Vitamin/mineral and micronutrient status in patients with classical phenylketonuria

Background & aims: Strict low-phenylalanine diet is associated with an increased risk of developing micronutrient deficiencies in patients with phenylketonuria (PKU). The primary objective of this single center, case control study was to assess the nutritional parameters of patients with PKU on strict low-phenylalanine diet without vitamin and mineral supplementation compared to a healthy control group. Secondary objective was to identify the adequacy of vitamin/mineral supplementation in phenylalanine-free (Phe-free) amino acid formulas. Methods: A total of 112 age- and sex-matched patients with PKU and 36 controls who did not take vitamin or mineral supplementation at least for the last 6 months were enrolled in the study. Biochemical and hematological markers including hemoglobin, serum vitamin B12, folic acid, iron, ferritin, transferrin saturation, copper, prealbumin, albumin, total protein, phosphorus, calcium, 25-hydroxy vitamin D, zinc, vitamin A and vitamin E levels were screened from fasting morning blood samples. Results: One hundred and twelve patients with classical PKU (53 females, 47.3%) and 36 healthy controls (18 females, 50.0%) were enrolled in the study. The mean age of patients with PKU was 136.8 +/- 82.1 months (18-377). Median serum vitamin B12 level of patients with PKU was found to be higher than the control group (p = 0.002). Vitamin B12 deficiency was 15.2% and 30.6% in patients with PKU and healthy controls, respectively (p = 0.040). Mean serum folic acid level was higher in patients with PKU than the control group (p < 0.0001). In 55.4% of patients with PKU, and 2.8% of the control group, serum folic acid level was above the reference range (p < 0.0001). The frequency of ferritin and prealbumin values above the reference range was found to be higher in patients with PKU compared to the control group (44.4% vs 16.9%, p = 0.001; 38.8% vs 22.1%, p = 0.020, respectively). 25-Hydroxy vitamin D deficiency was detected in 53.6% and 47.2% of patients with PKU and the control group, respectively. Mean serum copper level was higher in the well-controlled (114.3 +/- 26.7 mu g/dL) group than the poorly controlled group (101.0 +/- 29.1 mu g/dL) (p = 0.022). Conclusions: Phe-free amino acid formulas provide adequate vitamin A and zinc levels in patients with PKU, and result in excess folic acid, vitamin B12, copper and vitamin E values that are higher than required levels. Our results demonstrate a high percentage of vitamin D deficiency in patients with classical PKU and also in healthy controls in Turkey. (C) 2018 Elsevier Ltd and European Society for Clinical Nutrition and Metabolism. All rights reserved.