PTH and phenylketonuria: Only 25-OH D was significantly higher in patients with PKU [33.1 ng/mL (26.2–40.3)] than in controls [23.4 ng/mL (17.2–24.9); p < 0.001; r = −0.53], without a significant difference between the groups in PTH plasma concentration [PKU: 27.6 pg/mL (19.6–42.8) vs. Co: 36.16 pg/mL (29.2–40.8); p = 0.089; r = −0.29].