Complex sentence: Many individuals with Tourette's go undiagnosed or never seek medical care, while among those who are seen in specialty clinics, attention-deficit hyperactivity disorder (ADHD) and obsessive--compulsive disorder (OCD) are present at higher rates.
Split into simpler sentences: Many individuals with Tourette's go undiagnosed or never seek medical care. Among those who are seen in specialty clinics, attention-deficit hyperactivity disorder (ADHD) and obsessive--compulsive disorder (OCD) are present at higher rates.