The intake of total protein, natural protein and protein substitute and growth of height and head circumference in Dutch infants with phenylketonuria

Evaluating Therapy and Growth in Children with Phenylketonuria: A Retrospective Longitudinal Study from Two Romanian Centers

Background and Objectives: Phenylketonuria (PKU) is a rare genetic disorder characterized by the inability to convert the essential amino acid phenylalanine into tyrosine. Early dietary treatment can successfully prevent complications, but controversies still exist regarding the attainment of normal growth in these patients. Materials and Methods: Eighteen patients with PKU from two Romanian reference centers were compared to eighteen non-PKU controls, matched for age and gender. The comparisons used weight-for-height, weight-for-age, height/length-for-age, and body mass index-for-age z-scores from birth to three years of age. Results: The PKU study group consisted of nine boys and nine girls, with a median follow-up period of thirty-six months (interquartile range = 9.75). While median values of all four growth metrics remained within the normal range across the entire study period, weight-for-age z-scores were significantly lower in PKU patients throughout most of the study (p < 0.001). Conclusions: The persistent lower weight-for-age z-scores of the PKU patients compared to controls indicate that ongoing monitoring and potential adjustments in dietary therapy may be necessary to further optimize growth outcomes.

Oral enzyme therapy for maple syrup urine disease (MSUD) suppresses plasma leucine levels in intermediate MSUD mice and healthy nonhuman primates

Maple syrup urine disease (MSUD) is an inborn error of branched-chain amino acid metabolism affecting several thousand individuals worldwide. MSUD patients have elevated levels of plasma leucine and its metabolic product α-ketoisocaproate (KIC), which can lead to severe neurotoxicity, coma, and death. Patients must maintain a strict diet of protein restriction and medical formula, and periods of noncompliance or illness can lead to acute metabolic decompensation or cumulative neurological impairment. Given the lack of therapeutic options for MSUD patients, we sought to develop an oral enzyme therapy that can degrade leucine within the gastrointestinal tract prior to its systemic absorption and thus enable patients to maintain acceptable plasma leucine levels while broadening their access to natural protein. We identified a highly active leucine decarboxylase enzyme from Planctomycetaceae bacterium and used directed evolution to engineer the enzyme for stability to gastric and intestinal conditions. Following high-throughput screening of over 12 000 enzyme variants over 9 iterative rounds of evolution, we identified a lead variant, LDCv10, which retains activity following simulated gastric or intestinal conditions in vitro. In intermediate MSUD mice or healthy nonhuman primates given a whey protein meal, oral treatment with LDCv10 suppressed the spike in plasma leucine and KIC and reduced the leucine area under the curve in a dose-dependent manner. Reduction in plasma leucine correlated with decreased brain leucine levels following oral LDCv10 treatment. Collectively, these data support further development of LDCv10 as a potential new therapy for MSUD patients.

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.

Phenylalanine free infant formula in the dietary management of phenylketonuria

BACKGROUND

Phenylalanine-free infant formula is an essential source of safe protein in a phenylalanine restricted diet, but its efficacy is rarely studied. We report a multicentre, open, longitudinal, prospective intervention study on a phenylalanine-free infant formula (PKU Start: Vitaflo International Ltd.).

RESULTS

This was a 2-part study: part I (28 days short term evaluation) and part II (12 months extension). Data was collected on infant blood phenylalanine concentrations, dietary intake, growth, and gastrointestinal tolerance. Ten infants (n = 8 males, 80%), with a median age of 14 weeks (range 4-36 weeks) were recruited from 3 treatment centres in the UK. Nine of ten infants completed the 28-day follow-up (one caregiver preferred the usual phenylalanine-free formula and discontinued the study formula after day 14) and 7/9 participated in study part II. The phenylalanine-free infant formula contributed a median of 57% (IQR 50-62%) energy and 53% (IQR 33-66%) of total protein intake from baseline to the end of the part II extension study. During the 12-month follow-up, infants maintained normal growth and satisfactory blood phenylalanine control. Any early gastrointestinal symptoms (constipation, colic, vomiting and poor feeding) improved with time.

CONCLUSION

The study formula was well tolerated, helped maintain good metabolic control, and normal growth in infants with PKU. The long-term efficacy of phenylalanine-free infant formula should continue to be observed and monitored.

Complications of the Low Phenylalanine Diet for Patients with Phenylketonuria and the Benefits of Increased Natural Protein

Phenylketonuria (PKU) is an inherited disorder in which phenylalanine (Phe) is not correctly metabolized leading to an abnormally high plasma Phe concentration that causes profound neurologic damage if left untreated. The mainstay of treatment for PKU has centered around limiting natural protein in the diet while supplementing with medical foods in order to prevent neurologic injury while promoting growth. This review discusses several deleterious effects of the low Phe diet along with benefits that have been reported for patients with increased natural protein intake while maintaining plasma Phe levels within treatment guidelines.

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.

