Scientists and doctors agree that the real cause of attention deficit/hyperactivity disorder (ADHD) is still unknown. General consensus among these communities is that ADHD has a biological nature. Many persons accordingly believe that it results from a chemical imbalance in the brain. The wide use of stimulants, and their subsequent success, to treat ADHD suggests that a difference in composition between the brains of ADHD and non-ADHD people. In the past, researchers have primarily concentrated on two possible causes for this: genetics and environment. New data from a group of international researchers, however, proposes that genetic abnormalities are significant components of ADHD.
Composition of ADHD
A new explanation for ADHD has resulted from a team of researchers based out of Cardiff University, Wales. They have identified an excess of large, rare copy number variants (CNVs) in children with ADHD compared to control participants. Specifically, children with ADHD had more than twice the average number of CNVs. According to researchers, CNVs are pieces of DNA that are either missing or extraneous in the chromosomes. These have also been found to contribute to such neurodevelopment disorders as schizophrenia, epilepsy and autism. The discovery of CNVs prompted researchers to analyze 306 children diagnosed with ADHD but without schizophrenia or autism.
"Our first aim was to examine whether children with ADHD had an increased burden of CNVs compared with controls and to test whether this increase was attributable to associated intellectual disability since ADHD, similarly to autism and schizophrenia, occurs with increased frequency in individuals with intellectual disability," the researchers explained. They then wanted to investigate if CNVs from the ADHD sample were also linked to autism and schizophrenia, as previously implicated.
Results from the Study
One outcome of the study is that specific genes have been identified as underlying factors of ADHD. Experts assure that someone with these genes will not necessarily have ADHD, but rather that they could.
"This tells us that there is a biological marker that tells us that this person is susceptible to develop this disease," stated Dr. Robert Marion, chief of genetics and developmental medicine at the Children's Hospital at Montefiore. The study also suggests a shared biological foundation between ADHD and autism. This is because of the discovery of mutual genetic characteristics. Researchers further found genetic overlaps with schizophrenia. Dr. Marion states that persons can now concede ADHD is "not purely a social construct. It's a real hard and true disorder."
On the other hand, the study does not rule out environmental factors. Researchers continue to speculate that specific environments determine whether a person with the right genetic variations go on to develop ADHD, autism, schizophrenia or nothing at all. Genetic testing may also help determine what people are susceptible to ADHD or other conditions. This can help prepare parents for managing the disorder in their children. Other studies also support that ADHD appears to run in families.
Researchers indicate that between 10 and 35 percent of children with ADHD have a first-degree relative with past or present symptoms. Approximately half of parents who have been diagnosed with ADHD themselves will also have a child with the condition. Finally, studies of twins suggest a genetic element to ADHD. If the disorder is present in one twin, it is significantly more likely to be present in an identical twin than in a fraternal twin. These results are present even when the twins have been raised separately.