Dietary treatment in phenylketonuria does not lead to increased risk of obesity or metabolic syndrome

Morphofunctional Assessment beyond Malnutrition: Fat Mass Assessment in Adult Patients with Phenylketonuria-Systematic Review

Morphofunctional assessment was developed to evaluate disease-related malnutrition. However, it can also be used to assess cardiometabolic risk, as excess adiposity increases this risk. Phenylketonuria (PKU) is the most prevalent inherited metabolic disease among adults, and obesity in PKU has recently gained interest, although fat mass correlates better with cardiometabolic risk than body mass index. In this systematic review, the objective was to assess whether adult patients with PKU have higher fat mass than healthy controls. Studies of adult PKU patients undergoing dietary treatment in a metabolic clinic reporting fat mass were included. The PubMed and EMBASE databases were searched. Relevance of articles, data collection, and risk of bias were evaluated by two independent reviewers. Ten articles were evaluated, six with a control group, including 310 subjects with PKU, 62 with mild hyperphenylalaninemia, and 157 controls. One study reported a significant and four a tendency towards an increased fat mass in all patients or only females with PKU. Limitations included not having a healthy control group, not reporting sex-specific results and using different techniques to assess fat mass. Evaluation of fat mass should be included in the morphofunctional assessment of cardiometabolic risk in adult patients with PKU.

Dietary intake in individuals with phenylketonuria: an integrative review

Introduction

Introduction: the dietary intake of individuals with phenylketonuria (PKU) may vary widely according to different cultural eating habits, lifestyle, access to multidisciplinary team, and metabolic formulas available. Thus, knowing the dietary intake of this population makes it possible to tailor nutritional treatment strategies to impact their health. Objective: to analyze the evidence on the dietary intake of individuals with PKU. Methods: an integrative literature review was conducted on the dietary intake of individuals with PKU in the databases PUBMED, BIREME and Science Direct. Original articles that addressed the energy and macronutrient food intake of children, adolescents and/or adults with PKU were included in the study, without time restriction, in any language. A total of 384 articles were found and 27 articles were selected and analyzed. Results: evidence about the nutritional composition of their diet showed that individuals with PKU consume between 1160-2721 kcal of energy -7.2-17.4 % (32.4-76.9 g) of energy as protein, 45.9-69.2 % of energy as carbohydrates, 16.6-39 % of energy as lipids- and between 7.6 and 20 g of fiber. Conclusion: most individuals with PKU have low energy, protein and fiber intake, adequate lipid intake, and high carbohydrate intake. Metabolic control of the disease is still a challenge in all countries. Nutritional strategies to improve dietary nutritional composition and phenylalanine blood levels in individuals with PKU remain an urgent issue.

Body Composition Evaluation and Clinical Markers of Cardiometabolic Risk in Patients with Phenylketonuria

Cardiovascular diseases are the main cause of mortality worldwide. Patients with phenylketonuria (PKU) may be at increased cardiovascular risk. This review provides an overview of clinical and metabolic cardiovascular risk factors, explores the connections between body composition (including fat mass and ectopic fat) and cardiovascular risk, and examines various methods for evaluating body composition. It particularly focuses on nutritional ultrasound, given its emerging availability and practical utility in clinical settings. Possible causes of increased cardiometabolic risk in PKU are also explored, including an increased intake of carbohydrates, chronic exposure to amino acids, and characteristics of microbiota. It is important to evaluate cardiovascular risk factors and body composition in patients with PKU. We suggest systematic monitoring of body composition to develop nutritional management and hydration strategies to optimize performance within the limits of nutritional therapy.

Evaluation of the risk factors for noncommunicable diseases in patients with inborn errors of amino acid metabolism receiving nutrition therapy

OBJECTIVES

There is growing concern about the low-protein and high-energy diet therapies used in the treatment of inherited amino acid metabolism disorders. We aimed to identify the risk factors for noncommunicable diseases that may arise from nutritional therapies and suggests approaches that may prevent the development of the noncommunicable diseases.

METHODS

The present study evaluates 112 patients, on long-term nutritional therapy for at least the last 2 years with a diagnosis of an inborn error of the amino acid metabolism, and their 28 healthy siblings. The participants are assessed for the development of overweight and metabolic syndrome based on an analysis of anthropometric parameters, body composition and the results of biochemical tests.

RESULTS

Anthropometric measurements including BMI, weight Z-score, waist circumference and fat mass were not significantly different between patients and controls. Height Z-scores were similar in phenylketonuria patients compared to controls, but lower in urea cycle disorders, organic acidemia and maple syrup urine disease groups. No increased risk of development of overweight or metabolic syndrome was detected in the patient group, while there were findings suggesting malnutrition in patients diagnosed with urea cycle disorders. There was a correlation between patients' BMI and C3-carnitine levels in organic acidemia patients and leucine levels in maple syrup urine disease patients.

CONCLUSIONS

All forms of malnutrition can be prevented in patient groups receiving limited nutrients under a dietary management protocol, based on the findings of anthropometric and biochemical evaluations and analyses of body composition.

Evaluation of the effect of obesity, dietary glycemic index and metabolic profiles on the cardiovascular risk in children with classical phenylketonuria

OBJECTIVES

To compare the glycemic index(GI),obesity,echocardiographic,and arterial stiffness measurements with the healthy control group to evaluate the cardiovascular risk of pediatric classical phenylketonuria(PKU).

METHODS

The study was a prospective observational,involving 104 pediatric volunteers between 2019 and 2020.Two groups were formed:the PKU patient group and the healthy control group.These two groups were further divided into three subgroups:obese,overweight,and normal weight.The patients' anthropometric measurements,body fat analysis,biochemical analysis, GI and glycemic load(GL),arterial stiffness measurements,and echocardiographic findings were recorded.

RESULTS

The PKU patient group's glucose,total cholesterol,LDL,and HDL values were significantly lower than the healthy control group(p = 0.010 for glucose and p = 0.001 for total cholesterol,LDL and HDL).Triglyceride levels were higher in the PKU patient group than in the healthy controls(109.6 vs. 76.7 mg/dl,p = 0.001). GI and GL were significantly lower in the PKU patient group than in the healthy control group(GI 453 vs. 392.9,p = 0.017 and GL 101.1 vs. 85.5,p = 0.036).Left ventricular mass(LVM)-z-score and LVM index were significantly higher in the PKU group than in the healthy control group(LVM z-score 0.9 vs. 0.5,p = 0.014 and LVM index 38.9 vs. 32.7 g/m2.7,p = 0.001). A moderately statistically significant positive correlation was found between the mean phenylalanine(phe) value and pulse wave velocity(PWV) among the PKU patient groups(R: 0.477,p < 0.001).A moderately statistically significant positive correlation was also found between waist circumference and PWV in the PKU patient group(R:0.541, p < 0.001).

CONCLUSIONS

Our study found that close follow-up of phe levels and PWV is more critical than obesity, GI, and GL in the cardiovascular evaluation of classical PKU patients.A large number of multicenter pediatric studies are needed in this area.

Phenylalanine Tolerance over Time in Phenylketonuria: A Systematic Review and Meta-Analysis

In phenylketonuria (PKU), natural protein tolerance is defined as the maximum natural protein intake maintaining a blood phenylalanine (Phe) concentration within a target therapeutic range. Tolerance is affected by several factors, and it may differ throughout a person's lifespan. Data on lifelong Phe/natural protein tolerance are limited and mostly reported in studies with low subject numbers. This systematic review aimed to investigate how Phe/natural protein tolerance changes from birth to adulthood in well-controlled patients with PKU on a Phe-restricted diet. Five electronic databases were searched for articles published until July 2020. From a total of 1334 results, 37 articles met the eligibility criteria (n = 2464 patients), and 18 were included in the meta-analysis. The mean Phe (mg/day) and natural protein (g/day) intake gradually increased from birth until 6 y (at the age of 6 months, the mean Phe intake was 267 mg/day, and natural protein intake was 5.4 g/day; at the age of 5 y, the mean Phe intake was 377 mg/day, and the natural protein intake was 8.9 g/day). However, an increase in Phe/natural protein tolerance was more apparent at the beginning of late childhood and was >1.5-fold that of the Phe tolerance in early childhood. During the pubertal growth spurt, the mean natural protein/Phe tolerance was approximately three times higher than in the first year of life, reaching a mean Phe intake of 709 mg/day and a mean natural protein intake of 18 g/day. Post adolescence, a pooled analysis could only be performed for natural protein intake. The mean natural protein tolerance reached its highest (32.4 g/day) point at the age of 17 y and remained consistent (31.6 g/day) in adulthood, but limited data were available. The results of the meta-analysis showed that Phe/natural protein tolerance (expressed as mg or g per day) increases with age, particularly at the beginning of puberty, and reaches its highest level at the end of adolescence. This needs to be interpreted with caution as limited data were available in adult patients. There was also a high degree of heterogeneity between studies due to differences in sample size, the severity of PKU, and target therapeutic levels for blood Phe control.