Growth and Body Composition in PKU Children-A Three-Year Prospective Study Comparing the Effects of L-Amino Acid to Glycomacropeptide Protein Substitutes

Protein quality and quantity are important factors in determining lean body (muscle) mass (LBM). In phenylketonuria (PKU), protein substitutes provide most of the nitrogen, either as amino acids (AA) or glycomacropeptide with supplementary amino acids (CGMP-AA). Body composition and growth are important indicators of long-term health. In a 3-year prospective study comparing the impact of AA and CGMP-AA on body composition and growth in PKU, 48 children were recruited. N = 19 (median age 11.1 years, range 5–15 years) took AA only, n = 16 (median age 7.3 years, range 5–15 years) took a combination of CGMP-AA and AA, (CGMP50) and 13 children (median age 9.2 years, range 5–16 years) took CGMP-AA only (CGMP100). A dual energy X-ray absorptiometry (DXA) scan at enrolment and 36 months measured LBM, % body fat (%BF) and fat mass (FM). Height was measured at enrolment, 12, 24 and 36 months. No correlation or statistically significant differences (after adjusting for age, gender, puberty and phenylalanine blood concentrations) were found between the three groups for LBM, %BF, FM and height. The change in height z scores, (AA 0, CGMP50 +0.4 and CGMP100 +0.7) showed a trend that children in the CGMP100 group were taller, had improved LBM with decreased FM and % BF but this was not statistically significant. There appeared to be no advantage of CGMP-AA compared to AA on body composition after 3-years of follow-up. Although statistically significant differences were not reached, a trend towards improved body composition was observed with CGMP-AA when it provided the entire protein substitute requirement.

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.

Over Restriction of Dietary Protein Allowance: The Importance of Ongoing Reassessment of Natural Protein Tolerance in Phenylketonuria

Phenylalanine (Phe) tolerance is highly variable in phenylketonuria (PKU) and rarely described in patients aged ≥12 years. Patients ≥12 years of age with PKU were systematically challenged with additional natural protein (NP) if blood Phe levels remained below 480 µmol/L (i.e., upper target blood Phe level for patients aged ≥12 years using Portuguese PKU guidelines). In PKU patients, NP tolerance was calculated at baseline and a median of 6 months after systematic challenge with NP whilst patients were maintaining a blood Phe ≤480 μmol/L. Anthropometry was assessed at both times. Routine blood Phe levels were collected. We studied 40 well-controlled PKU patients (10 hyperphenylalaninemia (HPA), 23 mild and 7 classic PKU), on a low-Phe diet with a mean age of 17 years (12–29 years). Median daily NP intake significantly increased between assessments (35 vs. 40 g/day, p = 0.01). Twenty-six patients (65%) were able to increase their median NP intake by a median 12 g/day (2–42 g)/day and still maintain blood Phe within target range. Out of the previous 26 patients, 20 (77%) (8 HPA, 11 mild and 1 classical PKU) increased NP from animal sources (e.g., dairy products, fish and meat) and 6 patients (23%) (3 mild and 3 classical PKU) from plant foods (bread, pasta, potatoes). Median protein equivalent intake from Phe-free/low-Phe protein substitute decreased (0.82 vs. 0.75 g/kg, p = 0.01), while median blood Phe levels remained unchanged (279 vs. 288 μmol/L, p = 0.06). Almost two-thirds of patients with PKU tolerated additional NP when challenged and still maintained blood Phe within the national target range. This suggests that some patients with PKU treated by a low-Phe diet only may over restrict their NP intake. In order to minimise the burden of treatment and optimise NP intake, it is important to challenge with additional NP at periodic intervals.

Growth, Protein and Energy Intake in Children with PKU Taking a Weaning Protein Substitute in the First Two Years of Life: A Case-Control Study

Growth issues have been observed in young children with phenylketonuria (PKU), but studies are conflicting. In infancy, there is an increasing trend to introduce a second-stage semi-solid weaning protein substitute (WPS) but there is concern that this may not meet energy requirements. In this longitudinal, prospective study, 20 children with PKU transitioning to a WPS, and 20 non-PKU controls were observed monthly from weaning commencement (4–6 months) to 12 m and at 15, 18 and 24 months of age for: weight, length, head circumference, body mass index (BMI), energy and macronutrient intake. Growth parameters were within normal range at all ages in both groups with no significant difference in mean z-scores except for accelerated length in the PKU group. No child with PKU had z-scores < −2 for any growth parameter at age 2 years. Total protein and energy intake in both groups were similar at all ages; however, from 12–24 months in the PKU group, the percentage of energy intake from carbohydrate increased (60%) but from fat decreased (25%) and inversely for controls (48% and 36%). In PKU, use of low volume WPS meets Phe-free protein requirements, facilitates transition to solid foods and supports normal growth. Further longitudinal study of growth, body composition and energy/nutrient intakes in early childhood are required to identify any changing trends.

Early feeding practices in infants with phenylketonuria across Europe

Background

In infants with phenylketonuria (PKU), dietary management is based on lowering and titrating phenylalanine (Phe) intake from breast milk or standard infant formula in combination with a Phe-free infant formula in order to maintain blood Phe levels within target range. Professionals use different methods to feed infants with PKU and our survey aimed to document practices across Europe.

