Fifteen years of using a second stage protein substitute for weaning in phenylketonuria: a retrospective study

Phenylalanine hydroxylase deficiency treatment and management: A systematic evidence review of the American College of Medical Genetics and Genomics (ACMG)

PURPOSE

Elevated serum phenylalanine (Phe) levels due to biallelic pathogenic variants in phenylalanine hydroxylase (PAH) may cause neurodevelopmental disorders or birth defects from maternal phenylketonuria. New Phe reduction treatments have been approved in the last decade, but uncertainty on the optimal lifespan goal Phe levels for patients with PAH deficiency remains.

METHODS

We searched Medline and Embase for evidence of treatment concerning PAH deficiency up to September 28, 2021. Risk of bias was evaluated based on study design. Random-effects meta-analyses were performed to compare IQ, gestational outcomes, and offspring outcomes based on Phe ≤ 360 μmol/L vs > 360 μmol/L and reported as odds ratio and 95% CI. Remaining results were narratively synthesized.

RESULTS

A total of 350 studies were included. Risk of bias was moderate. Lower Phe was consistently associated with better outcomes. Achieving Phe ≤ 360 μmol/L before conception substantially lowered the risk of negative effect to offspring in pregnant individuals (odds ratio = 0.07, 95% CI = 0.04-0.14; P < .0001). Adverse events due to pharmacologic treatment were common, but medication reduced Phe levels, enabling dietary liberalization.

CONCLUSIONS

Reduction of Phe levels to ≤360 μmol/L through diet or medication represents effective interventions to treat PAH deficiency.

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.

Transitioning of protein substitutes in patients with phenylketonuria: evaluation of current practice

Background

In children with phenylketonuria (PKU), transitioning protein substitutes at the appropriate developmental age is essential to help with their long-term acceptance and ease of administration. We assessed the parental experiences in transitioning from a second stage to third stage liquid or powdered protein substitute in patients with PKU.

Results

Sixteen interviews (23 open-ended questions) were carried out with parents/caregivers of children with PKU (8 females, 50%) with a median age of 8 years (range 5–11 years), continuously treated with diet, and on a third stage protein substitute. Parents/caregivers identified common facilitators and barriers during the third stage protein substitute transition process. The main facilitators were: child and parent motivation, parent knowledge of the transition process, a role model with PKU, low volume and easy preparation of the third stage protein substitute (liquid/powder), anticipation of increasing child independence, lower parent workload, attractive packaging, better taste and smell, school and teacher support, dietetic plans and guidance, PKU social events, child educational materials and written resources. The main barriers were child aversion to new protein substitutes, poor child behaviour, child aged > 5 years, parental fear of change, the necessity for  parental time and persistence, loss of parental control, high product volume, different taste, smell, and texture of new protein substitutes, and peer bullying.

Conclusion

A stepwise, supportive approach is necessary when transitioning from second to third stage protein substitutes in PKU. Future studies are needed to develop guidance to assist parents/caregivers, health professionals, and teachers during the transition process.

Breastfeeding in Phenylketonuria: Changing Modalities, Changing Perspectives

Phenylketonuria (PKU) management aims to control phenylalanine (Phe) intakes. In newborns and infants this implies possible titration of Human milk (HM) with supplementation of Phe-free formula. HM benefits, better if prolonged, are well known in healthy populations, suggesting it may be used in PKU patients. Despite that, the current literature does not define recommendations on how best perform it in such a population. The main purpose of this study was to evaluate nutrition approaches in newborns and infants affected by PKU and to define if differences can influence the duration of breastfeeding. Data from 42 PKU infants were reviewed. Of these, 67% were breastfed with the use of three different approaches. The type of approach used impacted the duration of breastfeeding, which was longer when using a pre-measured amount of Phe-free formula administered prior to HM. This is the first study to suggest a specific method for breastfeeding in PKU. Considering widely known breastfeeding benefits, both for patients and their mothers, our data should encourage adequate awareness on how to choose correct breastfeeding modalities.

