Dietary Habits and Metabolic Control in Adolescents and Young Adults with Phenylketonuria: Self-Imposed Protein Restriction May Be Harmful

Abstract

Background: In untreated patients, phenylketonuria (PKU) results in severe encephalopathy with mental retardation. A protein-restricted diet is recommended which can be relaxed in adolescence/adulthood.Methods: We contacted all 72 adult/adolescent PKU patients who had been treated in our center during early childhood. Some still regularly attended our outpatient clinics, while others were lost for follow-up, giving 51 patients in our study. We asked all patients to complete a dietary protocol as well as a questionnaire on quality of life. Blood and urine were analyzed and body impedance plethysmography and cerebral MRI were performed.Results: 42 % of the patients followed protein restriction supplemented with amino acid mixtures (AAM), others had a vegan diet with (8 %) or without (14 %) AAM; 36 % said they were eating normally and did not need any AAM. However, based on dietary protocols and blood urea levels, protein intake was restricted in this patient group. None of the patients examined had serious nutritional deficits. Phenylalanine levels were higher in patients not taking AAM. MRI of the brain was not different from those following protein restriction and taking AAM. The lesions score and mood correlated best with the cumulative phenylalanine values during the first 10 years of life.Conclusion: In summary, 50 % of adult/adolescent patients from our center did not take AAM at the start of our survey although they unknowingly followed selfimposed protein restriction. They had no overt nutritional deficits; however, long-term brain function may be compromised. Our study emphasizes the need for specialized metabolic care in PKU during adulthood.

Effects of Inadequate Amino Acid Mixture Intake on Nutrient Supply of Adult Patients with Phenylketonuria

“…The advised upper limit in Switzerland is 600 μmol/L, which is in accordance with the recently published European guideline [6]. However, many patients with good Phe control in childhood and adolescence will have difficulties to maintain a rigid diet in adulthood [7,8,9,10]. Adults often find it difficult to integrate a strict diet, including regular AAM intake, into social and professional life.…”

“…This study represents the typical situation and real-life setting of an adult PKU clinic, where many patients who stay in regular follow-up principally remain on treatment, but relax their diet (restriction of natural protein, AAM intake) to a variable degree [8,9]. Commonly, patients reduce the amount of AAM, but maintain some dietary protein restriction.…”

The neurological and psychological phenotype of adult patients with early‐treated phenylketonuria: A systematic review

“…However, another study reported abnormalities despite the fact that all patients had adhered to dietary treatment since birth . Additionally, the severity of brain abnormalities were generally associated with historical Phe levels, while there appeared to be no relationship with Phe concentration at the time of MRI evaluation . Furthermore, there was no significant correlations between the volumes of different brain structures and current or historical Phe levels…”

“…Average Phe levels have been reported to be significantly correlated with scores for psychoticism and psychiatric symptom intensity, while better Phe control during childhood was associated with better mood during adulthood . Similarly, depression and anxiety scores were positively correlated with the age at diet initiation and childhood Phe levels, respectively .…”

“…Several studies used standardized QoL tests, which reported good QoL in patients, comparable with that of healthy controls . However, specific QoL domains may be affected in adults with PKU, despite normal scores overall.…”