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Running head: ADHD IN TWINS 1


ADHD In Twins

Barbara Maclure

Keiser University

ADHD in Twins

Research indicates that genes play an integral role in the etiology of ADHD, attention deficit hyperactivity disorder. Genes also affect the disorder’s comorbidity with other disorders. Adoption, family, and twin studies indicate that ADHD can be inherited. Its heritability is rated around seventy four percent and this led to research in susceptibility genes for the condition (Willcutt, 2019). Studies in genetic linkage indicate that there are minimal effects of DNA risk variants on ADHD.

In nature, ADHD is a condition that commences in childhood and works to induce hyperactivity, impulsivity, and inattention. Research over the years has replicated and documented key knowledge on the disorder. It strikes in nearly five percent of children and varies across cultures or geographies. The disorder also tends to occur together with other conditions including substance abuse disorders, learning disorders, conduct disorders, anxiety, and mood disorders. Studies that are longitudinal in nature indicate that over two thirds of children with ADHD carry the disorder into their adult lives (Chen et al., 2018). The disorder increases the risk for numerous functional impairments.

Clinical Course and Features

The clinical course and features of the disorder are as follows.

Psychiatric comorbidity. Numerously variated studies into siblings and twins indicate a general genetic underpinning and feature that impacts the disorder, and numerous other neuropsychiatric disorders. Research indicates that a latent shared genetic feature is attributed for the following. Thirty one percent of covariance in neurodevelopmental symptoms during childhood. Forty five percent of covariance across phobia, internalizing, and externalizing childhood symptoms. Likened results have been reported for diagnoses that are register based and clinical. Studies show that a common genetic factor was accountable for ten to thirty six percent of disorder liability across numerous psychiatric diagnoses. Research indicates that there have been assessments of the contribution of measured genetic variants for a general psychopathology dimension. There were also estimations of SNP heritability that was rated at eighteen percent for maternal rating of total problems, on the checklist for child behavior. This heritability is a metric for attention, externalizing, and internalizing shortcomings (Greven et al., 2016). For a general psychopathology factors, an estimation of thirty eight percent for the SNP heritability was made from assessment of childhood symptoms, by numerous raters.

Developmental effects. The initial twin studies for the disorder utilized self-reported data and made heritability estimates ranging from thirty to forty percent. These estimates are lower than those of adolescents and children. On the other hand, studies indicated heritability to be at an estimated eighty percent when the data was combined with that of parent ratings. For adults clinically diagnosed with the disorder, the heritability was estimated at around seventy two percent. These discoveries indicate that the heritability of the condition remains stable as the individual moves from childhood to adulthood. Measurement errors attributed to rater effects caused previous reports of minimal heritability, for the disorder’s symptoms in adults (Willcutt, 2019). The set of genetic variabilities accounting for the development of the disorder is differentiated to those accounting for its remission and persistence.

Reporter effects. Teacher and parent rating of the disorder and its symptoms lead to increased heritability that is anywhere between seventy and eighty percent. Self-reporting or rating, on the other hand, has lower heritability for adults and adolescents that is at about fifty percent (Gregory et al., 2017). Studies of twins looked into rater effects and found out that different teacher and parent rating, and self-rating led to lower heritability of the disorder.

Genetic Overlaps

Studies into twins have looked in genetic overlaps between ASD, autism spectrum disorders, and ADHD. Research indicates that genetic factors have an impact on this comorbidity with more than zero point five correlation between the two. The same has been observed in adult twins. Studies all over the world indicate that people with ASD and their loved ones are at a higher risk of developing ADHD (Park et al., 2017). The patterns of associativity between relatives reiterated the existence of a genetic overlap between the disorder and ASD that has been clinically ascertained.

Only a few researches have looked into how genetic factors add to the co-occurrence between an internalizing disorder and ADHD. Studies of large families indicated increases in risk for completed and attempted suicide, in second and first degree relatives of the disorder’s probands. Such patterns of familial risk indicate that common genetic underpinnings are important for ADHD and internalizing disorder associations (Elkins et al., 2018). Similar studies with association to depression in families indicate an association that is also caused by shared genetic and familial underpinnings.

