Attention Deficit Hyperactivity Disorder (ADHD) is one of the most common childhood-onset psychiatric disorder, affecting 1-3% of school-age children. The characteristic hyperactivity is often accompanied by learning and other disorders, making the integration to school environment problematic for these children. The family studies indicate that genetic factors contribute significantly to the etiology of ADHD. In twin studies the heritability estimates vary from 0.7 to 0.8. Searching for genetic risk factors, the allelic variants of polymorphic candidate genes are examined in association studies in ADHD as well as other complex inheritance disorders. Since the majority of the hypotheses explaining the pathophysiology of ADHD assume dysfunction of the dopaminergic neurotransmitter system, most candidate genes are also components of this system. The dopamine transporter (DAT1) determining the synaptic dopamine concentration and the highly polymorphic dopamine D4 receptor (DRD4) are the most often studied candidate genes in ADHD. Some of the polymorphisms are located in the coding region of the gene, resulting in an aminoacid sequence difference in the protein, such as the 48 bp VNTR (Variable Number of Tandem Repeats) in the third exon of the DRD4 gene. The 7-repeat allele of this polymorhpism has been implicated as a risk factor in ADHD. Recently, polymorphisms in the non-coding region of genes are being extensively studied; these could be located either in the 5′ or the 3′ region and effect gene expression. The 10-repeat allele of the 40 bp VNTR in the 3′ region of the DAT1 gene has been associated with ADHD. However, identifying the genetic risk factors of this disorder needs further investigation.
|Translated title of the contribution||Trends in genetic studies of Attention Deficit Hyperactivity Disorder|
|Number of pages||12|
|Publication status||Published - Dec 1 2002|
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