Special low protein foods for phenylketonuria in Turkey: An examination of their nutritional composition compared to regular food

Background: Special low protein foods (SLPF) that are phenylalanine (Phe)-free or have a low Phe content are an integral part of PKU diet therapy. Aim: The aim of this study is to determine the nutritional profiles of SLPFs used in Turkey and to compare their contents with equivalent products in the "regular" category, in order to evaluate nutritional and metabolic risks. Methods: Between February and March 2022, the information concerning the nutritional contents of "special low protein products" recommended for PKU and available in Turkey were obtained from the websites of producers/suppliers. Results: A total of 148 SLPFs were identified in Turkey. Compared to regular products, SLPFs were determined to contain less sugar and high carbohydrate content in the Turkish market (p < 0.001). Overall, SLPF products had higher dietary fiber compared to products with regular protein content (p < 0.001). In SLPF subgroups, meat substitutes, rice and pasta, and soup products had significantly less total fat than regular products; low protein bread, sweet snacks, and salted crackers were found to contain less saturated fat (p < 0.05). Moreover, all SLPFs contained significantly more salt than regular products, especially the salt content of subgroups of low protein bread, flour, pasta, and rice was significantly higher than regular products (p < 0.05). Conclusion: Including detailed nutritional information on the Turkish SLPFs' food labels will be effective for patients with PKU to follow themselves on their own.

Glycomacropeptide in PKU-Does It Live Up to Its Potential?

The use of casein glycomacropeptide (CGMP) as a protein substitute in phenylketonuria (PKU) has grown in popularity. CGMP is derived from κ casein and is a sialic-rich glycophosphopeptide, formed by the action of chymosin during the production of cheese. It comprises 20–25% of total protein in whey products and has key biomodulatory properties. In PKU, the amino acid sequence of CGMP has been adapted by adding the amino acids histidine, leucine, methionine, tyrosine and tryptophan naturally low in CGMP. The use of CGMP compared to mono amino acids (L-AAs) as a protein substitute in the treatment of PKU promises several potential clinical benefits, although any advantage is supported only by evidence from non-PKU conditions or PKU animal models. This review examines if there is sufficient evidence to support the bioactive properties of CGMP leading to physiological benefits when compared to L-AAs in PKU, with a focus on blood phenylalanine control and stability, body composition, growth, bone density, breath odour and palatability.

Overweight/obesity in adolescents with phenylketonuria: protective and predisposing factors

OBJECTIVE

To estimate the prevalence and factors associated with overweight/obesity development in adolescents with early diagnosed phenylketonuria treated exclusively by diet.

METHODOLOGY

In this cross-sectional study anthropometric measurements, serum phenylalanine levels, and 10 metabolites associated with lipid and carbohydrate metabolism were analyzed in 101 adolescents aged 10-20 years. Adolescents were categorized into overweight/obesity and eutrophic/low body mass index groups. These patients were compared using Student's t-test, Pearson's chi-square test, Wald's chi-square test for multivariate analysis. Further, to verify whether the prevalence of overweight/obesity found in the study population was similar to that in the general population, the authors compared the nutritional status of 46 patients aged 13-17 years with that of healthy students of the same age from the National School Health Survey using the chi-square test for adherence. The significance threshold was p < 0.5.

RESULTS

The prevalence of overweight/obesity in adolescents was 27.7%. There was no difference in prevalence between sexes. Older age was a protective factor and Increased Homeostasis Model Assessment Insulin Resistance index and high phenylalanine and low-density lipoprotein cholesterol levels were predictive factors for overweight/obesity. The equality hypothesis was not rejected in the comparison of nutritional states of 46 patients aged 13-17 years and healthy students of the same age.

CONCLUSION

The prevalence of overweight/obesity in phenylketonuria adolescents was similar to what is found in healthy adolescents.

The Impact of Phenylketonuria on Body Composition in Adults

INTRODUCTION

Patients with phenylketonuria (PKU) must follow a lifelong phenylalanine (Phe)-restricted diet with additional amino acid supplementations, and this may put them at risk for nutritional disturbances. However, the body composition and nutritional status of adult patients with PKU has only been partially explored. The current study aims to assess the body composition of adult patients with PKU using multifrequency bioimpedance analysis (MF-BIA) and to reveal potential correlations between therapy adherence and body composition. Additionally, we compared body composition of patients with healthy controls.

METHODS

Fifty adult patients with early-treated PKU (27 female and 23 male) and 40 healthy, age- and gender-matched controls were included in this single-center, cross-sectional study. MF-BIA was performed on all subjects. Additionally, we determined serum nutritional markers for all patients. In the PKU patient group, correlation analyses were performed between body composition parameters and therapy adherence. We compared body composition of patients with PKU and controls using BIA.

RESULTS

The proportion of overweight was 56% among all patients with PKU. Female patients with PKU had significantly higher body fat percentage compared with controls. In parallel with higher fat content, we observed lower muscle mass, protein, and mineral content among female patients with PKU compared to controls. Such findings were not observed in male patients. Female patients with PKU had decreased therapy adherence and had significantly lower prealbumin levels compared with males. There was no significant correlation observed between body composition parameters and therapy adherence over the last 10 years in the PKU patient group.

CONCLUSION

Although female patients had less optimal therapy adherence over the last 10 years compared with male patients, our results suggest that this does not influence body composition fundamentally. Our results suggest that obesity is an important comorbidity in young adult patients with PKU, especially in females. We advocate that nutritional assessments and weight management should be additional objectives of PKU management to provide optimal care.

Mechanisms of obesity in children and adults with phenylketonuria on contemporary treatment

BACKGROUND & AIMS

Obesity prevalence in people with phenylketonuria (PKU) is comparable to that of the general population but the underlying aetiology remains unknown. To assess body composition, dietary intake, moderate physical activity duration (MPAD) and energy expenditure (MPAEE), resting metabolic rate (RMR), diet-induced thermogenesis (DIT), fasting and postprandial fat (FOx) and carbohydrate oxidation (CHOOx), in PKU people and healthy Controls.

METHODS

Participants were PKU people (n = 16) and healthy controls (n = 15). Body composition was measured with stable isotopes using deuterium as tracer, dietary intake from 4-day food diaries, MPAD and MPAEE from 7-day activity counts measured by triaxial accelerometers, calibrated against individual rates of oxygen consumption and carbon dioxide production, RMR, DIT, FOx and CHOOx by indirect calorimetry.

RESULTS

Body composition, DIT, FOx, CHOOx and RMR did not differ between the PKU and the Control groups. MPAD (PKU, 73 ± 26 min/week; Control, 152 ± 43 min/week) and MPAEE (PKU, 404 ± 127 kcal/week; Control, 741 ± 153 kcal/week) were lower (P < 0.05) in the PKU than the Control group. Raised phenylalanine levels were inversely related with MPAD and MPAEE. Energy intake and energy provided by protein did not differ between the groups, while energy proportion obtained from carbohydrate was higher (PKU, 60 ± 2%; Control, 51 ± 2%; P < 0.05) and from fat lower (PKU, 24 ± 2%; Control, 35 ± 3%; P < 0.05) in the PKU than in the Control group.

CONCLUSION

People with PKU spent less time and expend less energy in moderate physical activity and have a higher intake of energy from CHO which may be involved in the underlying mechanisms of obesity in PKU.

Is the Phenylalanine-Restricted Diet a Risk Factor for Overweight or Obesity in Patients with Phenylketonuria (PKU)? A Systematic Review and Meta-Analysis

Although there is a general assumption that a phenylalanine (Phe)-restricted diet promotes overweight in patients with phenylketonuria (PKU), it is unclear if this presumption is supported by scientific evidence. This systematic review aimed to determine if patients with PKU are at a higher risk of overweight compared to healthy individuals. A literature search was carried out on PubMed, Cochrane Library, and Embase databases. Risk of bias of individual studies was assessed using the Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies, and the quality of the evidence for each outcome was assessed using the NutriGrade scoring system. From 829 articles identified, 15 were included in the systematic review and 12 in the meta-analysis. Body mass index (BMI) was similar between patients with PKU and healthy controls, providing no evidence to support the idea that a Phe-restricted diet is a risk factor for the development of overweight. However, a subgroup of patients with classical PKU had a significantly higher BMI than healthy controls. Given the increasing prevalence of overweight in the general population, patients with PKU require lifelong follow-up, receiving personalised nutritional counselling, with methodical nutritional status monitoring from a multidisciplinary team in inherited metabolic disorders.

Protein status of people with phenylketonuria: a scoping review protocol

INTRODUCTION

Phenylketonuria (PKU) is a disorder of protein metabolism resulting in an accumulation of phenylalanine in the body. Dietary management consists of altering the sources of ingested protein to limit phenylalanine intake. Current dietary protein guidelines for PKU are based on limited scientific evidence, thus it remains unclear whether current practice leads to optimal protein status in people with PKU. To date, no attempt has been made to systematically evaluate the protein status of people with PKU, using a combination of validated anthropometric, biochemical and functional measurement tools. Furthermore, factors known to influence protein status in the general population warrant consideration when determining protein status in individuals with PKU, alongside factors unique to PKU such as the type of protein substitute consumed. Understanding the impact of these variables on protein status is crucial to developing a personalised approach to protein recommendations for optimising health and functional outcomes in people with PKU. Therefore, the aim of this scoping review is to examine existing evidence regarding the protein status of people with PKU, and to investigate the nutritional and lifestyle variables that influence protein status.

METHODS AND ANALYSIS

This review will be guided by Arksey and O'Malley's framework, along with guidance from Levac et al, Pawliuk et al and the Joanna Briggs Institute. The following databases will be searched: MEDLINE (Ovid), Embase, CENTRAL, Web of Science and Scopus, alongside grey literature. Identified literature will be assessed by two independent reviewers for inclusion. Descriptive numerical analysis will be performed and a narrative summary will accompany the tabulated results describing how study findings relate to the review questions.

