In a prospective study of children at risk for GTS, children of two GTS-affected parents had three times greater risk of developing ADHD compared to the children of one affected parent, and two times greater risk of developing either tics, ADHD, or OCD [38]. Third, there is some evidence that comorbid GTS/OCD/ADHD may be heritable. A recent latent class analysis of 952 individuals from 222 GTS families was performed to identify GTS subphenotypes based on diagnoses of GTS, OCD, OC symptoms and ADHD [39]. The investigators identified five classes of categorical GTS subphenotypes, of which only the comorbid GTS/OCD/ADHD class was highly heritable [39]. In addition, 34% of all GTS affected individuals had comorbid OCD and ADHD, while only 10% had comorbid ADHD without OCD [39]. Another study of almost 6,000 GTS affected individuals also found a significant increase in OCD and other psychiatric disorders in individuals with comorbid GTS and ADHD compared to individuals with GTS without ADHD [16]. Finally, individuals with comorbid conditions may exhibit a specific subset of symptoms. The evaluation of GTS symptoms in 410 GTS patients utilizing principal component analysis found that individuals who have GTS comorbid with ADHD or OCD are more likely to
