Sir.—Herein we describe a boy with Down's syndrome, hyperthyroidism, and hypoparathyroidism, a triad that, to our knowledge, has not been previously reported. Hyperthyroidism in children with Down's syndrome has been described.1 We are aware of only three reports of patients with both hyperthyroidism and hypoparathyroidism.2-4 All three cases were in adults, and none of the patients had Down's syndrome. We performed endocrine studies and antibody assays in the patient and his mother and noted the characteristics of this expanded syndrome.
Patient Report.—At 13 years of age the Patient exhibited the classic features of hyperthyroidism, including exophthalmos. His medical history included trisomy 21, a ventricular septal defect, and delayed motor and neurologic development. The thyroid gland was enlarged. Thyroid function measures were as follows: triiodothyronine (by radioimmunoassay), greater than 15.4 nmol/L (>1000 ng/dL); thyroxine, 364 nmol/L (28.3 μg/dL); and thyrotropin, 2 mU/L (2.0 μU/mL). Thyroid antibody titers