The siblings of children with attention deficit hyperactivity disorder (ADHD) are three to four times more likely to be diagnosed with the disorder than children in general, a child psychiatry research team at National Taiwan University Hospital said.
The team, led by the director of the hospital’s psychiatry department, Susan Gau (高淑芬), has spent years building a nationwide ADHD family database by collecting data on patients’ longitudinal follow-ups and clinical, neuropsychological, pharmacotherapeutic, brain imaging and genetic study results.
Gau said the data they have collected indicate that 25 to 30 percent of the siblings of children with ADHD also have the disorder — a figure that is three to four times higher than the estimated prevalence of ADHD in general in Taiwan at 7 percent.
Typical symptoms of children with ADHD include inattention, hyperactivity, impulsivity, difficulty controlling their emotions and problems organizing or completing a task, which could have a negative impact on their performance in school and social interaction.
“While some children may be diagnosed to have the disorder like their brother or sister, there are also those who are ‘in-betweens,’ meaning they have not been diagnosed with the condition, but have been identified as ADHD cognitive endophenotypes,” Gau said.
While ADHD is hereditary, it is a clinically and genetically heterogeneous disorder, the team said, meaning the disorder can be caused, independently, by a variety of genetic defects.
Since the symptoms and signs of the disease — phenotype (observable traits) of the acting genes — can be the result of multiple genetic and non-genetic factors acting in concert, psychiatrists are using endophenotype, which can be seen as a biological marker more proximal to the biological etiology of a disease than its signs and symptoms, “to target the possible pathophysiological deficits that combine to create the overall condition of ADHD,” the team said.
Neurocognitive deficits such as those in sustained attention, cognitive impulsivity, reaction time, time perception, visual memory and various executive functions (eg, working memory, cognitive flexibility, planning and problem solving) are proposed by the team to be the endophenotypes of ADHD as they are shared by both children diagnosed with ADHD and their clinically unaffected siblings.
Gau said she did not want to put emphasis on the number of the unaffected siblings that are found with the said neurocognitive deficits, citing problems of labeling and unnecessary fear.
However, when asked about the problem of “overdiagnosis” of ADHD as some experts abroad have feared, Gau said that while the allegations might stand in some countries where family physicians and pediatricians are making ADHD diagnoses, it is not statistically supported in Taiwan, where the disorder is almost always diagnosed by psychiatrists adhering to recognized diagnostic criteria.
“In Taiwan the disorder is actually underreported,” she said. “Only about a third of the affected have sought medical attention.”
Despite a prevalence of about 7 percent, National Health Insurance registration records show only about 2.5 percent of people with ADHD went to see a doctor.
Gau attributed the underdiagnosis partly to Taiwanese’s aversion to taking drugs, especially for children, and the social stigma associated with psychiatric disorders