Family conditions and dietary control in phenylketonuria

The Impact of the First 2020 COVID-19 Lockdown on the Metabolic Control of Patients with Phenylketonuria

The present study assessed patients' metabolic control of phenylketonuria (PKU) during the first 2020 COVID-19 lockdown in Poland. Blood (phenylalanine) Phe results of the tests of 535 patients, performed in 2019 and in the first months of 2020, were analysed. The six-week lockdown period was compared to the preceding six-week period as well as to the two corresponding periods of 2019 (three non-lockdown periods). More patients failed to perform Phe tests in the lockdown period (32.7%) than in non-lockdown periods (15.6%, 15.1%, 17.2%; p < 0.001 for all). The median Phe levels for those patients who performed testing in all the four periods did not differ between periods. However, these patients tended to perform only one test during the lockdown (ORs: 1.43 to 1.60; 95% CI: from 1.01-2.04 to 1.11-2.30, p-value 0.02 to 0.005). Patients who did not take blood during the lockdown (46.7%) performed significantly fewer blood tests in the remaining periods (median <IQR>: 1 <0-1> vs. 2 <1-4>; p < 0.001). In conclusion, direct assessment of patients' compliance based upon Phe levels during the pandemic lockdown was not possible. Pre-pandemic non-compliant patients frequently failed to perform the test during the lockdown, whereas the previously compliant ones were more likely to perform only one test. This strongly suggests that metabolic control might have worsened.

Living with phenylketonuria in adulthood: The PKU ATTITUDE study

Dietary treatment is the cornerstone of therapy for phenylketonuria (PKU), but adherence to low- phenylalanine diet progressively decreases after adolescence. We designed a survey to characterize the dietary habits of Italian adult PKU patients and to identify psychological factors influencing disease perception and adherence to diet. Participants to the survey (n = 111; response rate 94%) were asked to complete a structured questionnaire. Patients appeared to have an altered perception and awareness of the disease. About 40% of them did not consider PKU a disease and, despite declaring regular monitoring of phenylalanine levels (85%), nearly half of them reported a high plasma value over the last 6 months (>600 μmol/L, 48%) or were unable to specify it (31%). Adherence to PKU diet was unsatisfactory, with increased consumption of natural protein sources and reduced daily use of amino-acid supplements (<4-5 times/day in 82% patients). In addition to the intrinsic characteristics of AA formula (palatability, ease of use), the most important factor influencing their consumption was the increased social pressure associated with their use (55%). Plasma phenylalanine periodical measurements (61%) and examinations at metabolic centers (49%) were considered relevant for compliance to diet. In Italian adult PKU patients dietary management was found to be inadequate, likely due to inappropriate perception and knowledge of the disease, and lack of awareness of the negative impact of poor metabolic control in adult life. Clinicians should consider implementing more intense and tailored educational measures, as well as structured transitional care processes.

The impact of phenylketonuria on PKU patients' quality of life: Using of the phenylketonuria-quality of life (PKU-QOL) questionnaires

BACKGROUND & AIMS

Phenylketonuria (PKU) has a very high prevalence throughout the world. Nowadays, number of studies about impact of this metabolic disease on patients increasing. The aim of our study is to examine PKU patients' quality of life according to PKU-QOL questionnaires.

METHODS

Patients (n = 63) diagnosed with PKU were included this study; child (9-11 years (n = 20)), adolescent (12-15 years (n = 22)) and adult (18-35 years (n = 21)). PKU-QOL questionnaires (include 4 modules) developed for PKU patients were used. In accordance with purpose, data were analysed by nonparametric tests (Kruskal Wallis One-Way Analysis of Variance Test and Mann-Whitney U Test), according to results of normality tests.

RESULTS

Most of the individuals were female (65,1%) and mean age was 15,7 ± 6,4 years. Symptoms; there were statistically significant differences in all domains excluding tiredness. Especially, median score of slow thinking was very frequent symptom in children as 100,0. PKU in general; there were found that median scores were higher in children. Phe-free amino acid supplement administration: as the age increased, scores were lower. Dietary protein restriction: Overall difficulty following dietary protein restriction and Food enjoyment were found similar in groups (p > 0,05).

CONCLUSIONS

It was concluded that PKU affects younger people more negatively.

