A Review of Three Risk Factors for
Attention-Deficit Hyperactivity Disorder






By

Shalyn Schmelter



CHFAM 1500

Professor Day
Introduction

Attention-deficit hyperactivity disorder (ADHD) is a psychological disorder, which includes symptoms of distractibility, disorganization, impulsivity, and sometimes hyperactivity. Experts on ADHD say it afflicts as many as 2.25 million American children or up to 5% of children under 18. The exact cause of ADHD is unknown, but there are several risk factors that have been studied, three of which this paper will explore.
Genetic inheritance of ADHD is explored in a study performed in 1997. This study used twin boys to estimate genetic and environmental contributions to the behavior associated with ADHD. Their findings may help explain some cases of ADHD, but ADHD does not appear to be simply a genetic disorder.
The second study reviewed in this report reviews another possible cause of ADHD. Maternal smoking has been studied as an environmental factor associated with childhood behavior problems including ADHD. This study in 1997 studied 140 children with ADHD and their first-degree biological relatives to review the link between nicotine exposure while in utero and the later development of ADHD.
A third interesting theory reviewed in this report is the possible effect of season of birth and the development of ADHD. A study performed in 1996 investigated the seasonal variations in the birth patterns of children with ADHD. This study proposes that season of birth may be a possible environmental factor that plays a role in the development of ADHD in children and adolescents.
Hopefully, by understanding all possible causes of ADHD, help for children with this disorder will be more effective.

Study 1

Attention-Deficit Hyperactivity Disorder Dimensions:
A Twin Study of Inattention and Impulsivity-Hyperactivity

The subjects of this study were 576 reared-together twin boys, aged 11 and 12 years (average age was 11.8 years). Both monozygotic twins and dizygotic twins were included in the study. Families were excluded if the twins had been adopted or if the twins had physical or intellectual disabilities that would interfere with the day-long assessment. Of the eligible families, approximately nearly 80% completed the assessment.
The research method used in this study was a survey of the twins' teachers and mothers. The teachers completed the MTFS Teacher Rating Form (TRF) which used a 4-point scale to rate subjects' behaviors as "not at all" to "very much". The researchers made an effort to collect reports from more than one teacher by asking the twins and/or their parents to choose three current or recent teachers who were knowledgeable about their school behavior and one other non-teacher adult who would also be able to rate them on non-academic items. Two or more TRFs were completed for each subject and then the scores were averaged.
Reports were also obtained from the mothers of the twins. They completed the Diagnostic Interview for Children and Adolescents-Revised Parent Version (DICA-R). Trained interviewers administered the DICA-R which asked the mother to rate behavior on a three-point scale of "definitely present" to "absent". It was important to obtain reports from more than just the mothers because the mothers' reports showed possible rater bias.
The analysis of the surveys showed that there is evidence of genetic influences on the development of ADHD. Overall, the monozygotic twins showed a high degree of similarity in the surveys conducted. The dizygotic twins showed only a moderate degree of similarity. The researchers conclude that genetic factors are a factor in the expression of ADHD symptoms.

Study 2

Is Maternal Smoking During Pregnancy a Risk Factor For
Attention Deficit Hyperactivity Disorder in Children?

In a study performed in 1996, the role of maternal smoking during pregnancy is reviewed as another risk factor for developing ADHD. The subjects in this survey were 6-17 year old boys with ADHD and normal comparison subjects. A total of 140 children with ADHD and their first-degree biological relatives were compared with the 120 control subjects.
Information on smoking during pregnancy was obtained from the mothers in a standardized manner by raters that did not know the ADHD status of the mother's child. The use of illicit drugs or alcohol use during pregnancy did not differ between the two groups.
The surveys showed that out of the children with ADHD, twenty-two percent had a history of exposure to maternal smoking during pregnancy, compared with eight percent of the control group children. This data shows a significant positive correlation that remained even after adjustment for socioeconomic status, parental IQ and parental ADHD status.
This research indicates that there is a link between maternal smoking during pregnancy and the development of ADHD in children exposed to smoking in utero.

Study 3

Is Season of Birth a Risk Factor for
Attention Deficit Hyperactivity Disorder?

In a 1996 study, researchers investigated the seasonal variations in the birth patterns of children with ADHD in comparison with a group of normal control children. The subjects in this study were 140 boys with ADHD and 120 normal control children. The subjects were similar in age, gender and social class.
The researchers obtained psychiatric data about the children 12 years of age and older from interviews with them and with their mothers. The children younger than 12 years old were not directly interviewed. Interviewers did not know which children were the ADHD subjects.
The season of birth for the ADHD children and control children was evaluated to determine whether in utero winter infections influenced the development of ADHD in children. Although there was no evidence for a strong seasonal pattern of birth in ADHD children, there were peaks for September births in ADHD children who also had learning disabilities and additional psychiatric problems. In addition to the increase in September births for ADHD plus learning disability children, a trend toward an increase in ADHD winter births was also evident.
Researchers hypothesize that first trimester exposure to winter infections may affect the fetus and have an impact on the developing brain. Their findings indicate that winter infections may be associated with ADHD children who also have learning disorders and other psychiatric problems. If season of birth as an ADHD risk factor is studied further, the researchers believe that improved preventative programs could be put in place.

Conclusion
The findings of these three research reports demonstrate that there are many possible risk factors in the development of ADHD in children. While genetic risk factors are the most studied, there are other environmental factors such as maternal smoking and season of birth, which may play a part in the development of ADHD. It is important to investigate the risk factors for this disorder so that prevention and treatment programs can be improved.

ADHD is so prevalent in our society today and affects so many children that we can not afford to dismiss ADHD as solely a genetic disorder.

References Mick, E., Biederman, J. & Faraone, S. (1996). Is Season of Birth a Risk Factor for Attention Deficit Hyperactivity Disorder? Journal of the American Academy of Child and Adolescent Psychiatry 35, 1470-1477.


Milberger, S., Biederman, J., Faranone, S., Chen, L., Jones, J. (1996). Is Maternal Smoking a Risk Factor For Attention Deficit Hyperactivity Disorder in Children? American Journal of Psychiatry 153, 1138-1143.


Sherman, D., Iacono, W., McGue, M. Attention Deficit Hyperactivity Disorder Dimensions: A Twin Study of Inattention and Impulsivity-Hyperactivity. Journal of the American Academy of Child and Adolescent Psychiatry 36, 745-753.