Genetic Heterogeneity

There may be genetic heterogeneity that could make it difficult to study multigenerational families. This is due to a high probability of bi-linearity where ADHD genes emanate from both sides of the family, where both parents have these genes and not just one. Additionally, ADHD susceptibility could emanate from different populations who possess different genes. The risk of protection could be conferred by different alleles in the same locus, as in allelic heterogeneity. Incomplete penetrance could also lead the gene variant to fail to cause a phenotype, and this could be another contributing factor. According to studies, ADHD risk alleles can be common variants in populations leading susceptibility being the norm (Agnew-Blais et al., 2018). Other factors could include epistasis and make it difficult to point out the exact cause and method of inheritance of the disorder in families.

Studies of twins play an integral role in the assessment of the contribution of genetic factors on the etiology of the disorder. The approach was formulated to stifle debate on whether environmental or genetic factors can determine behavioral disorders. The theoretical underpinnings of these studies look into dizygotic or DZ twins and monozygotic or MZ twins (Chen et al., 2018). The former share near half of their genes while the latter share all of their genes. Similar diagnoses or phenotypes between both types could, therefore, be instrumental in analyzing the relative importance of genetic factors in ADHD. Theoretically, DZ twins have a zero point five concordance rate while MZ twins have a rate of one. For the former the rate is for a fully penetrating autosomal dominant gene and a further rate of zero point two five, for a similar recessive gene. This is a rarity due to complex genetic inheritance and environmental effects, leading to concordance ranging at these figures. Alternatively concordance could be greater in MZ twins on instances where genetics play a role in the disorder. Numerous studies have been undertaken globally and the concordance rate averages zero point seven six (Barkley, 2015). This indicates that the environment leads to twenty to thirty percent of ADHD while seventy to eighty percent is emanating from genetic factors.

Mental Health Effects

The mental health symptomatology of children heightens the risk for sexual and peer victimization and maltreatment. Research indicates disruptive behaviors such as conduct disorder and ADHD, can lead to increased future risk of exposure to neglect and abuse. Symptoms of the disruptive behaviors including noncompliance, impulsiveness, and aggressiveness, may lead to caregiving problems making children vulnerable to numerous forms of victimization. These findings build on previous findings that indicate that the disorder increases the risk for future neglect or abuse in adolescence. The theories that try to explain this are as follows. The association could be due to the continuation of conduct problems and ADHD symptoms into adult life. This theory only accounts for longitudinal association but fails to elaborate the significance of the association of the disorder’s symptoms, for individuals above eighteen years of age. This means that these individuals with remitted ADHD are at risk for neglect or abuse. The other theory and effect is that on relationships (Johansson et al., 2018). Regardless of the remission of the disorder, it can be the case that presumptions by others on an individual’s behavior are preserving, of relationship patterns that may be difficult to change.

Research indicates that the behavior and temperament of children influence the reactions and responses of others to them. There is also emphasis on the importance of the role of preventive monitoring for children with conduct problems and the disorder. Monitoring works to reduce their risk of harm as their parents could struggle to keep up with the children’s demands and behaviors. This could impact the children’s risk of undergoing adversity. Close monitoring of this risk should be entailed as part of regular assessments, with health professionals (Godinez et al., 2015). Research conducted in the future should look into the part played by possible mediators including distress tolerance and parenting skills.


Agnew-Blais, J. C., Polanczyk, G. V., Danese, A., Wertz, J., Moffitt, T. E., & Arseneault, L. (2018). Young adult mental health and functional outcomes among individuals with remitted, persistent and late-onset ADHD. The British Journal of Psychiatry213(3), 526-534. Retrieved from

Barkley, R. A. (2015). History of ADHD. Retrieved from

Chen, Y. C., Sudre, G., Sharp, W., Donovan, F., Chandrasekharappa, S. C., Hansen, N., … & Shaw, P. (2018). Neuroanatomic, epigenetic and genetic differences in monozygotic twins discordant for attention deficit hyperactivity disorder. Molecular psychiatry23(3), 683. Retrieved from

