Phenylketonuria in adulthood: a collaborative study

Introduction of sapropterin dihydrochloride as standard of care in patients with phenylketonuria

Sapropterin dihydrochloride, a synthetic, stable form of the tetrahydrobiopterin cofactor of phenylalanine hydroxylase, has been shown to reduce plasma phenylalanine (Phe) levels in a significant portion of patients with phenylketonuria (PKU). When we undertook introducing this medication to our PKU clinic population, the challenges of recalling and reconnecting with a variably treated and variably compliant patient population became apparent. We offered a trial of sapropterin to all of our clinic patients with PKU. In order to determine responsiveness, we used a two tier dose escalation protocol. After diet records were taken, and baseline plasma Phe levels were established, a 7-day trial of sapropterin at 10mg/kg/day was started. At day 8, plasma phenylalanine levels were measured. Patients were considered to be responders if they had a 30% reduction in plasma Phe. If they did not respond, the dose of sapropterin was increased to 20 mg/kg/day, and levels were rechecked again in 8 days. Patients who were not responders at this time continued sapropterin for a total of 30 days and had Phe levels checked one last time. Patients who were responders and who were on a Phe-restricted diet underwent gradual liberalization of their diet to the maximum tolerated natural protein intake while still maintaining plasma levels in the acceptable treatment range of 120-360 micromol/L. In our population, 36/39 patients with hyperphenylalaninemia (HPA) who were offered a trial of sapropterin elected to start sapropterin. Five of 36 patients were non-adherent with diet records and/or medication doses and we were unable to determine if they were responders. We were unable to categorize 2 of 31 of the patients who completed the trial as responders due to dietary issues, though they were probably responders. Of the 29 patients who completed the sapropterin trial and we could categorize, 18/29 (62%) were determined to be responders. Patients were classified based on their off-diet diagnostic plasma phenylalanine levels as classical PKU (>1200 micromol/L) and variant PKU (>400 and <1200 micromol/L). The group with variant PKU had a 100% response rate, and patients with classical PKU had a 27% response rate. For the patients in the responder group who were on Phe-restricted diet, we were able to liberalize most diets, in two cases to unrestricted protein intake. We also had unexpected beneficial findings in our clinic experience, including positive behavioral improvements in an adult severely affected by untreated PKU. Even in patients who were not considered to be responders, the introduction of sapropterin provided a tool to reconnect with patients and re-introduce beneficial dietary measures.

Sapropterin dihydrochloride for phenylketonuria

BACKGROUND

Phenylketonuria results from a deficiency of the enzyme phenylalanine hydroxylase. Dietary restriction of phenylalanine keeps blood phenylalanine concentration low. Most natural foods are excluded from diet and supplements are used to supply other nutrients. Recent publications report a decrease in blood phenylalanine concentration in some patients treated with sapropterin dihydrochloride. We examined the evidence for the use of sapropterin dihydrochloride to treat phenylketonuria.

OBJECTIVES

To assess the safety and efficacy of sapropterin dihydrochloride in lowering blood phenylalanine concentration in people with phenylketonuria.

SEARCH STRATEGY

We identified relevant trials from the Group's Inborn Errors of Metabolism Trials Register. Last search:07 May 2010.We also searched ClinicalTrials.gov and Current controlled trials. Last search: 01 September 2009.We contacted the manufacturers of the drug (BioMarin Pharmaceutical Inc.) for information regarding any unpublished trials.

SELECTION CRITERIA

Randomized controlled trials comparing sapropterin with no supplementation or placebo in people with phenylketonuria due to phenylalanine hydroxylase deficiency.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed trials and extracted outcome data.