Methods

We sent a cross sectional, survey monkey® questionnaire to European health professionals working in IMD. It contained 31 open and multiple-choice questions. The results were analysed according to different geographical regions.

Results

Ninety-five centres from 21 countries responded. Over 60% of centres commenced diet in infants by age 10 days, with 58% of centres implementing newborn screening by day 3 post birth. At diagnosis, infant hospital admission occurred in 61% of metabolic centres, mainly in Eastern, Western and Southern Europe. Breastfeeding fell sharply following diagnosis with only 30% of women still breast feeding at 6 months.

53% of centres gave pre-measured Phe-free infant formula before each breast feed and 23% alternated breast feeds with Phe-free infant formula. With standard infant formula feeds, measured amounts were followed by Phe-free infant formula to satiety in 37% of centres (n = 35/95), whereas 44% (n = 42/95) advised mixing both formulas together. Weaning commenced between 17 and 26 weeks in 85% centres, ≥26 weeks in 12% and < 17 weeks in 3%.

Discussion

This is the largest European survey completed on PKU infant feeding practices. It is evident that practices varied widely across Europe, and the practicalities of infant feeding in PKU received little focus in the PKU European Guidelines (2017). There are few reports comparing different feeding techniques with blood Phe control, Phe fluctuations and growth. Controlled prospective studies are necessary to assess how different infant feeding practices may influence longer term feeding development.

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.

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.

Practices in prescribing protein substitutes for PKU in Europe: No uniformity of approach

BACKGROUND

There appears little consensus concerning protein requirements in phenylketonuria (PKU).

METHODS

A questionnaire completed by 63 European and Turkish IMD centres from 18 countries collected data on prescribed total protein intake (natural/intact protein and phenylalanine-free protein substitute [PS]) by age, administration frequency and method, monitoring, and type of protein substitute. Data were analysed by European region using descriptive statistics.

RESULTS

The amount of total protein (from PS and natural/intact protein) varied according to the European region. Higher median amounts of total protein were prescribed in infants and children in Northern Europe (n=24 centres) (infants <1 year, >2-3g/kg/day; 1-3 years of age, >2-3 g/kg/day; 4-10 years of age, >1.5-2.5 g/kg/day) and Southern Europe (n=10 centres) (infants <1 year, 2.5 g/kg/day, 1-3 years of age, 2 g/kg/day; 4-10 years of age, 1.5-2 g/kg/day), than by Eastern Europe (n=4 centres) (infants <1 year, 2.5 g/kg/day, 1-3 years of age, >2-2.5 g/kg/day; 4-10 years of age, >1.5-2 g/kg/day) and with Western Europe (n=25 centres) giving the least (infants <1 year, >2-2.5 g/kg/day, 1-3 years of age, 1.5-2 g/kg/day; 4-10 years of age, 1-1.5 g/kg/day). Total protein prescription was similar in patients aged >10 years (1-1.5 g/kg/day) and maternal patients (1-1.5 g/kg/day).

CONCLUSIONS

The amounts of total protein prescribed varied between European countries and appeared to be influenced by geographical region. In PKU, all gave higher than the recommended 2007 WHO/FAO/UNU safe levels of protein intake for the general population.

New insights in growth of phenylketonuric patients

Treatment of phenylketonuria involves a restriction in the intake of natural proteins. This can lead to growth impairment. Weight, height and body mass index of 109 hyperphenylalaninemic patients (mild hyperphenylalaninemia (HPA) and phenylketonuria (PKU)) were determined from birth until 18 years, every 6 months, and differences to the healthy population, depending on the age, sex and phenotype, were analyzed. Data collection was longitudinal retrospective during 31 years. Statistical analysis of z-score values was performed by advanced statistical tools. Long-term evolution of anthropometric z-scores showed no significant statistical differences between PKU and mild HPA individuals, according to the general population. For PKU individuals, height is slightly lower and weight slightly higher than in the healthy population, but differences are smaller than one standard deviation. Nevertheless, over-time evolutions of female height z-scores are different in each type of pathology, with a crossover between 8 and 12 years (p = 0.0186).

CONCLUSIONS

It is nowadays possible to achieve a long-term normal growth in PKU patients with appropriate dietary treatment. There is however an acceleration of growth up to 8 years old for PKU female patients that leads to a slightly lower final height. Detection of this behaviour was possible by using nonlinear mixed effects models.

Protein substitute for children and adults with phenylketonuria

BACKGROUND

Phenylketonuria is an inherited metabolic disorder characterised by an absence or deficiency of the enzyme phenylalanine hydroxylase. The aim of treatment is to lower blood phenylalanine concentrations to the recommended therapeutic range to prevent developmental delay and support normal growth. Current treatment consists of a low-phenylalanine diet in combination with a protein substitute which is free from or low in phenylalanine. Guidance regarding the use, dosage, and distribution of dosage of the protein substitute over a 24-hour period is unclear, and there is variation in recommendations among treatment centres. This is an update of a Cochrane review first published in 2005, and previously updated in 2008.

