Search

In phenylketonuria (PKU), natural protein intake is thought to increase with age, particularly during childhood and adolescence. Longitudinal dietary intake data are scarce and lifelong phenylalanine tolerance remains unknown. Nine centres managing PKU in Europe and Turkey participated in a retrospective study. Data were collected from dietetic records between 2012 and 2018 on phenylalanine (Phe), natural protein, and protein substitute intake. A total of 1323 patients (age range: 1-57 y; 51% male) participated. Dietary intake data were available on 1163 (88%) patients. Patient numbers ranged from 59 to 320 in each centre. A total of 625 (47%) had classical PKU (cPKU), n = 357 (27%) had mild PKU (mPKU), n = 325 (25%) had hyperphenylalaninemia (HPA), and n = 16 (1%) were unknown. The mean percentage of blood Phe levels within target ranged from 65 ± 54% to 88 ± 49%. When intake was expressed as g/day, the mean Phe/natural protein and protein equivalent from protein substitute gradually increased during childhood, reaching a peak in adolescence, and then remained consistent during adulthood. When intake was expressed per kg body weight (g/kg/day), there was a decline in Phe/natural protein, protein equivalent from protein substitute, and total protein with increasing age. Overall, the mean daily intake (kg/day) was as follows: Phe, 904 mg ± 761 (22 ± 23 mg/kg/day), natural protein 19 g ± 16 (0.5 g/kg/day ± 0.5), protein equivalent from protein substitute 39 g ± 22 (1.1 g/kg/day ± 0.6), and total protein 59 g ± 21 (1.7 g/kg/day ± 0.6). Natural protein tolerance was similar between males and females. Patients with mPKU tolerated around 50% less Phe/natural protein than HPA, but 50% more than cPKU. Higher intakes of natural protein were observed in Southern Europe, with a higher prevalence of HPA and mPKU compared with patients from Northern European centres. Natural protein intake doubled with sapropterin usage. In sapropterin-responsive patients, 31% no longer used protein substitutes. Close monitoring and optimisation of protein intake prescriptions are needed, along with future guidelines specifically for different age groups and severities.

Background: In 2011, a European phenylketonuria (PKU) survey reported that the blood phenylalanine (Phe) levels were well controlled in early life but deteriorated with age. Other studies have shown similar results across the globe. Different target blood Phe levels have been used throughout the years, and, in 2017, the European PKU guidelines defined new targets for blood Phe levels. This study aimed to evaluate blood Phe control in patients with PKU across Europe., Methods: nine centres managing PKU in Europe and Turkey participated. Data were collected retrospectively from medical and dietetic records between 2012 and 2018 on blood Phe levels, PKU severity, and medications., Results: A total of 1323 patients (age range:1-57, 51% male) participated. Patient numbers ranged from 59 to 320 in each centre. The most common phenotype was classical PKU ( n = 625, 48%), followed by mild PKU ( n = 357, 27%) and hyperphenylalaninemia (HPA) ( n = 325, 25%). The mean percentage of blood Phe levels within the target range ranged from 65 ± 54% to 88 ± 49% for all centres. The percentage of Phe levels within the target range declined with increasing age (<2 years: 89%; 2-5 years: 84%; 6-12 years: 73%; 13-18 years: 85%; 19-30 years: 64%; 31-40 years: 59%; and ≥41 years: 40%). The mean blood Phe levels were significantly lower and the percentage within the target range was significantly higher ( p < 0.001) in patients with HPA (290 ± 325 μmol/L; 96 ± 24%) and mild PKU (365 ± 224 μmol/L; 77 ± 36%) compared to classical PKU (458 ± 350 μmol/L, 54 ± 46%). There was no difference between males and females in the mean blood Phe levels ( p = 0.939), but the percentage of Phe levels within the target range was higher in females among school-age children (6-12 years; 83% in females vs. 78% in males; p = 0.005), adolescents (13-18 years; 62% in females vs. 59% in males; p = 0.034) and adults (31-40 years; 65% in females vs. 41% in males; p < 0.001 and >41 years; 43% in females vs. 28% in males; p < 0.001). Patients treated with sapropterin ( n = 222) had statistically significantly lower Phe levels compared to diet-only-treated patients (mean 391 ± 334 μmol/L; percentage within target 84 ± 39% vs. 406 ± 334 μmol/L; 73 ± 41%; p < 0.001), although a blood Phe mean difference of 15 µmol/L may not be clinically relevant. An increased frequency of blood Phe monitoring was associated with better metabolic control ( p < 0.05). The mean blood Phe (% Phe levels within target) from blood Phe samples collected weekly was 271 ± 204 μmol/L, (81 ± 33%); for once every 2 weeks, it was 376 ± 262 μmol/L, (78 ± 42%); for once every 4 weeks, it was 426 ± 282 μmol/L, (71 ± 50%); and less than monthly samples, it was 534 ± 468 μmol/L, (70 ± 58%)., Conclusions: Overall, blood Phe control deteriorated with age. A higher frequency of blood sampling was associated with better blood Phe control with less variability. The severity of PKU and the available treatments and resources may impact the blood Phe control achieved by each treatment centre.