Genetic Studies on ADHD
Genetic Studies on Attention Deficit Disorder – ADHD show gene alterations that may contribute to ADD ADHD in some children. They are especially looking at the DRD4 dopamine receptor gene.
Familial Genetic Studies show that ADHD runs in families.
For example, a child with an older sibling with ADD ADHD is 300% to 500% more likely to himself have Attention Deficit Disorder than is a child without ADD ADHD siblings.
Twin studies and Adoption studies are also included.
Here are some facts from the NIMH on the genetics of ADHD, and some of the current research:
Epidemiology: In a large sample from the U.S. population, the prevalence of ADHD (male: female ratio) in school-age children was 6.7 percent (5.1:1). Depending on the use of adaptive functioning ratings to define definite maladjustment, prevalence estimates of 6.6 percent and 9.5 percent
Family Studies: Several studies demonstrate that ADHD aggregates in families. The rates in probands' sibs in three older studies ranged from 17 percent to 41 percent, with respective rates in controls' sibs ranging from zero to 8 percent. Rates of childhood ADHD in parents of hyperactive probands in several older studies ranged from 15 percent to 44 percent for fathers and 4 percent to 38 percent for mothers, although one study found no evidence of an increased rate of childhood ADHD in parents of ADHD probands
Twin Studies: Two small twin studies found that 4 of 4 and 3 of 3 MZ twins were concordant for ADHD. A larger twin study reported respective MZ and dizygotic (DZ) probandwise concordance rates of 51 percent and 33 percent, with a heritability estimate of 64 percent.
Adoption Studies: Increased rates of hyperactivity or a history of hyperactivity have been found among both adopted-away sibs of children with ADHD and the biological parents of hyperactive boys compared with controls.
Molecular Genetic Studies: The Tranmission Disequilibrium Test (TDT) was used in a family-based association study to identify an association between ADHD and a specific allele at the dopamine transporter locus on 5p (p = 0.006). Another population-based association study found an association between ADHD and an allele at the dopamine D4 receptor on 11p (p = 0.01).
See our sample of studies below:
Evolutionary Advatages to ADHD ?
Tuning major gene variants conditioning human behavior: the anachronism of ADHD.
* Arcos-Burgos M,
* Acosta MT.
Medical Genetics Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD
New findings suggest that attention deficit and hyperactivity disorder (ADHD) is the most common behavioral variant associated with a mental condition.
ADHD prevalence reaches figures of 18% in populations worldwide. Furthermore, genetic variants conferring susceptibility to develop ADHD are not rare but very frequent and eventually totally fixed in some populations.
These patterns of evolution can be associated with the fact that this behavioral trait had provided selective advantage. However, this behavioral trait is now under scrutiny because of new emerging social necessities.
Recent molecular and clinical evidence supports Thom Hartmann's Hunter-Farmer theory, reaffirming that ADHD might be an anachronic behavioral trait.
PMID: 17467976 [PubMed - as supplied by publisher]
Genetics in ADHD Study with Adoptive Families
Adoptive and Biological Families of Children and Adolescents With ADHD.
Author/s: Susan Sprich
Issue: Nov, 2000
ABSTRACT
Objective: Using an adoption study design, the authors addressed the issue of genetics in attention-deficit hyperactivity disorder (ADHD).
Method: This study examined the rates of ADHD and associated disorders in the first-degree adoptive relatives of 25 adopted probands with ADHD and compared them with those of the first-degree biological relatives of 101 nonadopted probands with ADHD and 50 nonadopted, non-ADHD control probands.
Results: Six percent of the adoptive parents of adopted ADHD probands had ADHD compared with 18% of the biological parents of nonadopted ADHD probands and 3% of the biological parents of the control probands.
Conclusion: Results of this study lend support to the hypothesis that ADHD has a genetic component. J. Am. Acad. Child Adolesc. Psychiatry, 2000, 39(11):1432-1437. Key Words: adoption, attention-deficit hyperactivity disorder, family study.
Find dozens of articles on ADHD at http://www.findarticles.com/
Genetics: Dopamine Transporter Gene
Genetics of Childhood Disorders: XX. ADHD
Part 4: Is ADHD Genetically Heterogeneous?
Author/s: Stephen V. Faraone
Issue: Nov, 2000
Reviews of the literature leave no doubt that genes influence the etiology of attention-deficit/hyperactivity disorder (ADHD) (Faraone et al., 1998).
Notably, twin studies show the heritability of ADHD to be about 0.80, indicating that the effect of genes is substantial.
These genetic epidemiological studies have motivated molecular genetic studies of ADHD that have produced intriguing but conflicting results (Faraone and Biederman, 1998).