[Health and socio-educational needs of the families and children with rare metabolic diseases: Qualitative study in a tertiary hospital]

INTRODUCTION

Rare diseases are a challenge for public health due to the lack of information on their magnitude. These include inborn errors of metabolism. The objective of this study was to assess the quality of life and social, health, economic, and educational needs of a group of paediatric patients with inborn errors of metabolism attended to in a hospital.

MATERIAL AND METHOD

A questionnaire was developed based on the needs and expectations, based mainly on the Andalusian Plan for Rare Diseases. An analysis was performed on the variables of health, socioeconomic, and educational needs of 65 paediatric patients with inborn errors of metabolism.

RESULTS

The respondents showed few possibilities to cope with medication (61%), special diet (86%), and other health benefits (79%). Just under half of them (43%) believed that the quality of family life had been greatly reduced since the onset of the disease. The main caregiver was the mother in 61.5% of cases, compared to 1.5% of cases in which it was the father. The primary caregivers had to reduce their working hours or give up their job in 77% of cases.

CONCLUSIONS

The multidisciplinary treatment is affected by the inability of families to cope with a high cost, as well as with difficult access to these resources. In addition, there is great impact on the quality of life of patients, and their caregivers. Therefore, there is a need to evaluate the results of government health and socio-economic support plans for patients with rare diseases, and make a real response to their needs.

Psychological wellbeing in parents of children with phenylketonuria and association with treatment adherence

BACKGROUND

Phenylketonuria (PKU) is a rare metabolic disorder that leads to severe neurological abnormalities unless early treated with a strict phenylalanine (Phe)-restricted diet. The parents' involvement in PKU management is crucial and could lead to psychological distress; however, few studies have explored the parents' psychological wellbeing. The study aimed to: 1) evaluate the presence of psychological distress and impaired quality of life among parents of children with PKU, assessing the impact of the diagnosis and the impact of the treatment management; 2) explore the associations between parents' psychological outcomes and their children's blood-Phe levels.

METHODS

One hundred thirty-eight parents of patients with PKU (who need a Phe-restricted diet) and with a mild form (mild hyperphenylalaninemia-MHP, with no diet indication) filled-out self-report psychological questionnaires; Phe-levels of children with PKU were retrieved.

RESULTS

Parents of children with PKU did not report higher levels of psychological distress neither compared with the normative scores nor with parents of children with MHP. Optimal Phe-levels were associated with a higher number of parents' depressive complaints, with a lower tendency to express anger feelings, with a lower social functioning, and a higher mental health.

CONCLUSIONS

Parents of children with PKU showed a good psychological adaptation to their children's disease and treatment. Findings highlighted associations between parents' psychological wellbeing and their children's adherence to diet. Interestingly, an optimal adherence to the diet of their children was associated with parental low social functioning, a higher tendency to control the anger expression, and greater somatic depressive symptoms.

Haplotype-based Noninvasive Prenatal Diagnosis of Hyperphenylalaninemia through Targeted Sequencing of Maternal Plasma

Here we developed a haplotype-based noninvasive prenatal diagnosis method for hyperphenylalaninemia (HPA) and demonstrated its accuracy and feasibility during early pregnancy. Capture sequencing was performed on genomic DNA from parents and probands using customized hybridization probes targeting highly heterozygous single-nucleotide polymorphisms located within the 1 M region flanking phenylalanine hydroxylase (PAH) and 6-pyruvoyltetrahydropterin (PTS) and its coding region to determine the parental haplotypes and linkage to pathogenic mutations. Maternal plasma DNA obtained at 12–20 weeks of gestation was also subjected to targeted sequencing to deduce the fetal haplotypes based on the parental haplotypes. The fetal genotypes were further validated by invasive prenatal diagnosis. Haplotype-based noninvasive prenatal testing was successfully performed in 13 families. Five fetuses were identified to harbor bi-allelic pathogenic variants of PAH, four fetuses were carriers of one heterozygous PAH variant, three fetuses were normal, and the fetus of the 6-pyruvoyl tetrahydrobiopterin synthase family was identified as normal. The fetal genotypes at two gestational weeks from the same PAH family were identical. All results were consistent with the prenatal diagnosis based on amniotic fluid. Haplotype-based noninvasive prenatal testing for HPA through targeted sequencing is accurate and feasible during early gestation.