Protein Substitutes in PKU; Their Historical Evolution

Protein substitutes developed for phenylketonuria (PKU) are a synthetic source of protein commonly based on L-amino acids. They are essential in the treatment of phenylketonuria (PKU) and other amino acid disorders, allowing the antagonistic amino acid to be removed but with the safe provision of all other amino acids necessary for maintaining normal physiological function. They were first formulated by a chemist and used experimentally on a 2-year-old girl with PKU and their nutritional formulations and design have improved over time. Since 2008, a bioactive macropeptide has been used as a base for protein substitutes in PKU, with potential benefits of improved bone and gut health, nitrogen retention, and blood phenylalanine control. In 2018, animal studies showed that physiomimic technology coating the amino acids with a polymer allows a slow release of amino acids with an improved physiological profile. History has shown that in PKU, the protein substitute's efficacy is determined by its nutritional profile, amino acid composition, dose, timing, distribution, and an adequate energy intake. Protein substitutes are often given little importance, yet their pharmacological actions and clinical benefit are pivotal when managing PKU.

PKU dietary handbook to accompany PKU guidelines

BACKGROUND

Phenylketonuria (PKU) is an autosomal recessive inborn error of phenylalanine metabolism caused by deficiency in the enzyme phenylalanine hydroxylase that converts phenylalanine into tyrosine.

MAIN BODY

In 2017 the first European PKU Guidelines were published. These guidelines contained evidence based and/or expert opinion recommendations regarding diagnosis, treatment and care for patients with PKU of all ages. This manuscript is a supplement containing the practical application of the dietary treatment.

CONCLUSION

This handbook can support dietitians, nutritionists and physicians in starting, adjusting and maintaining dietary treatment.

Mealtime Anxiety and Coping Behaviour in Parents and Children During Weaning in PKU: A Case-Control Study

Solid food introduction may create anxiety for parents of children with phenylketonuria (PKU) due to the burden associated with protein substitute (PS) administration and natural protein restriction. In a longitudinal, prospective study, 20 mothers of children with PKU and 20 non-PKU control mothers completed 4 questionnaires (mealtime emotions, feed-time, Beck’s anxiety inventory and the coping health inventory for parents), examining parent/child mealtime emotions, anxiety, stress and coping strategies at child ages: weaning start, 8 months (m), 12 m, 15 m, 18 m and 24 m. Overall, mothers of children with PKU cope well with solid food introduction when applying a low-phenylalanine diet, with comparable low levels of stress and anxiety reported in both PKU and non-PKU groups. However, mothers of children with PKU reported peak scores in anxiety for emotive/cognitive symptoms at a child age of 15 m, and higher use of coping strategies at 15 m and 24 m (p < 0.05) of age. Generally, there was a trend that maternal anxiety regarding child rejection of PS increased with time, peaking between 12–24 m. In PKU, a child age of 12–18 m is identified as a key period when mothers feel most anxious/stressed with feeding, coinciding with raised blood phenylalanine levels probably associated with teething, illness and developing independence. Health professionals should be conscious of this vulnerable period and be prepared to offer more directional support as required.

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.

How Does Feeding Development and Progression onto Solid Foods in PKU Compare with Non-PKU Children During Weaning?

Weaning is complex for children with phenylketonuria (PKU). Breastmilk/infant formula and phenylalanine (Phe)-free infant protein-substitute (PS) are gradually replaced with equivalent amounts of Phe-containing food, a semi-solid/spoonable weaning PS and special low-protein foods. In PKU, feeding patterns/practices during weaning in PKU have not been formally evaluated. In this longitudinal, prospective, case-control study (n = 20) infants with PKU transitioning to a second-stage PS, were recruited at weaning (4–6 months) for a comparison of feeding practices and development with non-PKU infants. Subjects were monitored monthly to 12 months and at age 15 months, 18 months and 24 months for: feeding progression; food textures; motor skill development and self-feeding; feeding environment; gastrointestinal symptoms; and negative feeding behaviours. Children with PKU had comparable weaning progression to non-PKU infants including texture acceptance, infant formula volume and self-feeding skills. However, children with PKU had more prolonged Phe-free infant formula bottle-feeding and parental spoon feeding than controls; fewer meals/snacks per day; and experienced more flatulence (p = 0.0005), burping (p = 0.001), retching (p = 0.03); and less regurgitation (p = 0.003). Negative behaviours associated with PS at age 10–18 months, coincided with the age of teething. Use of semi-solid PS in PKU supports normal weaning development/progression but parents require support to manage the complexity of feeding and to normalise the social inclusivity of their child’s family food environment. Further study regarding parental anxiety associated with mealtimes is required.