ETHICS AND DISSEMINATION

This review protocol does not require ethical approval. Findings will be disseminated through peer-reviewed publication, presented at relevant conferences, and shared with a patient research advisory group to inform discussions on future research.

Cardiac Magnetic Resonance Reveals Incipient Cardiomyopathy Traits in Adult Patients With Phenylketonuria

Background Phenylketonuria is the most common inborn error of amino acid metabolism, where oxidative stress and collateral metabolic abnormalities are likely to cause cardiac structural and functional modifications. We aim herein to characterize the cardiac phenotype of adult subjects with phenylketonuria using advanced cardiac imaging. Methods and Results Thirty-nine adult patients with phenylketonuria (age, 30.5±8.7 years; 10-year mean phenylalanine concentration, 924±330 µmol/L) and 39 age- and sex-matched healthy controls were investigated. Participants underwent a comprehensive cardiac magnetic resonance and echocardiography examination. Ten-year mean plasma levels of phenylalanine and tyrosine were used to quantify disease activity and adherence to treatment. Patients with phenylketonuria had thinner left ventricular walls (septal end-diastolic thickness, 7.0±17 versus 8.8±1.7 mm [P<0.001]; lateral thickness, 6.1±1.4 versus 6.8±1.2 mm [P=0.004]), more dilated left ventricular cavity (end-diastolic volume, 87±14 versus 80±14 mL/m² [P=0.0178]; end-systolic volume, 36±9 versus 29±8 mL/m² [P<0.001]), lower ejection fraction (59±6% versus 64±6% [P<0.001]), reduced systolic deformation (global circumferential strain, -29.9±4.2 % versus -32.2±5.0 % [P=0.027]), and lower left ventricular mass (38.2±7.9 versus 47.8±11.0 g/m² [P<0.001]). T1 native values were decreased (936±53 versus 996±26 ms [P<0.001]), with particular low values in patients with phenylalanine >1200 µmol/L (909±48 ms). Both mean phenylalanine (P=0.013) and tyrosine (P=0.035) levels were independently correlated with T1; and in a multiple regression model, higher phenylalanine levels and higher left ventricular mass associate with lower T1. Conclusions Cardiac phenotype of adult patients with phenylketonuria reveals some traits of an early-stage cardiomyopathy. Regular cardiology follow-up, tighter therapeutic control, and prophylaxis of cardiovascular risk factors, in particular dyslipidemia, are recommended.

The Pah-R261Q mouse reveals oxidative stress associated with amyloid-like hepatic aggregation of mutant phenylalanine hydroxylase

Phenylketonuria (PKU) is caused by autosomal recessive variants in phenylalanine hydroxylase (PAH), leading to systemic accumulation of L-phenylalanine (L-Phe) that may reach neurotoxic levels. A homozygous Pah-R261Q mouse, with a highly prevalent misfolding variant in humans, reveals the expected hepatic PAH activity decrease, systemic L-Phe increase, L-tyrosine and L-tryptophan decrease, and tetrahydrobiopterin-responsive hyperphenylalaninemia. Pah-R261Q mice also present unexpected traits, including altered lipid metabolism, reduction of liver tetrahydrobiopterin content, and a metabolic profile indicative of oxidative stress. Pah-R261Q hepatic tissue exhibits large ubiquitin-positive, amyloid-like oligomeric aggregates of mutant PAH that colocalize with selective autophagy markers. Together, these findings reveal that PKU, customarily considered a loss-of-function disorder, can also have toxic gain-of-function contribution from protein misfolding and aggregation. The proteostasis defect and concomitant oxidative stress may explain the prevalence of comorbid conditions in adult PKU patients, placing this mouse model in an advantageous position for the discovery of mutation-specific biomarkers and therapies.

Plasma Phospholipidomic Profile Differs between Children with Phenylketonuria and Healthy Children

Phenylketonuria (PKU) is a disease of the catabolism of phenylalanine (Phe), caused by an impaired function of the enzyme phenylalanine hydroxylase. Therapeutics is based on the restriction of Phe intake, which mostly requires a modification of the diet. Dietary restrictions can lead to imbalances in specific nutrients, including lipids. In the present study, the plasma phospholipidome of PKU and healthy children (CT) was analyzed by hydrophilic interaction liquid chromatography-tandem mass spectrometry and gas chromatography-mass spectrometry. Using this approach, 187 lipid species belonging to nine different phospholipid classes and three ceramides were identified. Principal component analysis of the lipid species data set showed a distinction between PKU and CT groups. Univariate analysis revealed that 146 species of phospholipids were significantly different between both groups. Lipid species showing significant variation included phosphatidylcholines, containing polyunsaturated fatty acids (PUFA), which were more abundant in PKU. The high level of PUFA-containing lipid species in children with PKU may be related to a diet supplemented with PUFA. This study was the first report comparing the plasma polar lipidome of PKU and healthy children, highlighting that the phospholipidome of PKU children is significantly altered compared to CT. However, further studies with larger cohorts are needed to clarify whether these changes are specific to phenylketonuric children.

METABOLIC CONTROL AND BODY COMPOSITION OF CHILDREN AND ADOLESCENTS WITH PHENYLKETONURIA

OBJECTIVE

To characterize metabolic control and verify whether it has any relation with socioeconomic, demographic, and body composition variables in children and adolescents with phenylketonuria (PKU) diagnosed in the neonatal period.

METHODS

This cohort study collected retrospective data of 53 phenylketonuric children and adolescents. Data on family income, housing, and mother's age and schooling level were collected, and anthropometric measures of body composition and distribution were taken. All dosages of phenylalanine (Phe) from the last five years (2015-2019) were evaluated and classified regarding their adequacy (cutoffs: 0-12 years: 2-6 mg/dL; 12-19 years: 2-10 mg/dL). Adequate metabolic control was considered if ≥7%) of the dosages were within desired ranges.

RESULTS

The mean (±standard deviation) age in the last year was 10.1±4.6 years. Most of them were under 12 years old (33/53; 62.3%) and had the classic form of the disease (39/53; 73.6%). Better metabolic control was observed among adolescents (68.4 versus 51.4%; p=0.019). Overweight was found in 9/53 (17%) and higher serum Phe levels (p<0.001) were found in this group of patients. Metabolic control with 70% or more Phe level adequacy decreased along with the arm muscle area (AMA) (ptendency=0.042), being 70.0% among those with low reserve (low AMA), and 18.5% among those with excessive reserve (high AMA).

CONCLUSIONS

Adequate metabolic control was observed in most patients. The findings suggest that, in this sample, the levels of phenylalanine may be related to changes in body composition.

A 3 Year Longitudinal Prospective Review Examining the Dietary Profile and Contribution Made by Special Low Protein Foods to Energy and Macronutrient Intake in Children with Phenylketonuria

The nutritional composition of special low protein foods (SLPFs) is controlled under EU legislation for 'Foods for Special Medical Purposes (FSMP)'. They are designed to meet the energy needs of patients unable to eat a normal protein containing diet. In phenylketonuria (PKU), the macronutrient contribution of SLPFs has been inadequately examined.

AIM

A 3-year longitudinal prospective study investigating the contribution of SLPFs to the macronutrient intake of children with early treated PKU.

METHODS

48 children (27 boys) with a mean recruitment age of 9.3 y were studied. Semi-quantitative dietary assessments and food frequency questionnaires (FFQ) were collected three to four times/year for 3 years.

RESULTS

The mean energy intake provided by SLPFs was 33% (SD ± 8), and this figure was 42% (SD ± 13) for normal food and 21% (SD ± 5) for protein substitutes (PS). SLPFs supplied a mean intake of 40% carbohydrate (SD ± 10), 51% starch (SD ± 18), 21% sugar (SD ± 8), and 38% fat (SD ± 13). Fibre intake met 83% of the Scientific Advisory Committee on Nutrition (SACN) reference value, with 50% coming from SLPFs with added gums and hydrocolloids. Low protein bread, pasta and milk provided the highest energy contribution, and the intake of sweet SLPFs (e.g., biscuits, cakes, and chocolate) was minimal. Children averaged three portions fruit/vegetable daily, and children aged ≥ 12 y had irregular meal patterns.

CONCLUSION

SLPFs provide essential energy in phenylalanine restricted diets. Optimising the nutritional quality of SLPFs deserves more attention.

Dietary intake and nutritional status of patients with phenylketonuria in Taiwan

Phenylalanine hydroxylase (PAH) deficiency leads to phenylalanine accumulation and results in phenylketonuria (PKU). Phenylketonuria can contribute to severe inability such as mental impairment. Early diagnosis and dietary intervention can have beneficial effects on maintaining normal neural and cognitive function in patients with PKU. However, a long-term low phenylalanine diet may put children at risk of malnutrition. A food supplement was therefore used for children with PKU under dietician supervision according to dietary reference intakes (DRIs). In this cross-sectional study, we enrolled patients with PKU and age-matched controls to compare their anthropometry data [weight, height, body mass index (BMI), and body composition using bioelectrical impedance analysis (BIA)], and correlated it with their dietary intake based on 24-h dietary recall. For continuous parameters, the data were expressed as median ± standard deviation (SD), and the Mann–Whitney U test was used to test the difference among the groups. Correlation by natural proteins, body fat, and fat-free mass were evaluated using the Pearson correlation coefficient. Twenty-two participants diagnosed with PKU (ages 8–27 years; mean 15.23 ± 5.23) and a control group of 22 non-PKU participants (ages 8–39 years; mean 19.73 ± 10.6) were recruited for this study. Between the two groups of participants, no significant difference was found in height, weight, BMI, muscle mass, or fat mass. The percentage of natural protein has no effect on body composition. We found a significant positive correlation between the total protein intake percentage of DRIs and muscle mass (r = 0.491, p = 0.020) and a significant negative correlation in the total protein intake percentage of DRIs and fat mass (r = -0.475, p = 0.025) in participants with PKU. There were no significant differences in body composition and nutrition intake between patients with PKU (under metabolic control) and healthy subjects. Thus, giving proper nutrition treatment may have beneficial effects on body growth and nutrition status in patients with PKU in Taiwan.

