The patients with alkaptonuria and TPO antibody–negative hypothyroidism tended to be older than hypothyroid TPO antibody–positive patients (median, 53 [IQR, 47-58] years vs median, 42 [IQR, 17-57] years; P = .10) and had a smaller thyroid volume (median, 4 [IQR, 3.7-5.6] mL vs median, 14 [IQR, 13.6-14.2] mL; P = .01). The gene discussed is TPO; the disease is hypothyroidism.