A research team from the National Center of Neurology and Psychiatry, Nara Medical University, and Nagoya University Hospital has uncovered part of the mechanism by which people with attention-deficit hyperactivity disorder (ADHD) later develop Tourette's syndrome.
ADHD is a neurodevelopmental disorder characterized by symptoms such as hyperactivity, impulsivity, and inattention, and is reported to be present in approximately 5% of children. Meanwhile, Tourette's syndrome is a neurodevelopmental disorder characterized by motor and vocal tics that last for more than a year, and is known to have a very high comorbidity rate with ADHD (approximately 1%).
Although there are individual differences, in many cases, ADHD symptoms precede the onset of Tourette's syndrome during childhood, and then appear after adolescence. It has been suggested that ADHD and Tourette's syndrome share common genetic factors, but it was unclear why only a portion of people with ADHD later develop Tourette's syndrome.
In this study, we analyzed pathways involved in both diseases using publicly available data from large-scale whole-genome analyses of ADHD and Tourette's syndrome. As a result, we found that "neutrophil degranulation," a process in which neutrophils, a type of immune cell, release substances inside the body to cause inflammation, is specifically involved in Tourette's syndrome.
We analyzed blood samples from 43 patients with only ADHD and 25 patients with both ADHD and Tourette's syndrome who were treated at Nagoya University Hospital, and found that the neutrophil-lymphocyte ratio (NLR), an indicator of the degree of inflammation, was significantly higher in patients with both conditions.
These results suggest that inflammation may be involved in the onset of Tourette's syndrome, and also suggest that in the future, elevated NLR may become a new biomarker for predicting the risk of developing Tourette's syndrome. Because NLR can be easily measured with a general blood test, it is expected that it will be clinically applied for preventive intervention against Tourette's syndrome.
Paper information:【Brain, Behavior, and Immunity – Health】The role of inflammation in the development of tic symptoms in subjects with ADHD