Anthropometry and bone mineral density in treated and untreated hyperphenylalaninemia

Despite recent improvements in the composition of the diet, lower mineral bone density and overweight tendencies are incoherently described in patients with phenylketonuria (PKU). The impact of dietary factors and plasma phenylalanine levels on growth, BMI, body composition, and bone mineral density was investigated in our cohort of patients with hyperphenylalaninemia (HPA) with or without dietary treatment. The anthropometric, metabolic, BMI and other nutritional indicators and bone mineral density were compared between the group of 96 treated patients with PKU (58 classic PKU (cPKU) and 38 patients with moderate-mild PKU defined as non-classic PKU (non-cPKU)) and the untreated group of 62 patients with benign HPA. Having compared the treated and untreated groups, there were normal outcomes and no statistically significant differences in BMI, body composition, and bone mineral density. Lower body height standard deviation scores were observed in the treated as compared to the untreated group (P < 0.001), but the difference was not significant when analyzing patients older than 18 years; however, cPKU adults were shorter compared to non-cPKU treated adults (P = 0.012). Interestingly, the whole-body fat was statistically higher in non-cPKU as compared to cPKU patients. In conclusion, the dietary treatment ensured adequate nutrition without significant consequences in BMI, body composition, and bone mineral density. A low protein diet may have delayed the growth in childhood, but the treated patients gained a normal final height. Mild untreated hyperphenylalaninemia characteristic for benign HPA had no negative physiological effect on bone mineral density.

Special Low Protein Foods in the UK: An Examination of Their Macronutrient Composition in Comparison to Regular Foods

Special low protein foods (SLPFs) are essential in a low phenylalanine diet for treating phenylketonuria (PKU). With little known about their nutritional composition, all SLPFs on UK prescription were studied (n = 146) and compared to equivalent protein-containing foods (n = 190). SLPF nutritional analysis was obtained from suppliers/manufacturers. Comparable information about regular protein-containing foods was obtained from online UK supermarkets. Similar foods were grouped together, with mean nutritional values calculated for each subgroup (n = 40) and percentage differences determined between SLPFs and regular food subgroups. All SLPF subgroups contained 43-100% less protein than regular foods. Sixty-three percent (n = 25/40) of SLPF subgroups contained less total fat with palm oil (25%, n = 36/146) and hydrogenated vegetable oil (23%, n = 33/146) key fat sources. Sixty-eight percent (n = 27/40) of SLPF subgroups contained more carbohydrate, with 72% (n = 105/146) containing added sugar. Key SLPF starch sources were maize/corn (72%; n = 105/146). Seventy-seven percent (n = 113/146) of SLPFs versus 18% (n = 34/190) of regular foods contained added fibre, predominantly hydrocolloids. Nine percent of SLPFs contained phenylalanine > 25 mg/100 g and sources of phenylalanine/protein in their ingredient lists. Stricter nutritional composition regulations for SLPFs are required, identifying maximum upper limits for macronutrients and phenylalanine, and fat and carbohydrate sources that are associated with healthy outcomes.

Nutrient intake, body composition, and blood phenylalanine control in children with phenylketonuria compared to healthy controls

Background

Phenylketonuria (PKU) treatment consists of life-long protein restriction and Phe-free medical foods for adequate nutritional intake and growth. A relationship between body composition and blood phenylalanine (Phe) concentrations in subjects with PKU has been proposed but this has not been consistently reported.

Methods

Dietary intake, lean body mass (LBM) and fat mass (FM) were measured in 30 pediatric subjects with PKU compared to 30 age, and sex matched controls. The relationship between body composition and blood Phe was analyzed within the PKU cohort from clinically collected dried blood spot Phe concentrations.

Results

Male subjects with PKU had less LBM% and more FM% than controls (p = .024). There was no difference in LBM% and FM% among female subjects. Age (p = .02) and FM% (p = .02) were positively correlated to dried blood spot Phe. Synthetic protein intake (g/kg body weight) was negatively correlated with dried blood spot Phe (p = .04). Natural protein intake was not related to blood spot Phe.

Conclusions

Children with PKU face additional dietary challenges maintaining healthy growth and body composition while keeping Phe levels low. We observed higher FM% and lower LBM% in male subjects with PKU. Correlations do not prove cause and effect but suggest a relationship between increased blood Phe, lower synthetic protein intake and increased FM%. Future studies may explore if lower blood Phe concentrations is associated with a lower FM% and higher LBM%; particularly among adult patients now managed on pegvaliase (Palynziq®) who consume normal amounts of natural protein or among younger patients who consume glycomacropeptide (GMP).

Nutritional and metabolic parameters of children and adolescents with phenylketonuria

BACKGROUND AND AIMS

Considering that phenylalanine-poor diets may be monotonous and compromise the development and nutritional status of children and adolescents with phenylketonuria, the aim of this study was to evaluate the anthropometric and biochemical characteristics of children and adolescents with this condition.

METHODS

Retrospective study with anthropometric and biochemical data collection from patients with phenylketonuria in the age group 2-19.9 years. Nutritional status was classified according to the World Health Organization. Biochemical tests were compared to current recommendations.

RESULTS

A total of 84 patients (71.8%) were eligible, with a median age of 10.7 years (2.4-19.9 years). There was predominance of adequate (n = 58, 69%) with presence of overweight and obesity in 24 (28.5%) patients. The biochemical tests revealed hyperphosphatemia in 46 (55%), hypertriglyceridemia in 27 (50%), vitamin B12 elevated in 34 (41.2%), selenium deficiency in 10 (13.7%), insufficient zinc in 7 (8.9%), low globulin in 21 (26.9%), low HDL in 35 (59.3%) and elevated phenylalanine level in 28 (34.5%) patients in the sample. Overweight and obesity were correlated with low HDL (p = 0.04) and lowest adequate frequency of LDL (p = 0.09). Higher phosphorus values were associated with lower body weight (r = -0.72) and age (r = -0.75), as well as vitamin B12 in the same parameters (r = -0.67 and r = -0, 68). A positive correlation of phenylalanine with body weight and age (r = 0.62 and r = 0.66) was observed.

CONCLUSION

Most patients presented adequate according to anthropometric parameters and appropriate biochemical tests, except HDL, and moderate metabolic control of the disease. However, attention should be paid to the presence of overweight and need for biochemical monitoring of triglycerides, selenium, zinc, HDL, and phenylalanine.

OVERWEIGHT AND ASSOCIATED FACTORS IN CHILDREN AND ADOLESCENTS WITH PHENYLKETONURIA: A SYSTEMATIC REVIEW

Objective:

To verify the occurrence of overweight in children and adolescents with phenylketonuria and to identify possible causal factors.

Data sources:

A systematic review was performed in the SciELO, PubMed and VHL databases using the descriptors “Phenylketonurias”, “Overweight”, “Child” and “Adolescent”. Original articles conducted with children and adolescents, published between 2008 and 2018 in Portuguese, English or Spanish languages were included.

Data synthesis:

A total of 16 articles were identified and, after screening procedures, 6 studies were selected for the review. Overweight in children and adolescents with phenylketonuria was a frequent occurence in the studies included in this review, ranging from 7.8 to 32.6%. The female sex was the most affected by the nutritional disorder. Furthermore, a high caloric intake combined with a lack of stimuli to practice physical activities were main factors associated with the excessive weight in the population of interest.

Conclusions:

Excess weight can be considered a common outcome in children and adolescents with phenylketonuria. It is mainly caused by inadequate food consumption and sedentary lifestyle. The importance of early identification of nutritional disturbances in children and adolescents with phenylketonuria should be emphasized, in order to prevent associated chronic diseases and to promote health by encouraging continued healthy eating habits and the regular practice of physical exercises.

Phenylketonuria, co-morbidity, and ageing: A review

Phenylketonuria (PKU) is a metabolic condition which, left untreated, results in severe and irreversible brain damage. Newborn screening and the development of the low phenylalanine (Phe) diet have transformed the outcomes for people with PKU. Those who have benefited from early treatment are now approaching their fifth and sixth decade. It is therefore timely to consider multi-morbidity in PKU and the effects of ageing, in parallel with the wider benefits of emerging treatment options in addition to dietary relaxation. We have conducted the first literature review of co-morbidity and ageing in the context of PKU. Avenues explored have emerged from limited study of multi-morbidity to date and the knowledge and critical enquiry of the authors. Findings suggest PKU to have a wider impact than brain development, and result in several intriguing questions that require investigation to attain the best outcomes for people with PKU in adulthood moving through to older age. We recognise the difficulty in studying longitudinal outcomes in rare diseases and emphasise the necessity to develop PKU registries and cohorts that facilitate well-designed studies to answer some of the questions raised in this review. Whilst awaiting new information in these areas we propose that clinicians engage with patients to make personalised and well-informed decisions around Phe control and assessment for co-morbidity.