OBJECTIVES

To assess the benefits and adverse effects of protein substitute, its dosage, and distribution of dose in children and adults with phenylketonuria who are adhering to a low-phenylalanine diet.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group Trials Register which consists of references identified from comprehensive electronic database searches and hand searches of relevant journals and abstract books of conference proceedings. We also contacted manufacturers of the phenylalanine-free and low-phenylalanine protein substitutes for any data from published and unpublished randomised controlled trials.Date of the most recent search of the Group's Inborn Errors of Metabolism Trials Register: 03 April 2014.

SELECTION CRITERIA

All randomised or quasi-randomised controlled trials comparing: any dose of protein substitute with no protein substitute; an alternative dosage; or the same dose, but given as frequent small doses throughout the day compared with the same total daily dose given as larger boluses less frequently.

DATA COLLECTION AND ANALYSIS

Both authors independently extracted data and assessed trial quality.

MAIN RESULTS

Three trials (69 participants) are included in this review. One trial investigated the use of protein substitute in 16 participants, while a further two trials investigated the dosage of protein substitute in a total of 53 participants. Due to issues with data presentation in each trial, described in full in the review, formal statistical analyses of the data were impossible. Investigators will be contacted for further information.

AUTHORS' CONCLUSIONS

No conclusions could be drawn about the short- or long-term use of protein substitute in phenylketonuria due to the lack of adequate or analysable trial data. Additional data and randomised controlled trials are needed to investigate the use of protein substitute in phenylketonuria. Until further evidence is available, current practice in the use of protein substitute should continue to be monitored with care.

New ways of defining protein and energy relationships in inborn errors of metabolism

Dietary restrictions required to manage individuals with inborn errors of metabolism (IEM) are essential for metabolic control, however may result in an increased risk to both short and long-term nutritional status. Dietary factors most likely to influence nutritional status include energy intake, protein quality and quantity, micronutrient intake and the frequency and extent to which the diet must be altered during periods of increased physical or metabolic stress. Patients on the most restrictive diets, including those with intakes consisting of low levels of natural protein or those with recurrent illness or frequent metabolic decompensation carry the most nutritional risk. Due to the difficulties in determining condition specific requirements, dietary intake recommendations and nutritional monitoring tools used in patients with IEM are the same as, or extrapolated from, those used in healthy populations. As a consequence, evidence is lacking for the safest dietary prescriptions required to manage these patients long term, as tolerance to dietary therapy is generally described in terms of metabolic stability rather than long term nutritional and health outcomes. As the most frequent therapeutic dietary manipulation in IEM is alteration in dietary protein, and as protein status is critically dependent on adequate energy provision, the use of a Protein to Energy ratio (P:E ratio) as an additional tool will better define the relationship between these critical components. This could accurately define dietary quality and ensure that not only an adequate, but also a safe and balanced intake is provided.

Chronic kidney disease in adolescent and adult patients with phenylketonuria

OBJECTIVES

A lifelong phenylalanine-restricted diet with supplementation of a phenylalanine-free amino acid formula is recommended in patients with phenylketonuria (PKU). The effect of a long-term PKU diet on renal function and blood pressure has not been investigated yet.

DESIGN

We analyzed renal function in 67 patients with PKU, aged 15-43 years, by measuring glomerular filtration rate (GFR) and effective renal plasma flow by isotope clearance ((51)Cr-EDTA, (123)J-Hippuran), estimated GFR, blood retention parameters, urinary protein and electrolyte excretion. Renal ultrasound and 24 h ambulatory blood pressure monitoring were performed additionally. Patients were divided into three groups according to their: 1) current diet (CD), i.e., daily protein intake: ICD <0.8 g/kg, IICD 0.8-1.04 g/kg, IIICD >1.04 g/kg; 2) life-long diet time (LDT), i.e., cumulative years of life in which daily protein intake exceeded dietary recommendations: ILDT <15 years, IILDT 15-19 years, IIILDT >19 years.

RESULTS

GFR was decreased in 19 % of the patients. With increasing protein intake, GFR decreased significantly (ICD 111 ml/min; IICD 105 ml/min; IIICD 99 ml/min. ILDT 112 ml/min; IILDT 103 ml/min; IIILDT 99 ml/min). Proteinuria was detected in 31 %, microalbuminuria in 7 %, and hypercalciuria in 23 % of the patients. 23 % of the patients had arterial hypertension, and 41 % revealed a nocturnal non-dipping status.

CONCLUSIONS

In patients with PKU on a lifelong diet we could detect impaired renal function in 19 %, proteinuria in 31 %, and arterial hypertension in 23 %. Thus, chronic kidney disease may develop in PKU patients, and routine renal function tests should be performed during long-term follow-up.