Researchers have focused on genes in dopamine pathways because animal models, theoretical considerations, and the effectiveness of stimulant treatment implicate dopaminergic dysfunction in the pathophysiology of the disorder.
Two genes that have been intensively studied are the dopamine transporter gene (DAT) and the dopamine D4 receptor gene (DRD4). Some studies of these genes strongly suggest that they influence susceptibility to ADHD. There are, however, several negative studies for each gene.
The inconsistent results from molecular genetic studies could mean that rather than being a unitary disorder, ADHD comprises several disorders having different genetic and nongenetic etiologies.
See more studies on this topic at FindArticles.com
Recent Findings on Genetics of ADHD
Advances in genetic findings on attention deficit hyperactivity disorder.
* Thapar A,
* Langley K,
* Owen MJ,
* O'donovan MC.
Department of Psychological Medicine, School of Medicine, Cardiff University, Cardiff, UK.
Attention deficit hyperactivity disorder (ADHD) is a common, childhood-onset neurodevelopmental disorder with adverse consequences during adult life.
Family, twin and adoption studies show that genetic factors contribute to the aetiology of ADHD and that environmental factors also play a role.
Family and twin studies have shown the importance of genetic influences on continuity in ADHD over time and in accounting for the co-occurrence of ADHD and conduct disorder problems.
In meta-analyses of molecular genetic studies, the 48-bp variable number tandem repeat (VNTR) variant in the dopamine D4 gene and the CA(n) microsatellite marker in the D5 receptor gene have been found to be repeatedly associated with ADHD.
Results from meta-analyses of the 480-bp VNTR in the dopamine transporter gene are mixed.
Several genetic studies have also identified genetic variants that are related to specific clinical and developmental features of ADHD.
In the next few years, a new generation of much larger-scale genetic studies should lead to the identification of further ADHD susceptibility genes. Such studies will also need to be integrated with other areas of neuroscience, clinical and epidemiological research to investigate how specific gene variants exert risk effects, interact with environmental factors and enable identification of the underlying causal mechanisms that lead to ADHD.
PMID: 17506925 [PubMed - as supplied by publisher]
Twin Study: ADHD and Reading Problems
Understanding comorbidity: A twin study of reading disability and attention-deficit/hyperactivity disorder.
* Willcutt EG,
* Pennington BF,
* Olson RK,
* Defries JC.
University of Colorado at Boulder, Boulder, Colorado.
A community sample of twins in which at least one member of each pair exhibited significant reading difficulties (99 monozygotic and 80 dizygotic pairs) or symptoms of attention-deficit/hyperactivity disorder (ADHD; 83 monozygotic and 78 dizygotic pairs) was used to test the etiology of comorbidity between reading disability (RD) and ADHD.
Univariate analyses revealed moderate to high heritability for all measures of reading difficulty and ADHD.
Subsequent bivariate analyses indicated that the relation between reading difficulties and inattention symptoms is primarily attributable to common genetic influences, whereas bivariate heritability estimates were not significant for hyperactivity-impulsivity and any of the reading measures.
Reading difficulties and ADHD symptoms were more highly heritable if the proband met criteria for both disorders versus RD or ADHD alone, suggesting that future molecular genetic analyses of comorbid RD + ADHD may facilitate the identification of susceptibility genes for RD, ADHD, and their comorbidity. (c) 2007 Wiley-Liss, Inc.
PMID: 17440942 [PubMed - as supplied by publisher]
Where Does Inattention Come From?
Etiology of Inattention and Hyperactivity/impulsivity in a Community Sample of Twins with Learning Difficulties.
Author/s: Erik G. Willcutt
Issue: April, 2000
Erik G. Willcutt [1,3] Bruce F. Pennington [2] John C. DeFries [1]
A community sample of 373 8 to 18 year-old twin pairs in which at least one twin in each pair exhibited a history of learning difficulties was utilized to examine the etiology of inattention and hyperactivity/impulsivity (hyp/imp).
Symptoms of attention-deficit/hyperactivity disorder (ADHD) were assessed by the DSM-III Diagnostic Interview for Children and Adolescents. Inattention and hyp/imp composite scores were created based on results of a factor analysis.
Results indicated that extreme ADHD scores were almost entirely attributable to genetic influences across several increasingly extreme diagnostic cutoff scores.
Extreme inattention scores were also highly heritable whether or not the proband exhibited extreme hyp/imp.
In contrast, the heritability of extreme hyp/imp increased as a linear function of the number of inattention symptoms exhibited by the proband.
This finding suggests that extreme hyp/imp may be attributable to different etiological influences in individuals with and without extreme inatten tion. If this result can be replicated in other samples, it would provide evidence that the hyp/imp symptoms exhibited by individuals with Combined Type ADHD and Predominantly Hyp/Imp Type ADHD may be attributable to different etiological influences.