Nutritional and Metabolic Characteristics of UK Adult Phenylketonuria Patients with Varying Dietary Adherence

The nutritional and metabolic characteristics of adult phenylketonuria (PKU) patients in the UK with varying dietary adherence is unknown. In other countries, nutritional and metabolic abnormalities have been reported in nonadherent patients compared to adherent counterparts. A pooled analysis of primary baseline data from two UK multi-centre studies was therefore performed to establish whether this is true from a UK perspective. Adult PKU patients who had provided 3-day food records and amino acid blood samples were included and grouped according to dietary adherence (adherent; n = 16 vs. nonadherent; n = 14). Nonadherent patients consumed greater amounts of natural protein compared to adherent patients (61.6 ± 30.7 vs. 18.3 ± 7.7 g/day; q < 0.001). In contrast, the contribution of protein substitutes to total protein intake was lower in nonadherent compared to adherent patients (3.9 ± 9.2 g/day vs. 58.6 ± 10.2 g/day; q < 0.001). Intakes of iron, zinc, vitamin D₃, magnesium, calcium, selenium, iodine, vitamin C, vitamin A and copper were significantly lower in nonadherent compared to adherent patients and were below UK Reference Nutrient Intakes. Similarly, intakes of thiamin, riboflavin, niacin, vitamin B₆ and phosphorus were significantly lower in nonadherent compared to adherent patients but met the UK Reference Nutrient Intakes. Phenylalanine concentrations in nonadherent patients were significantly higher than adherent patients (861 ± 348 vs. 464 ± 196 µmol/L; q=0.040) and fell outside of European treatment target ranges. This study shows the nutritional and metabolic consequences of deviation from phenylalanine restriction and intake of PKU protein substitutes in nonadherent adult PKU patients. Collectively, these data further underlie the importance of life-long adherence to the PKU diet.

The cardiovascular phenotype of adult patients with phenylketonuria

BACKGROUND

Patients with Phenylketonuria (PKU) are exposed to multiple cardiovascular risk factors, but the clinical significance of these abnormalities is yet unknown. The purpose of this study was to characterize the cardiovascular phenotype in adult patients with PKU by clinical and dietary data, measurements of biochemical markers, and non-invasive examination of vascular functions.

RESULTS

Twenty-three adult patients with PKU (age: 18-47 y; 30.8 ± 8.4 y) and 28 healthy controls (age: 18-47 y; 30.1 ± 9.1 y) were included in this study. PKU patients had significantly higher systolic and diastolic blood pressure, increased resting heart rate and a higher body mass index. Total cholesterol and non-HDL cholesterol levels were significantly increased in PKU patients, whereas plasma levels of HDL cholesterol and its subfraction HDL2 (but not HDL3) were significantly decreased. The inflammatory markers C-reactive protein and serum amyloid A protein and the serum oxidative stress marker malondialdehyde were significantly higher in patients with PKU. Venous occlusion plethysmography showed marked reduction in post-ischemic blood flow and the carotid to femoral pulse wave velocity was significantly increased demonstrating endothelial dysfunction and increased vascular stiffness.

CONCLUSIONS

This study shows that the cardiovascular phenotype of adult PKU patients is characterized by an accumulation of traditional cardiovascular risk factors, high levels of inflammatory and oxidative stress markers, endothelial dysfunction and vascular stiffness. These data indicate the need for early cardiovascular risk reduction in patients with PKU.

Long-Term Growth in Phenylketonuria: A Systematic Review and Meta-Analysis

There is an ongoing debate regarding the impact of phenylketonuria (PKU) and its treatment on growth. To date, evidence from studies is inconsistent, and data on the whole developmental period is limited. The primary aim of this systematic review was to investigate the effects of a phenylalanine (Phe)-restricted diet on long-term growth in patients with PKU. Four electronic databases were searched for articles published until September 2018. A total of 887 results were found, but only 13 articles met eligibility criteria. Only three studies had an adequate methodology for meta-analysis. Although the results indicate normal growth at birth and during infancy, children with PKU were significantly shorter and had lower weight for age than reference populations during the first four years of life. Impaired linear growth was observed until the end of adolescence in PKU. In contrast, growth impairment was not reported in patients with mild hyperphenylalaninemia, not requiring dietary restriction. Current evidence indicates that even with advances in dietary treatments, “optimal” growth outcomes are not attained in PKU. The majority of studies include children born before 1990s, so further research is needed to show the effects of recent dietary practices on growth in PKU.

Overweight in classical phenylketonuria children: A retrospective cohort study

PURPOSE

This cohort study aimed to determine the frequency of overweight and obesity in classical phenylketonuria children and to identify the possible influence of metabolic control on the BMI of the studied patients.

PATIENTS AND METHODS

The study group included 63 classical phenylketonuria patients (40 girls and 23 boys; aged 5-16 years). Their z-score BMI, metabolic control, educational level of parents and socioeconomic status were determined.

RESULTS

Twenty children were overweight or obese and only three were underweight. The percentages of overweight and obese children were 31.7% for the whole group, 21.7% (5 out of 23) for boys and 37.5% (15 out of 40) for girls. Overweight and obesity in these phenylketonuria patients was statistically significantly more frequent when compared to national reference studies (p = 0.0031). The five-year index of dietary control and the percentage of spikes exceeding 6 and 12 mg/dl (Spikes 6 and 12) indicated better metabolic control in the case of normal weight children than those who were overweight and obese (p < 0.049, p < 0.041 and p < 0.011, respectively). The odds ratio of being overweight or obese for those having poorer metabolic control (values higher vs lower than mean) was statistically significantly higher than for the remaining patients (for Spikes 12: 6.926 < 95%CI: 2.011-23.854 > ; p < 0.002). These results strongly suggest a link between overweight and diet non-compliance.

CONCLUSIONS

Children with classical phenylketonuria presented higher odds of being overweight or obese as compared with reference national studies, with girls only having a higher frequency of overweight.

Asymmetric dimethylarginine as a potential biomarker for management and follow-up of phenylketonuria

Phenylketonuria's (PKU) treatment based on low-protein diet may affect other metabolic pathways, such as that of asymmetric dimethylarginine (ADMA). The aim of this study was to evaluate the reliability of ADMA as a biomarker of adequate metabolic control and possible nutritional risk in a long-term PKU patient population. One hundred and six dietary-treated PKU patients from four hospitals in Spain were enrolled in this cross-sectional study. Their lipid profile, total homocysteine, ADMA, and symmetric dimethylarginine (SDMA) concentrations were analyzed and compared with a control group. Sensitivity, specificity, and likelihood ratios of the proposed biomarker were calculated. PKU patients had statistically significant lower plasmatic ADMA, SDMA, and arginine concentrations as compared with the control group (p < 0.001). Significant correlations were found between ADMA, phenylalanine, and total homocysteine levels. The ADMA/creatinine ratio correlated with phenylalanine levels as metabolic control and nutritional risk in PKU patients. Its reliability as a management biomarker was studied with positive results. The ADMA/creatinine ratio might serve as an independent biomarker in the management of PKU patients, different from blood phenylalanine levels. It could be of particular usefulness to detect those who are following an unbalanced diet that could have long-term negative effects.Conclusion: In this study, we have evaluated the reliability of ADMA as a potential biomarker of adequate metabolic control and possible nutritional risk in a long-term PKU patient population. What is Known: • Although PKU individuals have lower values of ADMA even with blood Phe levels in the recommended range, little attention is payed to other metabolic pathways. What is New: • ADMA could be used as new biomarker for PKU management and follow-up of the diet, after evaluating their reliability in a long-term PKU patient population.

Acute effect of an amino acid mixture in the rat glycemic profile

Amino acid mixtures (AAM) are protein substitutes used for phenylketonuria treatment, but their metabolic effects have not been well characterized. The objective of this study was to compare the acute glycemic response to free amino acids (free AA) from AAM with the response to intact protein (iProtein). Male Wistar rats (n = 14) were administered by gavage a bolus of free AA (n = 7) or iProtein as albumin (n = 7) containing equivalent amounts of nitrogen. Blood glucose and insulin levels were measured at baseline and 15, 30, 60 and 120 minutes later, when gut GLP-1 content and pancreatic insulin, GLP-1 receptor and Ki67 expression were quantified at 120 minutes time point. After AAM, glucose area under the curve (free AA vs iProtein; P < 0.01), serum insulin levels at 120 minutes (free AA vs iProtein; P < 0.05), colon GLP-1 content (free AA vs iProtein; P < 0.01), pancreatic GLP-1 receptor (free AA vs iProtein; P < 0.01) and insulin expression (free AA vs iProtein; p < 0.01) were significantly lower as compared with iProtein. AAM increased Ki67 expression in pancreatic islets (free AA vs iProtein; P < 0.05). In conclusion, this study demonstrated that acute response to AAM differs from iProtein and is characterized by a lower glucose excursion, along with a decrease in gut GLP-1 and pancreatic GLP-1 receptor and insulin. This data suggests the modulation of glycemia by free AA is mediated by the incretin axis.