Tetrahydrobiopterin therapy vs phenylalanine-restricted diet: impact on growth in PKU

BACKGROUND

Treatment of phenylketonuria based upon strict vegetarian diets, with very low phenylalanine intake and supplemented by phenylalanine-free formula, has proven to be effective in preventing the development of long-term neurological sequelae due to phenylalanine accumulation. On the other hand, such diets have occasionally been reported to hinder normal development, some individuals presenting with growth retardation. Tetrahydrobiopterin therapy has opened up new treatment options for a significant proportion of phenylketonuric patients, enabling them to eat normal diets and be freed from the need to take synthetic supplements. However, little is known about how this therapy affects their physical development.

METHODS

We conducted a retrospective longitudinal study examining anthropometric characteristics (height, weight, body mass index and growth speed Z-scores) in a cohort of phenylketonuric patients on tetrahydrobiopterin therapy (38 subjects) comparing their characteristics with those of a group of phenylketonuric patients on phenylalanine-restricted diets (76 subjects). Nutritional issues were also considered, to further explore the possibility of higher natural protein intake being associated with better physical development. Data were collected every six months over two different periods of time (two or five years).

RESULTS

No improvement was observed in the aforementioned anthropometric variables in the cohort on tetrahydrobiopterin therapy, from prior to starting treatment to when they had been taking the drug for two or five years. Rather, in almost all cases there was a fall in the mean Z-score for the variables during these periods, although the changes were not significant in any case. Further, we found no statistically differences between the two groups at any considered time point. Growth impairment was also noted in the phenylketonuric patients on low-phenylalanine diets. Individuals on tetrahydrobiopterin therapy increased their natural protein intake and, in some instances, this treatment enabled individuals to eat normal diets, with protein intake meeting RDAs. No association was found, however, between higher protein intake and growth.

CONCLUSION

Our study identified growth impairment in patients with phenylketonuria on tetrahydrobiopterin, despite higher intakes of natural proteins. In fact, individuals undergoing long-term tetrahydrobiopterin treatment seemed to achieve similar developmental outcomes to those attained by individuals on more restricted diets.

Early dietary treated patients with phenylketonuria can achieve normal growth and body composition

BACKGROUND

In the past, overtreatment may have resulted in growth impairment in patients with phenylketonuria.

OBJECTIVE

The paper aims to investigate height and body composition in early treated patients with phenylketonuria who were diagnosed between 1981 and 2008.

DESIGN

A cross-sectional study of 89 patients with phenylketonuria and 78 controls aged (mean ± SD, in years) 14.4 ± 6.6 and 15.9 ± 7.1, respectively, was undertaken, including anthropometric and body composition evaluation using bioelectrical impedance. Median Phe concentrations in the last year before study enrollment were used as a measure of metabolic control. Natural protein and amino acid mixture intakes were recorded in patients.

RESULTS

No statistically significant differences were found on height z-scores between patients and controls aged less than 19 years (p=0.301), although all patients with classical phenylketonuria revealed negative height z-scores, resulting in a mean ± SD of -0.65 ± 0.41. Among participants aged 19 years or more, median (p25-p75) of height was significantly higher in controls [168.0 cm (159.2-174.8)] than in patients [160.5 cm (151.9-167.5)] (p=0.017). No significant differences were found between patients and controls regarding fat mass, fat free mass, muscular mass, body cell mass index and phase angle.

CONCLUSION

Our results suggest that early and continuously treated patients with phenylketonuria born after 1992 can achieve normal growth and body composition, although the negative height z-score in patients with classical phenylketonuria strengthens the continuous need to optimize the quality of their protein intake.

Physical development in patients with phenylketonuria on dietary treatment: a retrospective study

OBJECTIVES

To evaluate the growth and physical development in patients with phenylalanine hydroxylase deficiency who follow exclusively dietary treatment.

METHODS

Anthropometric measurements of 160 patients with hyperphenylalaninemia who were followed at our center over a 25 year period were obtained. Only patients treated exclusively with a protein-restrictive diet supplemented with amino acid mixtures were included. Height, weight and body mass index were measured at birth, at diagnosis, at 6 and 12 months of age, and annually until 18 years of age in patients with phenylketonuria or until 9 years of age in patients with mild hyperphenylalaninemia and compared to official national reference values. The final height of PKU patients was also compared to their expected family height.

RESULTS

The analysis of z scores suggested no significant differences in physical development between PKU patients and the healthy population during the study period. The final height of PKU patients revealed that they were 2 to 4 cm taller than expected when compared to the mean family height (p<0.001). The mean weight and BMI at puberty suggested that many patients with severe PKU, but not other phenotypes, were overweight during this period.

CONCLUSION

Physical development can be optimal in PKU patients regardless of their phenotype and the severity of the diet. A tendency to excessive weight gain is seen in adolescence in the most severe phenotypes.

