What are the possible abnormalities associated with double Y chromosomes?

Symptoms of XYY chromosome syndrome often manifest as normal phenotype with tall stature, exceeding peers by 0–5 cm. The incidence increases with greater height; among males taller than 2 meters, the occurrence rate is 10%. Patients with XYY chromosome syndrome may present with radioulnar synostosis, severe acne, epileptic seizures, and cardiovascular abnormalities. Most patients have normal intelligence with IQ within the normal range, although a minority may experience delayed speech and language development. It is recommended that patients seek timely medical evaluation and appropriate treatment at a hospital to facilitate recovery.