Severe acute pancreatitis in a child with phenylketonuria

We report for the first time severe acute pancreatitis in a child treated for phenylketonuria (PKU) discovered on neonatal screening. This 2-year-old boy was first hospitalized for bilious vomiting and moderate back pain. Laboratory values included a lipase level of 1.142 U/L, a phenylalanine level of 10mg/dL, and computed tomography revealed Balthazar grade E pancreatitis. Continuous enteral feeding was started on the 3rd day after admission. We observed clinical and biological improvement. Etiologic investigations for pancreatitis returned negative. Despite the severity of the pancreatitis, we did not observe decompensation of the metabolic disease. Specific nutritional management was necessary.

Carbohydrate status in patients with phenylketonuria

BACKGROUND

In patients with phenylketonuria (PKU), a low-phenylalanine (Phe) diet supplemented with low-protein foods and a Phe-free amino acid mixture favors a dietary intake rich in carbohydrates, but little is known about how these molecules are metabolized in this setting. The objective of the present study was to analyze carbohydrate metabolism in patients with hyperphenylalaninemia.

METHODS

We conducted a multicenter cross-sectional study to investigate biochemical markers of basal and postprandial carbohydrate metabolism in PKU patients according to age, Phe tolerance, waist circumference and body mass index (BMI), diet, tetrahydrobiopterin (BH4) supplementation, and adherence to treatment. Basal biomarkers and anthropometric parameters were also evaluated in patients with mild hyperphenylalaninemia (MHPA) and in healthy controls.

RESULTS

A total of 83 patients aged 4-52 years were studied; 68.7% had PKU and 31.3% had MHPA. 68 healthy controls of similar sex and age were also evaluated Metabolic control was adequate in 71.9% of PKU patients. Fasting glucose levels (mean 80.77 ± 8.06 mg/dL) were high in just one patient, but fasting insulin levels, with a mean of 12.74 ± 8.4 mIU/L, were altered in 15 PKU patients (26.3%) and markedly higher than in patients with MPHA (p = 0.035). Fasting insulin levels and Homeostasis Model Assessment Insulin Resistance (HOMA-IR) were significantly higher than in healthy controls and correlated with body mass index, waist circumference, age, and also showed statistically significant differences according to diagnosis and Phe tolerance (p < 0.05). Patients under BH4 therapy had lower insulin levels and HOMA-IR. A higher mean carbohydrate intake from AA mixtures was observed in classic PKU patients. The caloric intake in the form of carbohydrates was also higher in PKU than MHPA patients (p = 0.038) and it was correlated with basal insulin (rho = 0.468, p = 0.006), HOMA-IR (rho = 0.423, p = 0.02), BMI (rho 0.533, p = 0.002), and waist circumference (rho 0.584, p = 0.0007).

CONCLUSIONS

This study shows that PKU patients are at risk of carbohydrate intolerance and insulin resistance, more evident in adults and overweight patients, probably related to their higher caloric intake in form carbohydrate content. A higher dependency of AA mixtures was demonstrated in PKU patients.

Status of nutrients important in brain function in phenylketonuria: a systematic review and meta-analysis

Background

Despite early and ongoing dietary management with a phe-restricted diet, suboptimal neuropsychological function has been observed in PKU. The restrictive nature of the PKU diet may expose patients to sub-optimal nutritional intake and deficiencies which may impact normal brain function. A systematic review of the published literature was carried out, where possible with meta-analysis, to compare the status of nutrients (Nutrients: DHA, EPA phospholipids, selenium, vitamins B₆, B₁₂, E, C, A, D, folic acid, choline, uridine, calcium, magnesium, zinc, iron, iodine and cholesterol) known to be important for brain development and functioning between individuals with PKU and healthy controls.

Results

Of 1534 publications identified, 65 studies met the entry criteria. Significantly lower levels of DHA, EPA and cholesterol were found for PKU patients compared to healthy controls. No significant differences in zinc, vitamins B₁₂, E and D, calcium, iron and magnesium were found between PKU patients and controls. Because of considerable heterogeneity, the meta-analyses findings for folate and selenium were not reported. Due to an insufficient number of publications (< 4) no meta-analysis was undertaken for vitamins A, C and B₆, choline, uridine, iodine and phospholipids.

Conclusions

The current data show that PKU patients have lower availability of DHA, EPA and cholesterol. Compliance with the phe-restricted diet including the micronutrient fortified protein substitute (PS) is essential to ensure adequate micronutrient status. Given the complexity of the diet, patients’ micronutrient and fatty acid status should be continuously monitored, with a particular focus on patients who are non-compliant or poorly compliant with their PS. Given their key role in brain function, assessment of the status of nutrients where limited data was found (e.g. choline, iodine) should be undertaken. Standardised reporting of studies in PKU would strengthen the output of meta-analysis and so better inform best practice for this rare condition.

Electronic supplementary material

The online version of this article (10.1186/s13023-018-0839-x) contains supplementary material, which is available to authorized users.

The influence of parental food preference and neophobia on children with phenylketonuria (PKU)

Background

In a previous case-control study, we demonstrated that children with PKU and non-PKU controls preferred sweet foods. Additionally, children with PKU exhibited food neophobia, with no preference for bitter tasting foods associated with the taste of phenylalanine (Phe)-free L-amino acid supplements.

Objective

In an observational extension study, we evaluated the influence of parental food choice and neophobia on their children's taste preferences and food neophobia.

Methods

Male and female parents/caregivers of 35 children with PKU and 35 control parents, completed a neophobia and food frequency questionnaire for comparison using the same questionnaires that they completed for their children.

Results

Both groups of children (PKU and non PKU control) were rated as more food neophobic and exhibited more neophobic behaviour than parents, although children with PKU more so than non-PKU controls (PKU food neophobia p < 0.0001vs control 0.001; PKU general neophobia p = 0.003 vs control p = 0.04). Both groups of children ate significantly more sweets, sweetened drinks and potato fries than their parents but differences were greater for children with PKU who also consumed more high carbohydrate (low protein) staple foods such as bread and pasta, and more sweet snacks such as biscuits than their parents. Non-PKU control children's food choices were closer to their parent's choices.

Conclusions

In PKU, parental food choices and their food neophobia have limited influence on their children's eating habits. Food neophobia in children with PKU may be associated with fear of eating unfamiliar foods potentially containing a source of protein or aspartame. Their preference for sweet foods may be influenced by limited food choices and habitual consumption of artificially sweetened L-amino acid supplements.

The complete European guidelines on phenylketonuria: diagnosis and treatment

Phenylketonuria (PKU) is an autosomal recessive inborn error of phenylalanine metabolism caused by deficiency in the enzyme phenylalanine hydroxylase that converts phenylalanine into tyrosine. If left untreated, PKU results in increased phenylalanine concentrations in blood and brain, which cause severe intellectual disability, epilepsy and behavioural problems. PKU management differs widely across Europe and therefore these guidelines have been developed aiming to optimize and standardize PKU care. Professionals from 10 different European countries developed the guidelines according to the AGREE (Appraisal of Guidelines for Research and Evaluation) method. Literature search, critical appraisal and evidence grading were conducted according to the SIGN (Scottish Intercollegiate Guidelines Network) method. The Delphi-method was used when there was no or little evidence available. External consultants reviewed the guidelines. Using these methods 70 statements were formulated based on the highest quality evidence available. The level of evidence of most recommendations is C or D. Although study designs and patient numbers are sub-optimal, many statements are convincing, important and relevant. In addition, knowledge gaps are identified which require further research in order to direct better care for the future.

The relationship between dietary intake, growth and body composition in Phenylketonuria

AIM

Phenylketonuria (PKU) is an inborn error of protein metabolism that results from perturbation in phenylalanine hydroxylase activity leading to elevated blood levels of phenylalanine (phe). We aimed to explore the relationships between dietary patterns (total-protein, natural-protein, amino-acid formula), and the ratio of protein to energy intake with growth and body composition.

METHOD

Longitudinal prospective data (1-6 measurements) of growth, dietary intake and body composition in patients treated with phe-restricted diet only (D-PKU; n=32), and tetrahydrobiopterin (BH₄)±phe-restricted diet (BH₄-PKU; n=5) were collected over a two-year period. Healthy siblings provided control data (n=21).

RESULTS

There were no significant differences in weight-, height-, BMI z-score or percent body fat mass (%fatmass) between the D-PKU, BH₄-PKU and control groups or between the all-types of PKU combined and controls, which confirmed 'normal' growth in the PKU cohort. Total-protein intake in the all-types of PKU group met or exceeded WHO safe protein recommendations. There were no significant relationships between anthropometric and dietary variables. Significant negative correlations were found in body composition: %fatmass and total-protein intake (r_s=-0.690, p≤0.001), natural-protein intake (r_s=-0.534, p=0.001), and AAF intake (r_s=-0.510, p=0.001). Age was significantly correlated with %fatmass (r_s=0.493, p=0.002) A total-protein intake of 1.5-2.6g/kg/day and natural-protein intake >0.5g/kg/day were associated with improved body composition. An apparent safe P:E ratio of 3.0-4.5g protein/100kcal was strongly associated with appropriate growth outcomes.

CONCLUSIONS

Clinical decision-making needs to consider both the enhancement of natural-protein tolerance and the application of an apparent 'safe' protein to energy ratio to support optimal growth and body composition in PKU.

