25-Hydroxy vitamin D concentration was significantly higher in adults with PKU than that in controls [33.1 ng/mL (26.2–40.3) vs. 23.4 ng/mL (17.2–24.9); p < 0.001], whereas parathyroid hormone concentrations showed no difference [PKU: 27.6 pg/mL (19.6–42.8) vs. Co: 36.1 pg/mL (29.2–40.8); p = 0.089]. The gene discussed is PTH; the disease is phenylketonuria.