies should still be conducted, as well as genetic screening of unique markers that may be associated with ADHD, and psychiatric tools for the assessment and evaluation of ADHD and eventually, once a method is designed that will consolidate all the results that were gathered from these different fields of research, a reliable explanation for the etiology of ADHD may be generated.
References
Derks EM, Hudziak JJ, Dolan CV, van Beijsterveldt TCEM, Verhulst FC and Boomsma DI (2008): Genetic and environmental influences on the relation between attention problems and attention deficit hyperactivity disorder. Behav Genet 38:11–23. Kuntsi J and Stevenson J (2001): Psychological mechanisms in hyperactivity: II. The role of genetic factors. J Child Psychol Psychiatry Allied Discipl 42:211–219.