Mild hyperphenylalaninemia: to treat or not to treat

One of the issues to be resolved in phenylketonuria is whether patients with mild hyperphenylalaninemia need treatment, or in other words, in what patients treatment needs to be started. Do patients need treatment when phenylalanine concentrations in blood are >360 μmol/L or >600 μmol/L? This paper reviews the literature on the outcome of untreated patients with mild hyperphenylalaninemia to try to determine whether outcome is normal. The paper concludes that there is, in fact, only one paper that can be used to answer this question. Therefore, the question is whether we may rely on one paper to draw conclusions or whether more research is necessary to determine whether all patients with phenylalanine concentrations >360 μmol/L or all patients with phenylalanine concentrations >600 μmol/L require treatment.

Tetrahydrobiopterin therapy for phenylketonuria in infants and young children

OBJECTIVE

To describe patient selection, treatment administration, response evaluation, and side effect management associated with sapropterin therapy in infants and children aged <4 years.

STUDY DESIGN

Six case reports are presented from 4 US metabolic clinics treating phenylketonuria with sapropterin in patients aged 7 months to 4 years. Outcomes included blood phenylalanine (Phe) levels before and during treatment. For 3 of 6 cases, diet records were used to monitor changes in dietary Phe.

RESULTS

Severity of phenylketonuria ranged from mild to severe (classic). Treatment with sapropterin was safe and generally well tolerated. Blood Phe levels were reduced, or maximum dietary Phe tolerance was increased in patients with blood Phe that was well controlled by diet.

CONCLUSIONS

Given the increasing evidence that maintaining blood Phe levels below 360 μmol/L is important for the normal development of neurocognitive and behavioral function, sapropterin can be combined with a Phe-restricted diet to control blood Phe levels in young patients responsive to sapropterin therapy.

Diurnal variations in blood phenylalanine of PKU infants under different feeding regimes

In phenylketonuria (PKU) patients, diurnal fluctuations of blood phenylalanine (Phe) are different from healthy individuals. Until now this pattern has been studied in PKU patients over one year of age.

OBJECTIVE

The aim of this observational study was to investigate diurnal patterns in PKU infants under one year of age receiving both the natural protein and Phe-free formula at the same time or in an alternating feeding scheme.

METHODS

In 7 PKU infants (aged 3-8 months), diurnal variations in blood Phe concentrations were recorded: on day A they received natural protein and Phe-free formula combined in each feeding; on day B they received these in an alternating feeding scheme. The number of feedings, total protein, and energy intake was similar on both study days. Blood samples were taken before each feeding.

RESULTS

The means (± SD) of the difference between the individual minimum and maximum blood Phe concentrations were 81(± 50) μmol/L and 104(± 26) μmol/L on days A and B, respectively (n.s.). Fifty and 30% of the samples were below target range for age (120 μmol/L), while only 3% and 6% were above target range (360 μmol/L) on days A and B respectively (n.s.).

CONCLUSION

Both feeding regimes, i.e. the natural protein and Phe-free formula combined in each feeding or alternating, resulted in comparable diurnal fluctuations of blood Phe concentrations.

Adult phenylketonuria outcome and management

The problem to evaluate treatment outcome in adult PKU (phenylketonuric) patients lies in the heterogeneity of the adult PKU population. This heterogeneity is not only based on the different treatment history of every individual patient but also on the different severity of the underlying defect of the enzyme phenylalanine hydroxylase. Recent, partly double blind studies in adult PKU patients further support recommendation for lifelong treatment. However, it has become evident that dietary treatment is suboptimal and continuation to adulthood often not accepted. Late detected PKU patients (up to 4-6 years of age) benefit from strict dietary treatment and are able to catch up in intellectual performance. Untreated, severely retarded patients with behavioral changes may benefit from introduction of dietary treatment. However, individual decision is necessary and based on the personal situation of the patient. In early and well treated patients a number of studies have demonstrated that cognitive and neurosychologic tests are different from controls. In addition there is evidence that patients with higher blood phenylalanine (phe) levels demonstrate more often psychiatric symptoms like depression and anxiety. Medical problems are more often observed: there are certain risks as impaired growth, decreased bone mineral density and nutrional deficits probably caused by dietary treatment with an artificial protein substitute and/or missing compliance with an unpleasant diet. The long term risk of a strict dietary treatment must be balanced with the risk of higher blood phe (mean blood phenylalanine >600-900 μmol/L) on cognitive and neuropsychological functions and psychiatric symptoms. Further studies should consider the role of blood phe exposure for brain development in childhood and for brain function in all ages. Besides mean blood phe, fluctuation of blood phe over time is important. Fluctuation of blood phe is decreased by sapropterin treatment in responsive patients which would on the long term may have positive effects on cognitive outcome. Further studies also should include adult PKU patients.

