In a study published online first and appearing in an upcoming edition of The Lancet, researchers have provided the first direct evidence that attention-deficit/hyperactivity disorder (ADHD) is a genetic condition.
ADHD is a brain development disorder, concluded the authors from the MRC Centre in Neuropsychiatric Genetics and Genomics, and Department of Psychological Medicine and Neurology, Cardiff University, Cardiff, United Kingdom.
For many years, ADHD has been attributed to bad parenting or high-sugar diets, despite a number of factors suggesting genetic factors are at play. For example, the child of a parent with ADHD is more likely to have the condition than a child of a parent without it. And if 1 of a set of identical twins has ADHD, the other twin has a 75% chance of having it.
The study involved genetic analysis of DNA from 366 children with ADHD and 1,047 without the condition.
The researchers found that children with ADHD were more likely to have small DNA segments duplicated or missing than controls. This type of genetic variation is found to be more common in brain disorders. Thus this new study provides the first direct evidence that ADHD is a neurodevelopmental disorder.
Furthermore, they also found significant overlap between these segments, or copy number variations (CNVs), and those linked to autism and schizophrenia. Whilst these disorders are currently thought to be entirely separate, there is some overlap between ADHD and autism in terms of symptoms and learning difficulties. This new research suggests there may be a shared biological basis to the 2 conditions.
The most significant overlap was found at a particular region on chromosome 16 which has been previously implicated in schizophrenia and other major psychiatric disorders and spans a number of genes including one known to play a role in the development of the brain.
“We hope that these findings will help overcome the stigma associated with ADHD,” said lead investigator Anita Thapar, MD, Cardiff University. “Too often, people dismiss ADHD as being down to bad parenting or poor diet. As a clinician, it was clear to me that this was unlikely to be the case. Now we can say with confidence that ADHD is a genetic disease and that the brains of children with this condition develop differently to those of other children.”
“Children with ADHD have a significantly higher rate of missing or duplicated DNA segments compared with other children and we have seen a clear genetic link between these segments and other brain disorders,” said author Nigel Williams, MD, Cardiff University. “These findings give us tantalising clues to the changes that can lead to ADHD.”
Is ADHD a genetic disorder? Having an ancestor with a particular mental illness does not necessarily imply that a family member with the same mental illness has inherited the disease. We often have to distinguish a causal relationship from a correlation, or even environmental factors. A family history of ADHD does put someone at a higher risk, yet these familial relationships are not always strictly implied, especially with our new findings of the possible etiologies of these illnesses.
Is ADHD a Genetic Disorder, if so how did the First Ancestor Acquire ADHD
What was the cause of the illness in the ancestor that passed this gene along? Somewhere in the family of origin somebody had to be first to introduce this illness to the family gene pool and this introduction was therefore not genetic in nature. Mental illness can be brought about by environmental stress, toxins, external forces causing genetic mutations, trauma to the brain. As you can see, there are a myriad of reasons why someone can develop a mental illness. If the ADHD was introduced to the family gene pool from an external source or genetic mutation; wouldn’t it make sense that the same conditions could hold? The progress that is being made in genetics and mental illness is fascinating and offers the possibility of actually curing mental illness in the future, as well as offering better treatment as well. Genetic engineering might be the next break-through in mental health.
The recent study of the genetic link to ADHD was conducted by a team of British scientists who mapped the genes of over 1,400 children. These researchers discovered that children with ADHD were more likely to have small pieces of their DNA missing or duplicated. These abnormalities were located in the same region of the brain where schizophrenia is believed to develop as well as autism, which further contributed to the belief that ADHD is a neuro-developmental condition. Other studies have suggested that inheriting a DAT1 10 allele causes the brain to produce excess quantities of dopamine transporters, which results in less dopamine signaling between neurons.
“ADHD is not caused by a single genetic change, but is likely caused by a number of genetic changes, including CNVs, interacting with as yet unidentified environmental factors,” explained coauthor Kate Langley, MD, Cardiff University. “Screening children for the CNVs that we have identified will not help diagnose their condition. We already have very rigorous clinical assessments to do just that.”
The research team said their findings should help clear up misunderstanding about ADHD, so that affected individuals and their families encounter less stigma. They said their results also show that ADHD is better considered as a neurodevelopmental disorder like autism rather than as a behavioural problem.
As with all mental disorders, the exact cause of attention deficit disorder (ADHD) is unknown, so parents should not blame themselves for this problem. It is likely that many factors play a role in each case of ADHD, very little of which has to do with specific parenting or child rearing skills.
Inevitably, parents will ask themselves “What did I do to cause this?” or “How could I have prevented it?”, but most of the evidence points to genetic factors, environmental facts or brain damage.
Instead, parents should focus on how best to help their child with ADHD. Experts hope that someday, understanding the causes of the condition will lead to effective therapies, and evidence is building on the side of genetic causes for ADHD rather than elements of the home environment. Certain aspects of a child’s environment may, however, affect the symptom severity of ADHD once it is established.
Possible causes of ADHD include:
ADHD has a strong genetic basis in the majority of cases, as a child with ADHD is four times as likely to have had a relative who was also diagnosed with attention deficit disorder. At the moment, researchers are investigating many different genes, particularly ones involved with the brain chemical dopamine. People with ADHD seem to have lower levels of dopamine in the brain.
Children with ADHD who carry a particular version of a certain gene have thinner brain tissue in the areas of the brain associated with attention. Research into this gene has showed that the difference are not permanent, however. As children with this gene grow up, their brains developed to a normal level of thickness and most ADHD symptoms subsided.
“Genetics gives us a window into the biology of the brain. In the future these findings will help unravel the biological basis of ADHD which in turn will help develop new and more effective treatments,” said Dr. Thapar.
In a linked commentary, Peter H Burbach, MD, Department of Neuroscience and Pharmacology, Rudolf Magnus Institute of Neuroscience, University Medical Center Utrecht, Utrecht, the Netherlands, said: “The first gains beyond today’s study might be initial insights into the pathogenesis and neurobiology of brain development as influenced by these genetic variants. This knowledge will eventually enter the clinic and might affect the way people think about and treat neurodevelopmental disorders by accounting for the biological consequence of the specific patient’s genotype.”
SOURCE: The Lancet