According to the text, there is strong evidence suggesting that Generalized Anxiety Disorder (GAD) is characterized by significant changes in brain anatomy, specifically in areas related to anxiety. These areas, including the amygdala, hippocampus, and prefrontal cortex, can experience long-term shifts. While biological factors like heart rate, blood pressure, cortisol, and BMI may not be reliable indicators, genetic predisposition has been linked to other forms of anxiety disorders. However, the exact causes of anxiety disorders are not fully understood and may differ among age groups, demographics, and genders. Overall, GAD is increasingly being studied and explained through the lens of neurobiology and genetics.