Nutrition in phenylketonuria

The same basic principles are used to deliver dietary treatment in PKU that was developed sixty years ago. Dietary treatment is undoubtedly very successful, but it has gradually evolved and been guided commonly by individual experience and expert opinion only. There is little international consensus about dietary practice with improvements in specialist dietary products concentrating on taste and presentation rather than nutritional composition. Many areas of dietary treatment have not been rigorously examined. In particular, the amino acid and micronutrient profile of Phenylalanine-free (phe-free) amino acids requires further study. In different formulations of phe-free amino acids, there are variations in the amino acid patterns as well the amount of essential and non essential amino acids per 100g/amino acids. The amount of added tyrosine and branch chain amino varies substantially, and in PKU specifically, there is little data about their relative absorption rates and bioavailability. In phe-free amino acids, there is evidence suggesting that some of the added micronutrients may be excessive and so the source and amount of each micronutrient should be scrutinized, with a need for the development of international nutritional composition standards exclusively for these products. There is a dearth of data about the life-long phenylalanine tolerance of patients or the nutritional state of adult patients treated with diet. There is a growing need to measure body composition routinely in children with PKU and with the rise in childhood obesity, it is important to measure body fatness and identify those who are at greatest risk of 'co-morbidities' of obesity. There is necessity for international collaboration to ensure robust data is collected on many basic aspects of nutritional care to guarantee that diet therapy is delivered to the highest standard.

Suboptimal outcomes in patients with PKU treated early with diet alone: revisiting the evidence

BACKGROUND

The National Institute of Health (NIH) published a Consensus Statement on the screening and management of Phenylketonuria (PKU) in 2000. The panel involved in the development of this consensus statement acknowledged the lack of data regarding the potential for more subtle suboptimal outcomes and the need for further research into treatment options. In subsequent years, the approval of new treatment options for PKU and outcome data for patients treated from the newborn period by dietary therapy alone have become available. We hypothesized that a review of the PKU literature since 2000 would provide further evidence related to neurocognitive, psychosocial, and physical outcomes that could serve as a basis for reassessment of the 2000 NIH Consensus Statement.

METHODS

A systematic review of literature residing in PubMed, Scopus and PsychInfo was performed in order to assess the outcome data over the last decade in diet-alone early-treated PKU patients to assess the need for new recommendations and validity of older recommendations in light of new evidence.

RESULTS

The majority of publications (140/150) that contained primary outcome data presented at least one suboptimal outcome compared to control groups or standardized norms/reference values in at least one of the following areas: neurocognitive/psychosocial (N=60; 58 reporting suboptimal outcomes); quality of life (N=6; 4 reporting suboptimal outcomes); brain pathology (N=32; 30 reporting suboptimal outcomes); growth/nutrition (N=34; 29 reporting suboptimal outcomes); bone pathology (N=9; 9 reporting suboptimal outcomes); and/or maternal PKU (N=19; 19 reporting suboptimal outcomes).

CONCLUSIONS

Despite the remarkable success of public health programs that have instituted newborn screening and early introduction of dietary therapy for PKU, there is a growing body of evidence that suggests that neurocognitive, psychosocial, quality of life, growth, nutrition, bone pathology and maternal PKU outcomes are suboptimal. The time may be right for revisiting the 2000 NIH Consensus Statement in order to address a number of important issues related to PKU management, including treatment advancements for metabolic control in PKU, blood Phe variability, neurocognitive and psychological assessments, routine screening measures for nutritional biomarkers, and bone pathology.

Protein substitute for children and adults with phenylketonuria

BACKGROUND

Phenylketonuria is an inherited metabolic disorder characterised by an absence or deficiency of the enzyme phenylalanine hydroxylase. The aim of treatment is to lower blood phenylalanine concentrations to the recommended therapeutic range to prevent developmental delay and support normal growth. Current treatment consists of a low-phenylalanine diet in combination with a protein substitute which is free from or low in phenylalanine. Guidance regarding the use, dosage, and distribution of dosage of the protein substitute over a 24-hour period is unclear, and there is variation in recommendations among treatment centres.

OBJECTIVES

To assess the benefits and adverse effects of protein substitute, its dosage, and distribution of dose in children and adults with phenylketonuria who are adhering to a low-phenylalanine diet.

SEARCH STRATEGY

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group Trials Register which consists of references identified from comprehensive electronic database searches and hand searches of relevant journals and abstract books of conference proceedings. We also contacted manufacturers of the phenylalanine-free and low-phenylalanine protein substitutes for any data from published and unpublished randomised controlled trials.Date of the most recent search of the Group's Trials Register: April 2008.

SELECTION CRITERIA

All randomised or quasi-randomised controlled trials comparing: any dose of protein substitute with no protein substitute; an alternative dosage; or the same dose, but given as frequent small doses throughout the day compared with the same total daily dose given as larger boluses less frequently.

DATA COLLECTION AND ANALYSIS

Both authors independently extracted data and assessed trial quality.

MAIN RESULTS

Three trials (69 participants) are included in this review. One trial investigated the use of protein substitute in 16 participants, while a further two trials investigated the dosage of protein substitute in a total of 53 participants. Due to issues with data presentation in each trial, described in full in the review, formal statistical analyses of the data were impossible. Investigators are being contacted for further information.

AUTHORS' CONCLUSIONS

No conclusions could be drawn about the short- or long-term use of protein substitute in phenylketonuria due to the lack of adequate or analysable trial data. Additional data and randomised controlled trials are needed to investigate the use of protein substitute in phenylketonuria. Until further evidence is available, current practice in the use of protein substitute should continue to be monitored with care.