Elkins, I. J., Saunders, G. R., Malone, S. M., Keyes, M. A., McGue, M., & Iacono, W. G. (2018). Associations between childhood ADHD, gender, and adolescent alcohol and marijuana involvement: A causally informative design. Drug and alcohol dependence184, 33-41. Retrieved from

Godinez, D. A., Willcutt, E. G., Burgess, G. C., Depue, B. E., Andrews-Hanna, J. R., & Banich, M. T. (2015). Familial risk and ADHD-specific neural activity revealed by case-control, discordant twin pair design. Psychiatry Research: Neuroimaging233(3), 458-465. Retrieved from

Gregory, A. M., Agnew-Blais, J. C., Matthews, T., Moffitt, T. E., & Arseneault, L. (2017). Associations between ADHD and sleep quality: Longitudinal analyses from a nationally-representative cohort of twins. Journal of clinical child and adolescent psychology: the official journal for the Society of Clinical Child and Adolescent Psychology, American Psychological Association, Division 5346(2), 284. Retrieved from

Greven, C. U., Merwood, A., van der Meer, J. M., Haworth, C. M., Rommelse, N., & Buitelaar, J. K. (2016). The opposite end of the attention deficit hyperactivity disorder continuum: genetic and environmental aetiologies of extremely low ADHD traits. Journal of Child Psychology and Psychiatry57(4), 523-531. Retrieved from

Johansson, V., Norén Selinus, E., Kuja-Halkola, R., Lundström, S., Durbeej, N., Anckarsäter, H., … & Hellner, C. (2018). The Quantified Behavioral Test Failed to Differentiate ADHD in Adolescents With Neurodevelopmental Problems. Journal of attention disorders, 1087054718787034. Retrieved from

Park, S. H., Guastella, A. J., Lynskey, M., Agrawal, A., Constantino, J. N., Medland, S. E., … & Colodro-Conde, L. (2017). Neuroticism and the overlap between autistic and ADHD traits: findings from a population sample of young adult Australian twins. Twin Research and Human Genetics20(4), 319-329. Retrieved from

Willcutt, E. G. (2019). The Etiology of ADHD in Adolescents. ADHD in Adolescents: Development, Assessment, and Treatment, 36. Retrieved from

Running head: 1

The Benefit of Utilizing Service Dogs as a Form of Therapy for the Treatment of PTSD and Depression Symptoms

Paul E. Richardson

Keiser University

Psychology of Decision Making

Week 6 – Part 2 of 3 Major Project: First Draft Literature Review

December, 2019



Over the most reason years medical professionals have conducted multiple studies on the benefits of utilizing service dogs as a form of therapy for the treatment of PTSD and depression symptoms. There are multiple studies that suggest that service dogs have a tremendous value and can reduce PTSD and depression symptoms. Ultimately there are studies that suggest that there is a need for more in-depth studies to solidify the claim that service dogs can be used as a form of therapy for the treatment of PTSD and depression symptoms.

The Benefit of Utilizing Service Dogs as a Form of Therapy for the Treatment of PTSD and Depression Symptoms

This literature review will be based on ten articles and will highlight similarities between studies that support the thought of service dogs being an alternative form of therapy for the treatment of PTSD and depression symptoms. The three primary section will be based on: service dogs reducing symptoms of PTSD and depression this section will discuss evidence that suggests that service dogs have the ability to reduce PTSD and depression symptoms. Methods used to identify the positive effect of utilizing service dogs as a form of therapy for PTSD and depression symptoms: this section will discuss the various methods used by medical professionals to validate their claim that service dogs can reduce symptoms of PTSD and depression. The last section: the need for further research will discuss the reasoning for conducting more research on the topic to claim that service dogs can reduce the symptoms of PTSD and depression.

