There is no specific percentage as to the likelihood of Gavin also having ADHD, as ADHD is not directly inherited. However, there is a higher likelihood of siblings of individuals with ADHD also being diagnosed with the disorder compared to the general population. The exact probability would depend on various factors such as genetics, environment, and other risk factors. It is important for Gavin to be monitored by a healthcare professional if any symptoms of ADHD are observed.