Quality of life and adherence to treatment in early-treated Brazilian phenylketonuria pediatric patients

Early dietary treatment of phenylketonuria (PKU), an inborn error of phenylalanine (Phe) metabolism, results in normal cognitive development. Although health-related quality of life (HRQoL) of PKU patients has been reported as unaffected in high-income countries, there are scarce data concerning HRQoL and adherence to treatment of PKU children and adolescents from Brazil. The present study compared HRQoL scores in core dimensions of Brazilian early-treated PKU pediatric patients with those of a reference population, and explored possible relationships between adherence to treatment and HRQoL. Early-treated PKU pediatric patient HRQoL was evaluated by self- and parent-proxy reports of the Pediatric Quality of Life Inventory (PedsQL) core scales. Adherence to treatment was evaluated by median Phe levels and percentage of results within the therapeutic target range in two periods. Means for total and core scales scores of PedsQL self- and parent proxy-reports of PKU patients were significantly lower than their respective means for controls. Adequacy of median Phe concentrations and the mean percentage of values in the target range fell substantially from the first year of life to the last year of this study. There was no significant difference in mean total and core scale scores for self- and parent proxy-reports between patients with adequate and those with inadequate median Phe concentrations. The harmful consequences for intellectual capacity caused by poor adherence to dietary treatment could explain the observed decrease in all HRQoL scales, especially in school functioning. Healthcare system and financial difficulties may also have influenced negatively all HRQoL dimensions.

Demographic and Psychosocial Influences on Treatment Adherence for Children and Adolescents with PKU: A Systematic Review

Phenylketonuria (PKU) is a rare genetic disorder in which the amino acid phenylalanine cannot be sufficiently metabolised. Although a build-up of phenylalanine causes irreversible cognitive impairment, this can be prevented through a strict, lifelong diet restricted in natural protein. Despite the severe consequences of poor metabolic control, many children and adolescents have phenylalanine levels above their recommended limits. This systematic review was the first to examine studies reporting demographic and/or psychosocial influences on blood phenylalanine levels, with the aim to identify factors that were robustly linked with metabolic control. Four electronic databases were searched, yielding 1,808 articles. Articles were included if they reported a statistical examination of the association between one or more demographic or psychosocial factor(s) and metabolic control (as measured by blood phenylalanine concentration) for children and adolescents with PKU. Twenty-nine studies were selected for inclusion, which examined a range of child, parent and family factors related to blood phenylalanine levels. The most reproducible association was with child age, with metabolic control worsening with increasing age. This suggests that interventions promoting treatment adherence would be particularly beneficial for adolescents. There was a paucity of studies in some areas, and the quality of included studies varied; therefore, the conclusions of this review are preliminary. Research recommendations focus on promoting the growth of the evidence-base to support clinical practice.

Psychological and psychosocial implications for parenting a child with phenylketonuria: a systematic review

INTRODUCTION

Since phenylketonuria (PKU) appears to have specificities that might challenge the parents' adaptation and well-being, the present review aimed to evaluate the impact of parenting a child with PKU on parents' psychological and psychosocial functioning.

EVIDENCE ACQUISITION

A systematic electronic search was conducted using PubMED, Scopus, Embase, PsychInfo, Google Scholar and Cochrane Database to identify studies exploring psychological and psychosocial issues of parents of PKU children. The search retrieved 427 articles to review against inclusion criteria; a total of 17 studies were included in the review. Results were summarized qualitatively.

EVIDENCE SYNTHESIS

Findings revealed a complex pattern of interrelated factors both on parental psychological wellbeing and psychosocial functioning. In particular, crucial for parents' adjustment to child PKU are the diagnosis resolution and the perceived social support; parents showed good coping strategies and quality of life; while, with regard to mental health, the studies reviewed showed inconsistent results, thus pointed out a moderate level of distress. The review examines patterns of results across studies and discusses methodological heterogeneities and problems related to different or inconsistent findings.

CONCLUSIONS

Parenting a child with PKU had direct implications on the diagnosis resolution, the parents mental health and the disease management. Findings could help healthcare professionals to identify situations at risk for psychological maladjustments both in parents and in children, as the unresolved diagnosis or a tendency toward the social isolation. Results highlighted the necessity of a multidisciplinary caring approach for the family, with a particular focus on critical moments such diagnosis or developmental transitions.