Service Dogs Reducing Symptoms of PTSD and Depression

The common theme in the literature was that service dogs have the potential to reduce symptoms and effects of PTSD, depression and elevate the overall quality of life of PTSD suffers. (Thompson-Hollands, et al., 2019) stated that the key to successfully participating in PTSD therapy is a functioning support system. With that being said supporters of utilizing service dogs for the treatment of PTSD and depression symptoms see the primary benefit of the dogs as such; as a support and motivational system. (Kloep , Hunter, & Kertz, 2017) mentioned that the benefit of a service dog reflects in the overall increase of social support and quality of life. (Kloep, et al., 2017) also reported that participants in the study described a significant reductions in PTSD and depression symptoms and a decrease of anger. (Ohaire & Rodriguez, 2018) stated that participants of their study did not report physical improvements based on the service dog but a significant increase in the mental quality of life. Furthermore (Ohaire & Rodriguez, 2018) stated that participants of their study felt an increase of companionship based on the dogs; which in return motivated them to remove themselves from social isolation and to actively engage in social activities. According to (Yarborough, Stumbo, Yarborough, Owen-Smith, & Green, 2018) service dogs not only decreased symptoms of PTSD and depression but also significantly improved the quality of life of the PTSD sufferers. (Yarborough et al., 2018) also stated that this was facilitated by the means of service dogs: reducing hypervigilance which improved relationships, the ability to work, and sleep. Lastly adapting an active lifestyle, increased social participation, and a reduction of suicidal thoughts was also benefits contributed to the service dogs. (Faust, 2016) highlights the benefit of service dogs as not only reducing symptoms of PTSD and depression but also the fact that service dogs provide a sense of companionship. (Faust, 2016) continues to claim that this type of companionship has a positive effect on the emotions of the veteran; and in return leads to an increase in the quality of life. (Rothbaum, 2013) sees a direct correlation between the reduction of PTSD symptoms and the increase in quality of life that service dogs provide. (Rothbaum, 2013) states that service dogs lead PTSD sufferers to be more socially and physically active by reducing avoidance.

Methods Used to Identify the Positive Effect of Utilizing Service Dogs as a Form of Therapy for PTSD and Depression Symptoms

(Kloep , Hunter, & Kertz, 2017) discuss the method utilized in a three week training program using service dogs. The sample consisted of two groups. In order to establish a base line, the participants completed a self-assessment based on PTSD, depression, perception of social support, anger, and overall quality of life one month prior to starting the study. The sample consisted of a total of 13 participants which all have been diagnosed with PTSD prior to starting the study (p.427). Both groups started the study at two different times. The study concluded with a six month follow up. (Ohaire & Rodriguez, 2018) utilized a nonrandomized efficacy trial comparing typical PTSD treatment with a combination of typical treatment and utilizing service dogs. The study included 141 participants (p.179). (Yarborough, Stumbo, Yarborough, Owen-Smith, & Green, 2018) discussed a method that was based on four in-depth interviews and observations of participants during training sessions with their service dogs. Thematic analysis was used in order to characterize the data.

The Need for Further Research

An additional common theme in the literature was the fact that there is a significant need for further research on the topic. (Van Houtert, Endenburg, Wijnker, Rodenburg,&Vermetten, 2018) mentioned that most studies that were conducted on the efficiency of service dogs, were based on the self-perceived wellbeing of individuals. (Van Houtert et al., 2018) furthermore states that it is unclear if dogs could not even be replaced with other animals and yield the same results. Based on the fact that the majority of conducted studies are indirect and anecdotal they do not give clear and precise data. There is also no standardized method used in researching the effect of service dogs, which in return does not provide concreate evidence on the positive effect of service dogs and represents a risk to human participants and animals alike. (Stumbo & Yarborough, 2019) mention the need for in-depth studies utilizing randomized controlled trials comparing veterans that utilize common PTSD treatment therapies and veterans utilizing service dogs. This will be necessary to establish clear and reliable data on the topic. Self-selection bias and excessive expectations for service dogs should be accounted for in future trials. These criteria’s have not been controlled prior in a non-randomized study; and would give a study more validity. The lack of long term follow ups is also an issue that calls for more research on the topic. (Ohaire & Rodriguez, 2018) stated that short- and long-term efficiency based on individual modifications have not been evaluated. Ultimately continues research is needed to identify the most successful method to incorporate service dogs in typical evidence-based treatment options and to optimize service dog practices. (Glintborg & Hansen, 2017) reported that there is a significant need to develop proper training methods that will allow PTSD sufferers to properly learn how to handle a service dog. The fear is that a patient that suffers from PTSD might not experience a relief from PTSD symptoms such as anxiety but even worsen the symptoms based on not knowing how to handle the dog properly. (Gnaulati, 2019) is concerned with the ethical issues that short term symptom reduction in the treatment of PTSD carry. Utilizing such methods can cause patients, caregivers, and the public as a whole to believe that these are the best treatment options when they might not be. (Gnaulati, 2019) beliefs that treatment options should not be generalized but tailored to individual needs of PTSD patients.


