An informative new study looks at the role of heredity and the environment in regard to reading ability, mathematics ability, and the behavior associated attention-deficit hyperactivity disorder.
In a study of twins, Lee A. Thompson, Ph.D., and colleagues from Case Western Reserve University found the relationship between ADHD behavior and grades involves a complex mixture of genes and the environment.
Researchers discovered reading was more influenced by genetics, while the environment (the shared background of home and school) has more of an influence on math.
The study, published in Psychological Science, Vol. 21, is the first to take a holistic approach in studying the genetic and environmental influences on reading ability, mathematics ability, and the continuum of ADHD behavior.
“The majority of the twins used in the study don’t have ADHD,” Thompson said. “We are looking at the continuum of the behavioral symptoms of ADHD – looking at individual differences – not a disorder with an arbitrary cutoff.”
This type of continuum is a normal distribution or bell curve, with scores symmetrically distributed about the average and getting much less frequent the farther away a score is from the average. Disability is usually classified as the lower extreme on the normal distribution.
The symptoms of ADHD, according to Thompson, can be described with such a continuum, as can reading and mathematics ability. Only a small percent of individuals fall below the common medical cutoff between ability and disability.
Of particular interest to parents and educators is the discovery that for gifted or disabled individuals “there is no difference in cause, just different expression of achievement.”
Thompson and colleagues analyzed 271 pairs of ten-year-old identical and fraternal twins.
The twins were selected from the Western Reserve Reading and Mathematics Project, a study that began in 2002 with kindergarten and first grade-age twins and has collected data yearly about their math and reading ability.
The study focused on two ADHD symptoms: inattention and hyperactivity –behaviors viewed as extremes of their respective attention and activity continuums.
As part of the study, the mother of the twins rated each child on 18 items such as the child’s ability to listen when spoken to, play quietly, and sit still, to assess attention and activity levels.
A researcher testing each twins’ mathematics and reading ability also rated the twins each year on their attention to tasks and level of hyperactivity. The researchers assessed reading ability by evaluating the twins’ recognition and pronunciation of words and passage comprehension.
They measured the twins’ capacity for mathematics by focusing on the twin’s ability to solve problems, understanding of concepts, computational skills, and the number of computations completed in three minutes.
Researchers analyzed the data from three perspectives: one looked at the overall ADHD behavior, one at the level of attention, and at the activity level. They then determined the similarities in genetic and environmental influence between ADHD symptoms and reading and between the symptoms and mathematics.
In doing so, researchers looked at the individual differences on a given trait within a population; and, how certain traits were related to each other. These measures were broken down into identified components: additive genetic effects, shared environment and non-shared environment.
Researchers found that there are some general genes that influence the symptoms of ADHD simultaneously with reading and mathematics ability – and, some genes that influence each specifically.
Not surprising was the finding that both inattention and hyperactivity were detrimental to academic performance.
However, according to Thompson, genes are not everything.
Interventional approaches should be based on the extent of environmental influence on ADHD behavior, reading ability, and mathematics ability across the entire continuum of expression.
Future research, the researchers said, should focus on the underlying connection between ADHD symptoms and poor academic achievement in order to identify the influences that may alter these often co-occurring outcomes.
Source: Case Western Reserve University