Q. A 7-year-old boy is brought to the physician by his parents because of 2 episodes of jerky movements over the past 3 days. He is at the 12th percentile for height and 45th percentile for weight. His vital signs are normal. On clinical examination, has multiple hyperpigmented nodules on his shoulder with numerous pedunculated lesions over his back. Multiple pigmented nodules in his iris are detected on ophthalmologic examination. Which of the following can also be found in this case?