Attention deficit hyperactivity disorder (ADHD) and genetics
Attention Deficit Hyperactivity Disorder (ADHD) is a neurobehavioral developmental disorder characterized by symptoms of hyperactivity, impulsiveness, and inattention. The disorder exhibits a significant genetic component, with heritability estimates ranging from 75% to 91%. Family studies indicate that individuals with a parent or sibling diagnosed with ADHD are at a higher risk, and twin studies reveal a high concordance rate among identical twins. The expression of ADHD is complex, involving multiple genes that contribute to its development, often related to neurotransmitter systems, particularly dopamine and serotonin. Among the identified genes are those encoding dopamine receptor proteins and transporters, highlighting the biological underpinnings of the disorder. Symptoms can impact various aspects of life, persisting into adulthood and often co-occurring with other mental health issues. Diagnosis typically requires thorough assessments by trained professionals, often incorporating input from family and educational contexts. Effective management may involve a combination of medication and behavioral therapies to enhance functioning and address the challenges associated with ADHD.
Attention deficit hyperactivity disorder (ADHD) and genetics
- ALSO KNOWN AS: ADHD; attention deficit disorder (ADD); hyperkinetic syndrome; hyperkinetic impulse disorder
DEFINITION: Attention deficit hyperactivity disorder (ADHD) is a chronic behavioral disorder. It is behavior that is hyperactive, impulsive, and/or inattentive. This behavior must persist for at least six months and be present in two environments (home, work, or school). ADHD affects children, adolescents, and adults.
Risk Factors
Males and individuals having a parent or sibling with ADHD are at higher risk for this disorder.
Etiology and Genetics
Like other neurobehavioral developmental disorders, such as autism or bipolar affective disorder, ADHD is a complex condition whose expression depends on both genetic and environmental determinants. Genetics appears to be the major contributing factor, with reports of ranging from 75 to 91 percent. In most cases, development of ADHD involves many genes, with each gene providing a small to moderate contribution to the overall phenotype. Twin studies have suggested rates as high as 92 percent in (identical) twins and 33 percent in (fraternal) twins. While there is no consistent pattern of inheritance, 10 to 35 percent of children with ADHD have a first-degree relative who is also affected, and approximately half of the parents with ADHD will have one or more children with the disorder.
Recent studies based in part on deoxyribonucleic acid (DNA) sequence data from the Human Genome Project have identified a number of genes that appear to play contributing roles in the development of ADHD. Many of these are associated with neurotransmitters or other proteins that serve as message carriers in the brain. For example, three different ADHD susceptibility genes are known to specify dopamine receptor proteins (DRD2 at position 11q23.1, DRD4 at position 11p15, and DRD5 at position 4p16), another encodes the dopamine transporter protein (DAT1 at position 5p15), and yet another specifies the dopamine beta-hydroxylase (DBH at position 9q34). Serotonin is another protein, and associated ADHD susceptibility genes include the serotonin 1B receptor gene (HTR1B, at position 6q13) and the serotonin transporter genes SLC6A3 and SLC6A4 (at chromosomal locations 5p15 and 17q11.1-q12, respectively). Five additional ADHD susceptibility genes have been identified: SNAP25 (at position 20p11.2), which encodes the synaptosomal associated protein; ADRA2A (at position 10q24), which specifies the adrenergic alpha-2A acceptor; SCN8A (at position 12q13), which encodes the sodium channel alpha polypeptide; TPH2 (at position 12q21), the gene for tryptophan hydroxylase; and COMT (at position 22q11), which specifies catechol-O-methyltransferase.
Symptoms
All children display some of the symptoms of ADHD. Children with ADHD have symptoms that are more severe and consistent. They often have difficulty in school and with their family and peers. ADHD can last into adulthood. It can cause problems with relationships, job performance, and job retention.
There are two categories of ADHD symptoms described in the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) of the American Psychiatric Association: inattentive (classic ADD) and hyperactive-impulsive. Individuals with inattentive (classic ADD) are easily distracted by sights and sounds, do not pay attention to detail, do not seem to listen when spoken to, make careless mistakes, and do not follow through on instructions or tasks. These individuals also avoid or dislike activities that require longer periods of mental effort, lose or forget items necessary for tasks, and are forgetful in day-to-day activities.
Individuals with the hyperactive-impulsive type of the disorder are restless, fidget, and squirm; run and climb and are unable to stay seated; blurt out answers before hearing the entire question; have difficulty playing quietly; talk excessively; interrupt others; and have difficulty waiting in line or waiting for a turn.
Combined ADHD is the most common type of the disorder; individuals with this type have a combination of the symptoms in the inattentive and hyperactive-impulsive types. In addition, many people with ADHD often have depression, anxiety, conduct disorder, oppositional defiant disorder, learning disorders, and substance abuse.
Screening and Diagnosis
There is no standard test to diagnose ADHD. Diagnosis is done by a trained mental health professional; family and teachers are also involved.