Phenylketonuria: questioning the gospel

Phenylketonuria (PKU) was first described over 70 years ago, treatment was developed 50 years ago and universal newborn PKU screening was introduced 40 years ago. Phenylalanine-restricted dietary treatment has prevented mental retardation in thousands of individuals worldwide. We acknowledge, however, that there is still much to learn in the field. The incidence of mental retardation in untreated PKU is likely to be considerably less than the original estimates. Since dietary control is suboptimal in late childhood, adolescence and adulthood, alternative methods of treatment are being explored. These include large neutral amino acids, phenylalanine ammonia lyase, tetrahydrobiopterin and gene replacement. Evidence has surfaced that the semisynthetic, low-protein diet used to treat PKU may be deficient in certain important nutrients. Maternal PKU treatment may be successful even if initiated as late as 8-10 weeks into pregnancy. A plea is made for the immediate establishment of adult treatment centers for PKU (and other inherited metabolic diseases) for long-term treatment, follow-up and research.

Growth and body composition in children with classical phenylketonuria: results in 34 patients and review of the literature

Treatment of phenylketonuria (PKU, OMIM 261600) means a diet restricted in natural protein and supplemented with phenylalanine (Phe)-free L-amino acid mixtures. Growth impairment has been described even in patients with a total protein intake at or above the recommended dietary allowance (RDA). In the present study, growth and body composition (fat-free mass (FFM) and fat) were recorded over 12 months in 34 treated PKU patients (mean age 8.7 years at baseline). Measurements were compared with those of healthy peers and with general population standard (Z-) scores calculated using the LMS method. In 28 PKU patients, data on birth weight and birth length were available and related to measurements at baseline of the study. Mean total protein intake in PKU patients was 124% (range 77-193%) of the RDA (DACH 2000). No significant differences in growth and body composition were present between PKU patients and healthy populations either at birth or during the study period. The significant correlation of FFM (representing muscle mass) with intake of natural protein--rather than total protein--indicates that the enhancement of tolerance to natural protein may be of value in PKU patients.

Protein metabolism in adult patients with phenylketonuria

OBJECTIVE

Protein intake recommendations in phenylketonuria (PKU) are frequently the subject of discussion. For healthy adults, the recommended daily allowance (RDA) is 0.8 g.kg(-1).d(-1), which is generally lower than that observed in the general Western population. We investigated whether whole-body protein metabolism in patients with PKU is comparable to that of healthy controls at a RDA rate of protein intake.

METHODS

Six adult patients with well-controlled PKU and six healthy subjects of comparable age, height, and weight were studied using a primed continuous infusion of [1-(13)C]-valine for 8 h after an overnight fast before and during frequent meals. Normal protein was given to controls, whereas patients with PKU received a combination of an amino acid mixture and natural protein.

RESULTS

No significant differences were observed between patients with PKU and controls in preprandial and prandial rates of valine appearance and oxidation and protein breakdown, protein synthesis, and net protein balance. Feeding resulted in a significant (P < 0.01) decrease in protein breakdown (PKU: 94 +/- 15 micromol.kg(-1).h(-1) preprandial to 49 +/- 10 micromol.kg(-1).h(-1) prandial; controls: 97 +/- 10 micromol.kg(-1).h(-1) preprandial to 55 +/- 10 micromol.kg(-1).h(-1) prandial), whereas no effects were observed in protein synthesis (PKU: 77 +/- 10 micromol.kg(-1).h(-1) preprandial to 73 +/- 7 micromol.kg(-1).h(-1) prandial; controls: 76 +/- 8 micromol.kg(-1).h(-1) preprandial to 71 +/- 5 micromol.kg(-1).h(-1) prandial). Net protein balance increased from negative prandial to positive preprandial values (PKU: -17 +/- 6 micromol.kg(-1).h(-1) preprandial to +23 +/- 8 micromol.kg(-1).h(-1) prandial; controls: -21 +/- 4 micromol.kg(-1).h(-1) preprandial to +16 +/- 9 micromol.kg(-1).h(-1) prandial).

CONCLUSION

Whole-body protein metabolism in adult patients with PKU is fully comparable to that in healthy controls at the RDA level of protein intake.

Phenylketonuria: dietary and therapeutic challenges

PKU subjects need special attention in the definition of optimal supplementation of nutrients, which may be insufficient in relation to the type of diet and may otherwise manifest symptoms of deficit. In particular, it is necessary to pay great attention to the long-chain polyunsaturated fatty acid (LC-PUFA) levels in relation to correct development of the central nervous system. On the basis of numerous beneficial effects currently known, a permanent supplementation with LC-PUFAs, in particular with docosahexaenoic acid, should be considered. Moreover, new formulas, Phe-free peptides, and 'modulated' amino acid preparations might help in preventing nutritional deficiencies and imbalances, with the ultimate aim of improving growth. New strategies--such as supply of tetrahydrobiopterin--need to be optimized in terms of targets, patients and expected outcomes.