There is a growing debate on the potential link between screen time and the risk of developing neurodevelopmental disorders such as autism spectrum disorder (ASD) and attention-deficit/hyperactivity disorder (ADHD) in children. According to a new study, excessive screen time may be an early sign of developmental disorders.

ADHD affects a person's language skills, behavior and ability to learn and socialize, while ASD primarily impacts their ability to concentrate, stay still or control impulsive behavior. Many of the symptoms overlap between the two conditions and a person may develop both conditions.

Although the exact cause of these neurodevelopmental disorders is not known, it is believed to be due to a combination of genetics and several other factors such as parental use of alcohol and tobacco, premature delivery, low birth weight and environmental risks such as exposure to lead.

"While long periods of screen time in childhood have been suggested to be a cause of ASD/ADHD, the results of this study suggest that some people may have a genetic disposition to use screens because of ASD," said lead researcher Dr. Nagahide Takahashi in a news release.

According to the study, children with a genetic predisposition to ASD are inclined to spend longer time on screens, more than three to four hours from early childhood. Children with ADHD are likely to increase their screen time as they age, even if their initial screen use was for a limited period.

To determine the genetic susceptibility to ASD and ADHD, theresearchers examined 6.5 million polymorphisms in 437 children. Polymorphisms are variations in DNA sequence that can exist in two or more variant forms among different individuals or populations.

Based on the number and size of these gene variations, they calculated the polygenic risk score associated with ASD/ADHD. It was then compared with the amount of screen time among a sample of children aged 18, 32 and 40 months.

"Overall, those with a genetic risk of ASD were 1.5 times more likely to be in the group with about three hours of screen time per day, and 2.1 times more likely to be in the group with more than four hours of screen time," Takahashi said. "Our results suggest that children at risk of ADHD are at risk of having too much screen time, especially since gaming addiction is common. As screen time tends to be longer for children who are particularly susceptible to ADHD, parents and caregivers should be cautious about it and make a commitment before it becomes a problem."