Development of national consensus statements on food labelling interpretation and protein allocation in a low phenylalanine diet for PKU

BACKGROUND

In the treatment of phenylketonuria (PKU), there was disparity between UK dietitians regarding interpretation of how different foods should be allocated in a low phenylalanine diet (allowed without measurement, not allowed, or allowed as part of phenylalanine exchanges). This led to variable advice being given to patients.

METHODOLOGY

In 2015, British Inherited Metabolic Disease Group (BIMDG) dietitians (n = 70) were sent a multiple-choice questionnaire on the interpretation of protein from food-labels and the allocation of different foods. Based on majority responses, 16 statements were developed. Over 18-months, using Delphi methodology, these statements were systematically reviewed and refined with a facilitator recording discussion until a clear majority was attained for each statement. In Phase 2 and 3 a further 7 statements were added.

RESULTS

The statements incorporated controversial dietary topics including: a practical 'scale' for guiding calculation of protein from food-labels; a general definition for exchange-free foods; and guidance for specific foods. Responses were divided into paediatric and adult groups. Initially, there was majority consensus (≥86%) by paediatric dietitians (n = 29) for 14 of 16 statements; a further 2 structured discussions were required for 2 statements, with a final majority consensus of 72% (n = 26/36) and 64% (n = 16/25). In adult practice, 75% of dietitians agreed with all initial statements for adult patients and 40% advocated separate maternal-PKU guidelines. In Phase 2, 5 of 6 statements were agreed by ≥76% of respondents with one statement requiring a further round of discussion resulting in 2 agreed statements with a consensus of ≥71% by dietitians in both paediatric and adult practice. In Phase 3 one statement was added to elaborate further on an initial statement, and this received 94% acceptance by respondents. Statements were endorsed by the UK National Society for PKU.

CONCLUSIONS

The BIMDG dietitians group have developed consensus dietetic statements that aim to harmonise dietary advice given to patients with PKU across the UK, but monitoring of statement adherence by health professionals and patients is required.

Weaning practices in phenylketonuria vary between health professionals in Europe

Background

In phenylketonuria (PKU), weaning is considered more challenging when compared to feeding healthy infants. The primary aim of weaning is to gradually replace natural protein from breast milk or standard infant formula with solids containing equivalent phenylalanine (Phe). In addition, a Phe-free second stage L-amino acid supplement is usually recommended from around 6 months to replace Phe-free infant formula. Our aim was to assess different weaning approaches used by health professionals across Europe.

Methods

A cross sectional questionnaire (survey monkey®) composed of 31 multiple and single choice questions was sent to European colleagues caring for inherited metabolic disorders (IMD). Centres were grouped into geographical regions for analysis.

Results

Weaning started at 17–26 weeks in 85% (n = 81/95) of centres, >26 weeks in 12% (n = 11/95) and < 17 weeks in 3% (n = 3/95). Infant's showing an interest in solid foods, and their age, were important determinant factors influencing weaning commencement. 51% (n = 48/95) of centres introduced Phe containing foods at 17–26 weeks and 48% (n = 46/95) at >26 weeks. First solids were mainly low Phe vegetables (59%, n = 56/95) and fruit (34%, n = 32/95).

A Phe exchange system to allocate dietary Phe was used by 52% (n = 49/95) of centres predominantly from Northern and Southern Europe and 48% (n = 46/95) calculated most Phe containing food sources (all centres in Eastern Europe and the majority from Germany and Austria). Some centres used a combination of both methods.

A second stage Phe-free L-amino acid supplement containing a higher protein equivalent was introduced by 41% (n = 39/95) of centres at infant age 26–36 weeks (mainly from Germany, Austria, Northern and Eastern Europe) and 37% (n = 35/95) at infant age > 1y mainly from Southern Europe. 53% (n = 50/95) of centres recommended a second stage Phe-free L-amino acid supplement in a spoonable or semi-solid form.

Conclusions

Weaning strategies vary throughout European PKU centres. There is evidence to suggest that different infant weaning strategies may influence longer term adherence to the PKU diet or acceptance of Phe-free L-amino acid supplements; rendering prospective long-term studies important. It is essential to identify an effective weaning strategy that reduces caregiver burden but is associated with acceptable dietary adherence and optimal infant feeding development.