Relationships Between Childhood Experiences and Adulthood Outcomes in Women with PKU: A Qualitative Analysis

BACKGROUND

The enduring impact of the childhood experiences of people with phenylketonuria (PKU) on their adulthood outcomes is equivocal. As the effect of childhood experiences on adulthood is well documented amongst the general population, the aim of this study was to explore childhood experiences considered significant by women with PKU as they relate to adult experiences and management of PKU, and psychological wellbeing.

METHOD

Eight women with PKU in South Australia underwent semi-structured interviews. The audio-recorded interviews were transcribed verbatim and analyzed using thematic analysis.

RESULTS

Interviews revealed that feeling different to peers as a child, challenges with management of the condition during adolescence, parental and extended family support, and the perception of PKU as a burden during childhood were associated with adulthood experiences.

CONCLUSIONS

Thus, it is proposed that these childhood factors have a combined, long-term impact. These findings have significant clinical implications, suggesting that early psychosocial intervention relating to these identified childhood experiences has the potential to enhance positive outcomes for adults with PKU.

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/.

Social-cognitive functioning and social skills in patients with early treated phenylketonuria: a PKU-COBESO study

OBJECTIVE

Early treatment of phenylketonuria (ET-PKU) prevents mental retardation, but many patients still show cognitive and mood problems. In this study, it was investigated whether ET-PKU-patients have specific phenylalanine (Phe-)related problems with respect to social-cognitive functioning and social skills.

METHODS

Ninety five PKU-patients (mean age 21.6 ± 10.2 years) and 95 healthy controls (mean age 19.6 ± 8.7 years) were compared on performance of computerized and paper-and-pencil tasks measuring social-cognitive abilities and on parent- and self-reported social skills, using multivariate analyses of variance, and controlling for general cognitive ability (IQ-estimate). Further comparisons were made between patients using tetrahydrobiopterin (BH4, N = 30) and patients not using BH4. Associations with Phe-levels on the day of testing, during childhood, during adolescence and throughout life were examined.

RESULTS

PKU-patients showed poorer social-cognitive functioning and reportedly had poorer social skills than controls (regardless of general cognitive abilities). Quality of social-cognitive functioning was negatively related to recent Phe-levels and Phe-levels between 8 and 12 years for adolescents with PKU. Quality of social skills was negatively related to lifetime phenylalanine levels in adult patients, and specifically to Phe-levels between 0 and 7, and between 8 and 12 years. There were no differences with respect to social outcome measures between the BH4 and non-BH4 groups.

CONCLUSION

PKU-patients have Phe-related difficulties with social-cognitive functioning and social skills. Problems seem to be more evident among adolescents and adults with PKU. High Phe-levels during childhood and early adolescence seem to be of greater influence than current and recent Phe-levels for these patients.

Mutations of the phenylalanine hydroxylase gene in Iranian patients with phenylketonuria

Phenylketonuria (PKU) is an autosomal recessive disease which results from mutations in the phenylalanine hydroxylase (PAH) gene. The aim of this study was the identification of sixteen different mutations in Iranian patients with hyperphenylalaninemia. The mutations were detected during the characterization of PAH genotypes of 39 PKU patients from Qazvin and Zanjan provinces of Iran. PAH mutations have been analyzed by PCR and direct sequencing of PCR products of the promoter region and all 13 exons of PAH gene, including the splicing sites. A mutation detection rate of 74.3 % was realized. Two mutations were found at high frequencies: R176X (10.25 %) and p.P281L (10.25 %). The frequencies of the other mutations were: IVS2+5G>A (2.56 %), IVS2+5G>C (2.56 %), p.L48S (2.56 %), p.R243Q (2.56 %), p.R252Q (5.12 %), p.R261Q (7.69 %), p.R261X (5.12 %), p.E280K (2.56 %), p.I283N (2.56 %), IVS9+5G>A (2.56 %), IVS9+1G>A (1.28 %), IVS11+1G>C (1.28 %), p.C357R (1.28 %), c.632delC (2.56 %). The present results confirm the high heterogeneity of the PAH locus and contribute to information about the distribution and frequency of PKU mutations in the Iranian population.

