Study of Finnish Cohort Provides Insight into ADHD
> 1/29/2008 11:44:28 AM

In a series of articles published in the Journal of the American Academy of Child and Adolescent Psychiatry, a team of researchers from UCLA examine ADHD in Finnish teenagers. Led by Dr. Susan Smalley, the researchers used data from a longitudinal study of a Finnish cohort to investigate a number of issues associated with ADHD, including the cognitive functioning of teens with ADHD and genetic factors that may contribute to the disorder.

The Northern Finnish birth cohort, which has been studied since 1986, includes over 9,000 subjects. The UCLA researchers examined these subjects when they were between the ages of 16 and 18. Using a standardized survey to identify those who exhibited symptoms of ADHD, they created a subgroup of 457 subjects who were further evaluated for ADHD and other psychiatric disorders. The researchers estimated the prevalence of ADHD within the cohort to be 8.5%. Surprisingly, they noted that although medication is rarely used to treat ADHD in Finland, the appearance of ADHD in the Finnish cohort, including its symptoms, prevalence, and associated conditions, resembled the appearance of ADHD in America, where medication is commonly used. The researchers explain that medications used to treat ADHD are effective in the short-term but may be less effective as a long-term solution. Previous research has already demonstrated that the effectiveness of stimulants as a treatment for ADHD may diminish over time, and more research on this topic is necessary.

To examine the cognitive functioning of subjects with ADHD, the researchers used cognitive and behavioral tests. In particular, they assessed executive function deficits (EFD) in these subjects. EFD refers to deficiencies that affect aspects of cognition and behavior, including memory, attention, and motor skills. Past studies have found that EFDs occur frequently in people with ADHD. In the Finnish cohort, however, only half of the subjects with ADHD also had EFDs. Those with cognitive deficits did not show a greater amount of hyperactivity or inattention when compared to others with ADHD, and the researchers believe that current behavioral tests used to identify cognitive deficits do not effectively separate those with cognitive deficits from those without.

The study also looked at gene variations that the researchers believe may play a role in the development of ADHD. The researchers studied 13 genes, including genes in the dopamine pathways, which previous studies have shown may be involved with ADHD. Using 188 subjects with ADHD and 166 controls, they identified two genes within the dopamine pathways that appeared to increase an individual's risk for ADHD. These genes, called DBH and DRD2, were only studied within this specific cohort, and the researchers stress that the genes probably contributed only minimally to the subjects' risk for ADHD. However, the researchers also view this discovery as further evidence of the involvement of the dopamine pathway in ADHD.

Although this study may be limited because of its focus specifically on Finnish subjects, it still provides us with further information on ADHD and the underlying factors that may contribute to it. Although many aspects of ADHD remain elusive, research will allow us a clearer glimpse into the causes and consequences of this disorder. It is important that we continue to research ADHD and adapt our understanding of it as new information becomes available.

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