After reviewing the literature, it is clear that service dogs do have a significant impact and can be used as a treatment option for PTSD and depression symptoms. It appears that the greatest benefit is based on the relationship and companionship that the service dog offers the patient. This relationship allows the PTSD sufferer to become more social and tremendously enhances the quality life for the individual. One aspect that all methods have in common is that they are based on individual personal feelings of participants. Besides that, each study utilized a different method and approach to gauge and analyze the data that was found. Studies would gain more validity if there would be a standardized method to measure the positive effect of service dogs on the treatment of PTSD and depression. Ultimately there is a significant need for further research on the topic to solidify and quantify the claim that service dogs have a positive impact on the treatment of PTSD and depression symptoms.


Furst, G. (2016). Helping war veterans with posttraumatic stress disorder: Incarcerated individuals’ role in therapeutic animal programs. Journal of Psychosocial Nursing & Mental Health Services, 54(5), 49-57. doi:

Glintborg, C., & Hansen, T. (2017). How Are Service Dogs for Adults with Post Traumatic Stress Disorder Integrated with Rehabilitation in Denmark? A Case Study. Animals7(12), 33. doi: 10.3390/ani7050033

Gnaulati, E. (2019). Potential ethical pitfalls and dilemmas in the promotion and use of American Psychological Association-recommended treatments for posttraumatic stress disorder. Psychotherapy56(3), 374–382. doi: 10.1037/pst0000235

Kloep , M. L., Hunter, R. H., & Kertz, S. J. (2017). ExaminingtheEffectsofaNovelTrainingProgramand UseofPsychiatricServiceDogsforMilitary-RelatedPTSD andAssociatedSymptoms. American Journal of Orthopsychiatry87(4), 425–433. Retrieved from

O’Haire , M. E., & Rodriguez, K. E. (2018). Preliminary Efficacy of Service Dogs as a Complementary Treatment for Posttraumatic Stress Disorder in Military Members and Veterans. Journal of Consulting and Clinical Psychology86(2), 179–188. Retrieved from

Rothbaum, B. O., PhD. (2013). Service dogs in military medicine. Psychiatric Annals, 43(6), 291. doi:

Thompson-Hollands, J., Burmeister, L. B., Rosen, C. S., Odougherty, M., Erickson, E. P. G., & Meis, L. A. (2019). Veterans with poor PTSD treatment adherence: Exploring their loved ones’ experience of PTSD and understanding of PTSD treatment. Psychological Services, 1–12. doi: 10.1037/ser0000389

Stumbo, S. P., & Yarborough, B. J. (2019). Preliminary Evidence Is Promising, but Challenges Remain in Providing Service Dogs to Veterans: Commentary on Preliminary Efficacy of Service Dogs as a Complementary Treatment for Posttraumatic Stress Disorder in Military Members and Veterans (O’Haire & Rodriguez, 2018). American Psychological Association87(1), 118–121. Retrieved from

Van Houtert, E. A. E., Endenburg, N., Wijnker, J. J., Rodenburg , B., & Vermetten, E. (2018). The study of service dogs for veterans with PostTraumatic Stress Disorder: a scoping literature review. European Journal of Psychotraumatology9(3), 1–12. Retrieved from

Yarborough, B. J. H., Stumbo, S. P., Owen-Smith, A., & Green, C. A. (2018). Benefits and Challenges of Using Service Dogs for Veterans With Posttraumatic Stress Disorder. Psychiatric Rehabilitation Journal41(2), 118–124. Retrieved from http//

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