Access to treatment for phenylketonuria by judicial means in Rio Grande do Sul, Brazil

Treatment of phenylketonuria (PKU) includes the use of a metabolic formula which should be provided free of charge by the Unified Health System (SUS). This retrospective, observational study sought to characterize judicial channels to obtain PKU treatment in Rio Grande do Sul (RS), Brazil. Lawsuits filed between 2001- 2010 and having as beneficiaries PKU patients requesting treatment for the disease were included. Of 20 lawsuits filed, corresponding to 16.8% of RS patients with PKU, 19 were retrieved for analysis. Of these, only two sought to obtain therapies other than metabolic formula. In all the other 17 cases, prior treatment requests had been granted by the State Department of Health. Defendants included the State (n = 19), the Union (n = 1), and municipalities (n = 4). In 18/19 cases, the courts ruled in favor of the plaintiffs. Violation of the right to health and discontinuation of State-provided treatment were the main reasons for judicial recourse. Unlike other genetic diseases, patients with PKU seek legal remedy to obtain a product already covered by the national pharmaceutical assistance policy, suggesting that management failures are a driving factor for judicialization in Brazil.

Newborn screening 50 years later: access issues faced by adults with PKU

Fifty years after the implementation of universal newborn screening programs for phenylketonuria, the first disease identified through newborn screening and considered a success story of newborn screening, a cohort of adults with phenylketonuria treated from birth provides valuable information about effects of long-term treatment for inborn errors of metabolism in general, and phenylketonuria specifically. For phenylketonuria, newborn screening allows early implementation of the phenylalanine-restricted diet, eliminating the severe neurocognitive and neuromotor impairment associated with untreated phenylketonuria. However, executive function impairments and psychiatric problems are frequently reported even for those treated early and continuously with the phenylalanine-restricted diet alone. Moreover, a large percentage of adults with phenylketonuria are reported as lost to follow-up by metabolic clinics. While a group of experts identified by the National Institutes of Health convenes to update treatment guidelines for phenylketonuria, we explore individual patient, social, and economic factors preventing >70% of adult phenylketonuria patients in the United States from accessing treatment. As more conditions are identified through newborn screening, factors affecting access to treatment grow in importance, and we must continue to be vigilant in assessing and addressing factors that affect patient treatment outcomes and not just celebrate amelioration of the most severe manifestations of disease.

Nutrition education tools used in phenylketonuria: clinician, parent and patient perspectives from three international surveys

BACKGROUND

Three international surveys were developed aiming to identify the current nutrition educational tools used in the management of phenylketonuria (PKU) and the perceived effectiveness of these tools by clinicians, parents and patients.

METHODS

The first two surveys were distributed through the Metabolic Dietitians ListServe (pno-metabl@listserv.cc.emory.edu), and the third survey was distributed by international clinics and the National PKU Alliance website (www.npkua.org). A total of 888 responses (S1, n = 88; S2, n = 81; S3, n = 719) were collected from all three surveys. The surveys represent participants from 17 countries, in Europe; North America (USA and Canada); Mexico; Argentina; Turkey; Australia; and Africa (Tunisia).

RESULTS

A consistent decline in 'parents as role models' as an educational tool was observed starting at age 10 years. Patients responded they feel their families are the most effective form of education, whereas handouts were selected as the least effective educational tool by patients. Parents responded they feel the most effective educational tool is one-on-one counselling. Patients and parents show a desirable trend in wanting to attend group clinic, even in centres where this type of educational tool is not offered.

CONCLUSIONS

There was a discrepancy between clinicians and patient views regarding the perceived effectiveness of the nutrition education tools. Future research is needed surrounding the impact nutrition education may have on improved dietary compliance in patients with PKU.

Adherence to diet and quality of life in patients with phenylketonuria

AIM

To investigate adherence to dietary treatment and quality of life (QoL) in patients with phenylketonuria (PKU).

METHODS

In the setting of a tertiary paediatric hospital, 41 early-treated patients affected by PKU aged more than 3 years old were enrolled in a cross-sectional study. Three-days dietary assessment, QoL questionnaires for patients<18 years old (Child Health Questionnaire) and Short Form for adults were completed.