Protein intake and physical activity are associated with body composition in individuals with phenylalanine hydroxylase deficiency

OBJECTIVE

Determine whether body composition as it relates to dietary protein in patients with phenylalanine hydroxylase (PAH) deficiency is associated with genotype, dietary factors, and lifestyle choices.

METHODS

We examined associations between protein intake (intact and medical foods: MF) and body composition in PAH-deficient patients along with, physical activity, and genotype. Protein intakes (total, intact, and MF) were analysed from three-day food records with Nutrition Data System for Research (NDSR) in 59 children and 27 adults (N=86, median age=16.0years). The severity of PAH deficiency was classified using the genotype assigned value method (AV sum). Physical activity was assessed using a study-developed question (light vs. intense activity). Body composition was measured by DXA, including android:gynoid ratio (A:G), fat-free mass index (FFMI), fat mass index (FMI), and FMI:FFMI ratio.

RESULTS

High intact protein intake was associated with high FFMI (r_s=0.75, p=0.008) and low FMI:FFMI (r_s=-0.59, p=0.04) in adults. Only in children, MF protein (r_s=0.38, p=0.04) was directly proportional to FFMI. Median intact protein intakes of adults (25.1 vs. 9.9g/d, p<0.001) and children (11 vs. 6g/d, p<0.001) were higher than prescribed. Only in adults, the actual median MF protein intake was lower than prescribed (53 vs. 60g/d, p=0.03). In adults and children, light activity was associated with higher fat mass indices compared to intense activity (adults: FMI:FFMI: β=1.1, p=0.001, children: FMI:FFMI: β=1.1, p=0.007; FMI β=2.1, p=0.01; A:G β=1.1, p=0.04). All associations remained significant after covariate adjustment. Genotype was not associated with body composition.

CONCLUSIONS

Although fat-free mass in adults was positively associated with intact protein intake, it should be consumed as prescribed per individual tolerance to maintain plasma Phe concentrations within treatment range. In children, total protein maximized with MF should be encouraged to promote lean mass. Nutrition counselling could be complemented with physical activity recommendations for optimal clinical outcomes.

Nutritional status in patients with phenylketonuria using glycomacropeptide as their major protein source

BACKGROUND/OBJECTIVES

Low phenylalanine (PHE), glycomacropeptide-based protein substitute (GMP) is an alternative to traditional L-amino acid supplements (AA) used in the dietary management of phenylketonuria (PKU). In a retrospective, longitudinal study, we report the nutritional status of PKU patients taking AA and GMP.

SUBJECTS/METHODS

Eleven PKU patients aged 27±10 years (1 HPA, 4 mild and 6 classical PKU) on dietary treatment were evaluated (anthropometry, body composition, blood pressure measurements, biochemical markers including vitamin, mineral, lipids, carbohydrates and protein status/metabolism, and nutritional intake assessment) at two different annual reviews. The mean time taking AA was 13±5 months and GMP 13±7 months. Blood phenylalanine (PHE) and tyrosine (TYR) were analysed before and after GMP introduction.

RESULTS

Both GMP and AA protein substitutes provided similar protein equivalent intake (0.85 vs 0.75 g/kg/day, P=0.182). In the GMP group, it contributed 57% (27-100%) of the protein substitute intake (with AA delivering the rest of protein substitute intake), providing an additional 34±12 mg/day PHE. Nutritional intake, anthropometry and body composition measurements were similar in both the groups. Median blood PHE did not change (P=0.594), although values within target range improved (36 vs 46%), but this was not statistically significant. Mean blood TYR increased (52.0±19.2 vs 63.2±25.6 μmol/l, P=0.033), and all biochemical markers remained stable, except for a lower A1C haemoglobin (P=0.011).

CONCLUSIONS

Partial GMP contribution to total protein substitute intake did not affect nutritional status in patients with PKU. Blood PHE control was not adversely affected. The increased blood TYR after GMP introduction necessitates further study.

Hyperphenylalaninemia Correlated with Global Decrease of Antioxidant Genes Expression in White Blood Cells of Adult Patients with Phenylketonuria

BACKGROUND

Several studies have highlighted disturbance of redox homeostasis in patients with phenylketonuria (PKU) which may be associated with neurological disorders observed in patients, especially during adulthood when phenylalanine restrictive diets are not maintained. The aim of this study was to assess the antioxidant profile in a cohort of PKU patients in comparison to the controls and to evaluate its relation to biochemical parameters especially phenylalaninemia.

METHODS

We measured RNA expression of 22 antioxidant genes and reactive oxygen species (ROS) levels in white blood cells of 10 PKU patients and 10 age- and gender-matched controls. We also assessed plasma amino acids, vitamins, oligo-elements, and urinary organic acids concentrations. Then we evaluated the relationship between redox status and biochemical parameters.

RESULTS

In addition to expected biochemical disturbances, we highlighted a significant global decrease of antioxidant genes expression in PKU patients in comparison to the controls. This global decrease of antioxidant genes expression, including various isoforms of peroxiredoxins, glutaredoxins, glutathione peroxidases, and superoxide dismutases, was significantly correlated to hyperphenylalaninemia.

CONCLUSION

This study is the first to evaluate the expression of 22 antioxidant genes in white blood cells regarding biochemical parameters in PKU. These findings highlight the association of hyperphenylalaninemia with antioxidant genes expression. New experiments to specify the role of oxidative stress in PKU pathogenesis may be useful in suggesting new recommendations in PKU management and new therapeutic trials based on antioxidant defenses.

Dietary glycemic index, glycemic load and metabolic profile in children with phenylketonuria

BACKGROUND AND AIMS

No data exist in the current literature on the glycemic index (GI) and glycemic load (GL) of the diet of phenylketonuric (PKU) children. The aims of this study were to examine the dietary GI and GL in PKU children on a low-phenylalanine (Phe)-diet and to evaluate whether an association may exist between the carbohydrate quality and the metabolic profile.

METHODS

Twenty-one PKU children (age 5-11 years) and 21 healthy children, gender and age matched, were enrolled. Dietary (including GI and GL) and blood biochemical assessments were performed.

RESULTS

No difference was observed for daily energy intake between PKU and healthy children. Compared to healthy controls, PKU children consumed less protein (p = 0.001) and fat (p = 0.028), and more carbohydrate (% of total energy, p = 0.004) and fiber (p = 0.009). PKU children had higher daily GI than healthy children (mean difference (95% confidence interval), 13.7 (9.3-18.3)) and higher GL (31.7 (10.1-53.2)). PKU children exhibited lower blood total and low density lipoprotein cholesterol (LDL) levels (p < 0.01) and higher triglyceride level (p = 0.014) than healthy children, while glucose and insulin concentrations did not differ. In PKU children the dietary GL was associated with triglyceride glucose index (Spearman's correlation coefficient = 0.515, p = 0.034).

CONCLUSION

In PKU children a relationship of the dietary treatment with GI and GL, blood triglycerides and triglyceride glucose index may exist. Improvement towards an optimal diet for PKU children could include additional attention to the management of dietary carbohydrate quality.

The Indicator Amino Acid Oxidation Method with the Use of l-[1-13C]Leucine Suggests a Higher than Currently Recommended Protein Requirement in Children with Phenylketonuria

BACKGROUND

Phenylketonuria is characterized by mutations in the Phe hydroxylase gene that leads to the accumulation of Phe in plasma and the brain. The standard of care for phenylketonuria is nutritional management with dietary restriction of Phe and the provision of sufficient protein and energy for growth and health maintenance. The protein requirement in children with phenylketonuria is empirically determined based upon phenylketonuria nutritional guidelines that are adjusted individually in response to biochemical markers and growth.

OBJECTIVE

We determined dietary protein requirements in children with phenylketonuria with the use of the indicator amino acid oxidation (IAAO) technique, with l-[1-¹³C]Leu as the indicator amino acid.

METHODS

Four children (2 males; 2 females) aged 9-18 y with phenylketonuria [mild hyperphenylalanemia (mHPA); 6-10 mg/dL (360-600 μmol/L)] were recruited to participate in ≥7 separate test protein intakes (range: 0.2-3.2 g ⋅ kg^-1 ⋅ d^-1) with the IAAO protocol with the use of l-[1-¹³C]Leu followed by the collection of breath and urine samples over 8 h. The diets were isocaloric and provided energy at 1.7 times the resting energy expenditure. Protein was provided as a crystalline amino acid mixture based on an egg protein pattern, except Phe and Leu, which were maintained at a constant across intakes. Protein requirement was determined with the use of a 2-phase linear-regression crossover analysis of the rate of l-[1-¹³C]Leu tracer oxidation.

RESULTS

The mean protein requirement was determined to be 1.85 g ⋅ kg^-1 ⋅ d^-1 (R² = 0.66; 95% CI: 1.37, 2.33). This result is substantially higher than the 2014 phenylketonuria recommendations (1.14-1.33 g ⋅ kg^-1 ⋅ d^-1; based on 120-140% above the current RDA for age).

CONCLUSIONS

To our knowledge, this is the first study to directly define a quantitative requirement for protein intake in children with mHPA and indicates that current protein recommendations in children with phenylketonuria may be insufficient. This trial was registered at clinicaltrials.gov as NCT01965691.

