Attention-deficit hyperactivity disorder causes
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Charmaine Patel, M.D. [2]
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Overview
Attention deficit hyperactivity disorder is thought to have a strong heritability component. Several genes have been implicated in causing ADHD when occurring together. No single gene alone has been implicated in causing ADHD itself.
Causes
According to a majority of medical research in the United States, as well as other countries, ADHD is today generally regarded as a chronic disorder for which there are some effective treatments, but no true cure.[1] Evidence suggests that hyperactivity has a strong heritable component, and in all probability ADHD is a heterogeneous disorder, meaning that several causes could create very similar symptomology.[2] Candidate genes include dopamine transporter (DAT), dopamine receptor D4 (DRD4), dopamine beta-hydroxylase (DBH), monoamine oxidase A (MAOA), catecholamine-methyl transferase (COMT), serotonin transporter promoter (SLC6A4), 5-hydroxytryptamine 2A receptor (5-HT2A), and 5-hydroxytryptamine 1B receptor (5-HT1B). Researchers believe that a large majority of ADHD arises from a combination of various genes, many of which affect dopamine transporters.[3] Suspect genes include the 10-repeat allele of the DAT1 gene,[4] the 7-repeat allele of the DRD4 gene,[4] and the dopamine beta hydroxylase gene (DBH TaqI).[5]
Genome wide surveys have shown linkage between ADHD and loci on chromosomes 7, 11, 12, 15, 16, and 17.[6] If anything, the broad selection of targets indicates the likelihood that ADHD does not follow the traditional model of a "genetic disease" and is better viewed as a complex interaction among genetic and environmental factors. As the authors of a review of the question have noted, "Although several genome-wide searches have identified chromosomal regions that are predicted to contain genes that contribute to ADHD susceptibility, to date no single gene with a major contribution to ADHD has been identified."[7]
Studies show that there is a familial transmission of the disorder which does not occur through adoptive relationships.[8] Twin studies indicate that the disorder is highly heritable and that genetics contribute about three quarters of the total ADHD population.[8] While the majority of ADHD is believed to be genetic in nature,[8] roughly one-fifth of all ADHD cases are thought to be acquired after conception due to brain injury caused by either toxins or physical trauma prenatally or postnatally.[8]
References
- ↑ NINDS Attention Deficit-Hyperactivity Disorder Information Page. National Institute of Neurological Disorders and Stroke (NINDS/NIH) February 9, 2007. Retrieved on 2007-08-13.
- ↑ Barkley, Russel A. "Attention-Deficit/Hyperactivity Disorder: Nature, Course, Outcomes, and Comorbidity". Retrieved 2006-06-26.
- ↑ Roman T, Rohde LA, Hutz MH. (2004). "Polymorphisms of the dopamine transporter gene: influence on response to methylphenidate in attention deficit-hyperactivity disorder." American Journal of Pharmacogenomics 4(2):83–92 PMID 15059031
- ↑ 4.0 4.1 Swanson JM, Flodman P, Kennedy J, et al. "Dopamine Genes and ADHD." Neurosci Biobehav Rev. 2000 Jan;24(1):21–5. PMID 10654656
- ↑ Smith KM, Daly M, Fischer M, et al. "Association of the dopamine beta hydroxylase gene with attention deficit hyperactivity disorder: genetic analysis of the Milwaukee longitudinal study." Am J Med Genet B Neuropsychiatr Genet. 2003 May 15;119(1):77–85. PMID 12707943
- ↑ M. T. Acosta, M. Arcos-Burgos, M. Muenke (2004). "Attention deficit/hyperactivity disorder (ADHD): Complex phenotype, simple genotype?". Genetics in Medicine. 6 (1): 1–15.
- ↑ M. T. Acosta, M. Arcos-Burgos, M. Muenke (2004). "Attention deficit/hyperactivity disorder (ADHD): Complex phenotype, simple genotype?". Genetics in Medicine. 6 (1): 1–15.
- ↑ 8.0 8.1 8.2 8.3 Barkley, Russell A. Attention-Deficit/Hyperactivity Disorder: Nature, Course, Outcomes, and Comorbidity. ContinuinedEdCourse.Net. Retrieved on 2007-08-12.