RESULTS

Of 41 patients, 23 (56.1%) were considered adherent to the dietary prescriptions as their phenylalanine intake was less than prescribed. Phenylalanine intake was significantly in excess of prescribed if mothers had a lower level of education. Adherence was not correlated with age. Metabolic control was obtained in 41.5-51.2% of the patients depending on the target. QoL was reduced in children and adolescents. There was no significant correlation between adherence and QoL, except for the domains of Global Health and Family Activities (ρ=0.42 and 0.46, respectively). The overall agreement between adherence and metabolic control varied according to different targets of metabolic control (51.2-65.9%).

CONCLUSIONS

It is necessary to improve the adherence to diet and the QoL in children and adolescents affected by PKU.

Follow up of phenylketonuria patients

In recent years our understanding of the follow up policies for PKU has increased substantially. In particular, we now understand the importance of maintaining control of blood phenylalanine (phe) concentrations life-long to achieve the best long-term neuropsychological outcomes. The concordance with the follow up strategy remains a key challenge for the future, especially with respect to adolescents and young adults. The recent therapies could ease the burden of the dietary phe restriction for PKU patients and their families. The time may be right for revisiting the guidelines for follow up of PKU in order to address a number of important issues related to PKU management: promotion of breastfeeding to complementary feeding up to 2 years of age for prevention of early growth retardation and later overweight development, treatment advancements for metabolic control, blood phe and tyr variability, routine screening measures for nutritional biomarkers, neurocognitive and psychological assessments, bone pathology, understanding the challenges of compliance and transitioning into adulthood as an individual with PKU and addressing unmet needs in this population.

The reality of dietary compliance in the management of phenylketonuria

In phenylketonuria (PKU), it is common for blood phenylalanine (Phe) concentrations to be outside optimal target ranges, particularly in teenagers and adults, indicating inadequate compliance. It is well known that significant noncompliance exists, and the situation in PKU would appear no different than other chronic conditions. In PKU, compliance is complex, being subject to diverse definitions, and factors influencing compliance include the nature and nurture of the patient, as well as the inconvenience, cost and availability of dietary treatment. It is also a dynamic process, with many patients changing between a state of compliance and partial and noncompliance. In PKU, compliance has received little rigorous study, and there have been few observational reports identifying barriers and behaviors impacting dietary compliance. Compliance assessment measures remain inadequately defined. The direct assessment of blood Phe concentration is perhaps the best overall measure, but there is no universal agreement about the number of Phe concentrations that should be within target range and frequency or timing of measurement. Although no one strategy for improving compliance is universally effective, and an individualized approach to noncompliance is essential, it is important to have clear evidence about the most effective strategies in achieving long-term dietary adherence in PKU.

Phenylketonuria

Phenylketonuria is the most prevalent disorder caused by an inborn error in aminoacid metabolism. It results from mutations in the phenylalanine hydroxylase gene. Phenotypes can vary from a very mild increase in blood phenylalanine concentrations to a severe classic phenotype with pronounced hyperphenylalaninaemia, which, if untreated, results in profound and irreversible mental disability. Neonatal screening programmes identify individuals with phenylketonuria. The initiation of a phenylalanine-restricted diet very soon after birth prevents most of the neuropsychological complications. However, the diet is difficult to maintain and compliance is often poor, especially in adolescents, young adults, and pregnant women. Tetrahydrobiopterin stimulates phenylalanine hydroxylase activity in about 20% of patients, and in those patients serves as a useful adjunct to the phenylalanine-restricted diet because it increases phenylalanine tolerance and allows some dietary freedom. Possible future treatments include enzyme substitution with phenylalanine ammonia lyase, which degrades phenylalanine, and gene therapy to restore phenylalanine hydroxylase activity.

Phenylketonuria: outcomes and treatment

Phenylketonuria (PKU) is an inborn error of metabolism affecting approximately one in every 10,000 infants born in Europe and the USA. Unless treated with a phenylalanine-restricted diet beginning in infancy, PKU can be associated with mental retardation, seizures, eczema and other symptoms. Treatment prevents the most severe consequences of PKU, but compliance with the strict dietary regimen is poor, especially in adolescents and adults. Despite the decline in IQ and increased emotional problems associated with poor adherence to the diet, few novel advances in treatments for PKU have occurred since 1963, when it became the first condition for which newborn screening was available. Sparked in part by acceptance of the policy of lifelong dietary treatment, alternative therapies are being investigated. These include innovations in production of low-protein foods, psychosocial interventions, new medications, enzyme therapy and perhaps even gene therapy in the future.