Dietary intervention in the management of phenylketonuria: current perspectives

Phenylketonuria (PKU) is a well-described inborn error of amino acid metabolism that has been treated for >60 years. Enzyme deficiency causes accumulation of phenylalanine (Phe) and if left untreated will lead to profound and irreversible intellectual disability in most children. Traditionally, it has been managed with a low-Phe diet supplemented with a Phe-free protein substitute although newer treatment options mainly in combination with diet are available for some subgroups of patients with PKU, for example, sapropterin, large neutral amino acids, and glycomacropeptide. The diet consists of three parts: 1) severe restriction of dietary Phe; 2) replacement of non-Phe l-amino acids with a protein substitute commonly supplemented with essential fatty acids and other micronutrients; and 3) low-protein foods from fruits, some vegetables, sugars, fats and oil, and special low-protein foods (SLPF). The prescription of diet is challenging for health professionals. The high-carbohydrate diet supplied by a limited range of foods may program food preferences and contribute to obesity in later life. Abnormal tasting and satiety-promoting protein substitutes are administered to coincide with peak appetite times to ensure their consumption, but this practice may impede appetite for other important foods. Intermittent dosing of micronutrients when combined with l-amino acid supplements may lead to their poor bioavailability. Much work is required on the ideal nutritional profiling for special SLPF and Phe-free l-amino acid supplements. Although non-diet treatments are being studied, it is important to continue to fully understand all the consequences of diet therapy as it is likely to remain the foundation of therapy for many years.

Lipid profile status and other related factors in patients with Hyperphenylalaninaemia

BACKGROUND

The mainstay of treating patients with phenylketonuria (PKU) is based on a Phe-restricted diet, restrictive in natural protein combined with Phe-free L-amino acid supplements and low protein foods. This PKU diet seems to reduce atherogenesis and confer protection against cardiovascular diseases but the results from the few published studies have been inconclusive. The aim of our study was to evaluate the relationship between the lipid profile and several treatment-related risk factors in patients with hyperphenylalaninaemia (HPA) in order to optimize their monitoring.

METHODS

We conducted a cross-sectional multicentre study. A total of 141 patients with HPA were classified according to age, phenotype, type of treatment and dietary adherence. Annual median blood phenylalanine (Phe) levels, Phe tolerance, anthropometric measurements, blood pressure (BP) and biochemical parameters [(triglycerides, total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low density lipoprotein-cholesterol (LDL-C), apolipoprotein A (ApoA), apolipoprotein B (ApoB), vitamin B12, total homocysteine (tHcy), Methionine (Met), high sensitivity C-Reactive Protein (hsCRP)] were collected for each patient.

RESULTS

Plasma TC levels were lower in patients with PKU than in the mild-HPA group (150 ± 31 vs. 164 ± 22 mg/dL), and there was a weak inverse correlation between plasma TC and Phe levels. HDL-C, LDL-C, ApoA and ApoB levels were lower in the PKU group than in mild-HPA. Patients with PKU had higher systolic BP than the mild-HPA group and there was found a quadratic correlation between median Phe levels and systolic BP (p = 6.42e(-5)) and a linear correlation between median Phe levels and diastolic BP (p = 5.65e(-4)). In overweight or obese PKU patients (24.11 %), biochemical parameters such as TC, triglycerides, LDL-C, tHcy, hsCRP and BP were higher. By contrast, HDL-C was lower in these patients.

CONCLUSION

Our data show a direct correlation between lipid profile parameters and good adherence to the diet in PKU patients. However, lipid profile in overweight or obese patients displayed an atherogenic profile, in addition to higher hsCRP concentrations and BP. Our study contributes to a better understanding of the relationship between phenotype and treatment in patients with HPA, which could be useful in improving follow-up strategies and clinical outcome.

TRIAL REGISTRATION

Research Ethics Committee of Santiago-Lugo 2015/393. Registered 22 September 2015, retrospectively registered.

Updated, web-based nutrition management guideline for PKU: An evidence and consensus based approach

BACKGROUND

In 2014, recommendations for the nutrition management of phenylalanine hydroxylase deficiency were published as a companion to the concurrently published American College of Medical Genetics and Genomics guideline for the medical treatment of phenylketonuria (PKU). These were developed primarily from a summary of findings from the PKU scientific review conference sponsored by the National Institutes of Health and Agency for Healthcare Research & Quality along with additional systematic literature review. Since that time, the Genetic Metabolic Dietitians International and the Southeast Regional Newborn Screening and Genetics Collaborative have partnered to create a web-based technology platform for the update and development of nutrition management guidelines for inherited metabolic disorders.

OBJECTIVE

The purpose of this PKU guideline is to establish harmonization in treatment and monitoring, to guide the integration of nutrition therapy in the medical management of PKU, and to improve outcomes (nutritional, cognitive, and developmental) for individuals with PKU in all life stages while reducing associated medical, educational, and social costs.

METHODS

Six research questions critical to PKU nutrition management were formulated to support guideline development: Review, critical appraisal, and abstraction of peer-reviewed studies and unpublished practice literature, along with expert Delphi survey feedback, nominal group process, and external review from metabolic physicians and dietitians were utilized for development of recommendations relevant to each question. Recommendations address nutrient intake, including updated protein requirements, optimal blood phenylalanine concentrations, nutrition interventions, monitoring parameters specific to life stages, adjunct therapies, and pregnancy and lactation. Recommendations were graded using a rigorous system derived from the Academy of Nutrition and Dietetics.

RESULTS AND CONCLUSION

These guidelines, updated utilizing a thorough and systematic approach to literature analysis and national consensus process, are now easily accessible to the global community via the newly developed digital platform. For additional details on specific topics, readers are encouraged to review materials on the online portal: https://GMDI.org/.

Comparison of atherogenic risk factors among poorly controlled and well-controlled adolescent phenylketonuria patients

BACKGROUND

Previous studies investigating the known risk factors of atherosclerosis in phenylketonuria patients have shown conflicting results. The primary aim of our study was to investigate the serum atherogenic markers in adolescent classical phenylketonuria patients and compare these parameters with healthy peers. The secondary aim was to compare these atherogenic markers in well-controlled and poorly controlled patients.

METHODS

A total of 59 patients (median age: 12.6 years, range: 11-17 years) and 44 healthy controls (median age: 12.0 years, range: 11-15 years) were enrolled in our study. Phenylketonuria patients were divided into two groups: well-controlled (serum phenylalanine levels below 360 µmol/L; 24 patients) and poorly controlled patients (serum phenylalanine levels higher than 360 µmol/L).

RESULTS

The mean high-density lipoprotein cholesterol levels of well-controlled patients (1.0±0.2 mmol/L) were significantly lower compared with poorly controlled patients and controls (1.1±0.2 mmol/L, p=0.011 and 1.4±0.2 mmol/L, p<0.001, respectively). Poorly controlled patients had lower high-density lipoprotein cholesterol levels than healthy controls (p=0.003). Homocysteine levels of both well-controlled (9.8±6.4 µmol/L) and poorly controlled (9.2±5.6 µmol/L) patients were higher compared with controls (5.8±1.8 µmol/L, p<0.01). The mean platelet volume of well-controlled patients (9.5±1.1 fL) was higher than that of poorly controlled patients and controls (8.9±0.8 fL, p=0.024 and 7.7±0.6 fL, p<0.001, respectively).

CONCLUSION

Lower high-density lipoprotein cholesterol and higher homocysteine and mean platelet volume levels were detected in phenylketonuria patients. In particular, these changes were more prominent in well-controlled patients. We conclude that phenylketonuria patients might be at risk for atherosclerosis, and therefore screening for atherosclerotic risk factors should be included in the phenylketonuria therapy and follow-up in addition to other parameters.

Modeling correlates of low bone mineral density in patients with phenylalanine hydroxylase deficiency

Phenylalanine hydroxylase (PAH) deficiency is an inherited metabolic disorder requiring life-long restriction of dietary protein and phenylalanine-free medical food. Low bone mineral density (BMD) is reported, but factors associated with BMD Z-score (standard deviations from normal) are unknown. We examined associations between clinical and dietary parameters and total BMD Z-score in PAH deficiency patients, and developed models to predict Z-score. Data collected from patients >4 years of age (n = 88; mean age = 18.8 y; 61 % female) included demographic, clinical, laboratory, and dietary intakes. Adjusted Spearman's correlation coefficients were calculated between parameters and TBMD Z-score, measured by dual energy x-ray absorptiometry (DXA). Parameters approaching significance (p-value < 0.10) were candidate predictors for four linear regression models predicting TBMD Z-score. To validate, model-predicted Z-scores were compared to DXA Z-scores. Mean TBMD Z-score was -0.326; 18 (20.4 %) had Z-score < -1. Z-scores were positively correlated with dietary vitamin D, calcium, and medical food intake and compliance with prescription, and negatively with dietary carbohydrate, sugar, caffeine intake, glycemic load, and prescribed medical food (grams protein/day; p-value < 0.05). The best model included medical food compliance, medical food intake, caffeine intake, and bone-specific alkaline phosphatase (r-square = 0.364). This model predicted Z-score category [normal or low (<-1)] with sensitivity = 66.7 %, likelihood ratio = 14.7, and AUC = 0.83 compared to DXA Z-score. No subjects had low BMD for chronological age (Z-score ≤ -2). Compliance with medical food prescription was the strongest predictor of TBMD Z-score. One model, if validated in a separate sample of patients with more cases of low BMD, showed potential to estimate TBMD Z-score using routine clinical patient parameters.