The American Academy of Pediatrics recommends that the following guidelines be used for diagnosis in children six to twelve years of age: Diagnosis should be initiated if a child shows signs of difficulty in school, academic achievement, and relationships with peers and family. During diagnosis, the following information should be gathered directly from parents, caregivers, teachers, or other school professionals: an assessment of symptoms of ADHD in different settings (home and school), the age at which symptoms started, and how much the behavior affects the child’s ability to function. The professional should examine the child for other conditions that might be causing or aggravating symptoms, learning and language problems, aggression, disruptive behavior, depression or anxiety, psychotic symptoms, and personality disorder. In order for a diagnosis of ADHD to be made for children, six symptoms from either or both categories listed in the DSM-5 must be present in two or more of the child’s settings, and must interfere with the child’s ability to function for at least six months. For older adolescents and adults, five of these symptoms must be present. The DSM-5 also specifies that patients must have several of the symptoms before the age of twelve.
Treatment and Therapy
The goal of treatment is to improve the child’s ability to function. Doctors should work with parents and school staff; by working together, they can set realistic goals and evaluate the child’s response.
Treatments include medications that can help control behavior and increase attention span. Stimulants are the most common choice for ADHD; they increase activity in parts of the brain that appear to be less active in children with ADHD. Stimulant medications include methylphenidate (Ritalin, Concerta, Metadate, and Daytrana), dextroamphetamine (Dexedrine), amphetamine (Adderall), and atomoxetine (Strattera). Lisdexamfetamine (Vyvanse) has been approved to treat adults with ADHD; it can also be used to treat children aged six to twelve years.
Parents should talk to their child’s doctor if they have any questions about ADHD medication. There are possible risks with these medications, including cardiovascular events (stroke and heart attack) and psychiatric problems (hearing voices and becoming manic). Because of the rare risk of serious heart problems, the American Heart Association suggests that children have an electrocardiogram (ECG) before starting stimulant medication for ADHD.
Other drugs used to treat ADHD include antidepressants, such as imipramine (Janimine and Tofranil), venlafaxine (Effexor), and bupropion (Wellbutrin). Clonidine (used for Tourette’s syndrome) can treat impulsivity.
Children who take medication and go to behavior therapy do better than those who only use medication. Therapy sessions focus on practicing social and problem-solving skills. Counselors will also teach parents and teachers to help the child through positive reinforcement, which could involve changes in the classroom and in parenting style. Often, daily report cards are exchanged between parents and teachers.
Other tools, like the Disc O’ Sit cushion, may be helpful in improving a child’s attention in class. The Disc O’ Sit is a dome-shaped cushion filled with air, on which the child balances.
Prevention and Outcomes
There are no guidelines for preventing ADHD because the cause is unknown. Proper treatment can prevent problems later in life.
Bibliography
"About ADHD." National Resource Center on ADHD, CHADD, d393uh8gb46l22.cloudfront.net/wp-content/uploads/2018/03/aboutADHD.pdf. Accessed 31 Dec. 2024.
American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders: DSM-5. 5th ed., 2013.
Hughes, Lesley, and Paul Cooper. Understanding and Supporting Children with ADHD: Strategies for Teachers, Parents, and Other Professionals. Chapman, 2007.
McBurnett, Keith, and Linda Pfiffner, editors. Attention Deficit Hyperactivity Disorder: Concepts, Controversies, New Directions. Informa Healthcare, 2008.
Pfeiffer, B., et al. “Effectiveness of Disc ’O’ Sit Cushions on Attention to Task in Second-Grade Students with Attention Difficulties.” American Journal of Occupational Therapy, vol. 62, no. 3, 2008, pp. 274–81.
Rappley, M. D. “Child Practice: Attention Deficit-Hyperactivity Disorder.” New England Journal of Medicine, vol. 352, no. 2, 2005, pp. 165–73.
Riley, Julie. “Attention Deficit Hyperactivity Disorder and Attention Deficit Disorder.” Health Library. EBSCO Information Services, 28 Jan. 2014. Accessed 31 Dec. 2024.
Timimi, Sami, and Jonathan Leo, editors. Rethinking ADHD: From Brain to Culture. Palgrave, 2009.
Walter, Kenny. "Coexisting Conditions Decrease Likelihood of Response to ADHD Medication." HCP Line, 27 July 2022, www.hcplive.com/view/coexisting-conditions-decrease-response-adhd-medications. Accessed 31 Dec. 2024.
"What Is ADHD?" American Psychiatric Association, June 2022, www.psychiatry.org/patients-families/adhd/what-is-adhd. Accessed 31 Dec. 2024.
Zhang, Liuyan, et al. “ADHDgene: A Genetic Database for Attention Deficit Hyperactivity Disorder.” Nucleic Acids Research, vol. 40, no. D1, 2012, pp. D1003–D1009.