What are the personality characteristics of individuals with a double Y chromosome?

Individuals with double Y chromosome syndrome (XYY) usually have normal phenotypes. However, they are typically taller than average, exceeding their peers by 10–15 cm. Some patients may present with radioulnar synostosis, severe acne, epileptic seizures, and cardiovascular abnormalities. Endocrine system changes are generally absent, although in rare cases, underdeveloped genitalia may occur. The majority of affected individuals have normal intelligence, with IQ within the normal range; only a small number exhibit delayed speech and language development.