ADHD Gene #4: Dopamine Beta Hydroxylase Gene (DBH), Location: Chromosome 9 (q34)
Dopamine Beta Hydroxylase (DBH) is the fourth gene on our list of ADHD Genes. For humans, it is listed on the 9th Chromosome ("q34" refers to a the specific location on the chromosome for the gene). For a list of the other ADHD genes that are being discussed, please click here.
What makes this DBH such an interesting gene associated with ADHD is the fact that several diseases or disorders that are often comorbid (existing alongside of or with) ADHD also have ties to this gene. Among them are smoking (both in tendency to smoke and the number of cigarettes smoked per day) and suceptibility to migraine headaches. Additionally, there is a suggested genetic linkage between a particular form (allele) of this DBH gene and a built-in resistance to Parkinson's disease. Of somewhat interest is the fact individuals with ADHD are statistically more susceptible to contracting Parkinson's later in life than the rest of the general population.
In studies with mice, an analogous DBH gene has shown to play a strong role in regulating body temperature as well as being a key component in response and sensitivity to common antidepressants including Prozac, Paxil and Zoloft.
A major function of the Dopamine Beta Hydroxylase (DBH) gene is to produce an enzyme of the same name, dopamine beta hydroxylase. This enzyme is responsible for converting the important nervous system chemical dopamine into another important chemical called norepinephrine. Individuals with ADHD often show abnormal levels of one or both of these chemicals (typically on the low side). For this enzyme to function properly, it requires adequate levels of the mineral copper as well as ascorbate (a form of Vitamin C). Deficiencies in either of these two dietary components inhibit this enzyme's effectiveness and produce similar symptoms to a DBH deficiency. It is therefore advisable that ADHD individuals take in adequate levels of both of these key nutrients (roughly 2 mg/day for copper for the average person and at least 60 mg/day for vitamin C).
However, even with adequate intake of these two nutrients, ADHD symptoms can definitely persist. One of many possible causes could be an inherited form of the DBH gene that is statistically linked to ADHD. This can be determined by a personal genetic screening. One allele (form) of this ADHD gene is called the DBH A1 allele. Several studies have shown that there is a significant association between this A1 form and ADHD.
In addition, there is some evidence that another allele (form) of this DBH gene on the 9th human chromosome may also play a role in developing ADHD. This form is called the DBH A2 allele. Although there is a somewhat weaker association between this form of the gene and ADHD than the A1 form, several family studies have shown a notable correlation between the presence this form of the gene and the development of ADHD. Additionally, some research has suggested that the presence of this A2 form of the gene is tied to a parental history of ADHD (often with a higher correlation to the father), and the subtype of ADHD. Some evidence (which has not been repicated extensively) points to a correlation between this A2 form of the gene and an ADHD subtype called the combined subtype.
The combined subtype refers to a subtype that encompasses both the inattentive component and the hyperactive/impulsive component. The inattentive component has been tied to two other "ADHD genes" previously discussed, the DRD4 gene, and the DRD5 gene, while the impulsive/hyperactive component of ADHD which has been associated with another previous post of a gene and its "ADHD form" called the DAT gene.
The next post will soon be up on another "ADHD gene" of topic, the Serotonin Transporter Gene (5-HTT).
For a list of other posts on ADHD Genes, please click here.
Saturday, September 6, 2008