MAIN RESULTS

Two placebo-controlled trials were included. One trial administered 10 mg/kg/day sapropterin in 89 children and adults with phenylketonuria whose diets were not restricted and who had previously responded to saproterin.This trial measured change in blood phenylalanine concentration. The second trial screened 90 children (4 to 12 years) with phenylketonuria whose diet was restricted, for responsiveness to sapropterin. Forty-six responders entered the placebo-controlled part of the trial and received 20 mg/kg/day sapropterin. This trial measured change in both phenylalanine concentration and protein tolerance. Both trials reported adverse events. The trials showed an overall low risk of bias; but both are Biomarin-sponsored. One trial showed a significant lowering in blood phenylalanine concentration in the sapropterin group (10 mg/kg/day), mean difference -238.80 mumol/L (95% confidence interval -343.09 to -134.51); a second trial (20 mg/kg/day sapropterin) showed a non-significant difference, mean difference -51.90 mumol/L (95% confidence interval -197.27 to 93.47). The second trial also reported a significant increase in phenylalanine tolerance, mean difference18.00 mg/kg/day (95% confidence interval 12.28 to 23.72) in the 20 mg/kg/day sapropterin group.

AUTHORS' CONCLUSIONS

There is evidence of short-term benefit from using sapropterin in some patients with sapropterin-responsive forms of phenylketonuria; blood phenylalanine concentration is lowered and protein tolerance increased. There are no serious adverse events associated with using sapropterin in the short term.There is no evidence on the long-term effects of sapropterin and no clear evidence of effectiveness in severe phenylketonuria.

Phenylketonuria management from an European perspective: a commentary

Phenylketonuria is discussed from an European perspective, addressing the need of common definitions of terms commonly used, the need of a world-wide guideline on the diagnosis and treatment of phenylketonuria, the differences between existing European guidelines, and day-to-day care, further directives for the near future, and changing the concept from compliance to concordance, in which patients have a more clearly defined responsibility.

Comparison of adeno-associated virus pseudotype 1, 2, and 8 vectors administered by intramuscular injection in the treatment of murine phenylketonuria

Phenylketonuria (PKU) is caused by hepatic phenylalanine hydroxylase (PAH) deficiency and is associated with systemic accumulation of phenylalanine (Phe). Previously we demonstrated correction of murine PKU after intravenous injection of a recombinant type 2 adeno-associated viral vector pseudotyped with type 8 capsid (rAAV2/8), which successfully directed hepatic transduction and Pah gene expression. Here, we report that liver PAH activity and phenylalanine clearance were also restored in PAH-deficient mice after simple intramuscular injection of either AAV2 pseudotype 1 (rAAV2/1) or rAAV2/8 vectors. Serotype 2 AAV vector (rAAV2/2) was also investigated, but long-term phenylalanine clearance has been observed only for pseudotypes 1 and 8. Therapeutic correction was shown in both male and female mice, albeit more effectively in males, in which correction lasted for the entire period of the experiment (>1 year). Although phenylalanine levels began to rise in female mice at about 8-10 months after rAAV2/8 injection they remained only mildly hyperphenylalaninemic thereafter and subsequent supplementation with synthetic tetrahydrobiopterin resulted in a transient decrease in blood phenylalanine. Alternatively, subsequent administration of a second vector with a different AAV pseudotype to avoid immunity against the previously administrated vector was also successful for long-term treatment of female PKU mice. Overall, this relatively less invasive gene transfer approach completes our previous studies and allows comparison of complementary strategies in the development of efficient PKU gene therapy protocols.

Dietary interventions for phenylketonuria

BACKGROUND

Phenylketonuria is an inherited disease treated with dietary restriction of the amino acid phenylalanine. The diet is initiated in the neonatal period to prevent mental handicap; however, it is restrictive and can be difficult to follow. Whether the diet can be relaxed or discontinued during adolescence or should be continued for life remains a controversial issue, which we aim to address in this review.

OBJECTIVES

To assess the effects of a low-phenylalanine diet commenced early in life for people with phenylketonuria. To assess the possible effects of relaxation or termination of the diet on intelligence, neuropsychological outcomes and mortality, growth, nutritional status, eating behaviour and quality of life.

SEARCH STRATEGY

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group Trials Register comprising references identified from comprehensive electronic database searches, handsearches of relevant journals and abstract books of conference proceedings.Most recent search of the Inborn Errors of Metabolism Trials Register: 05 March 2009.

SELECTION CRITERIA

All randomised or quasi-randomised controlled trials comparing a low-phenylalanine diet to relaxation or termination of dietary restrictions in people with phenylketonuria.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed study eligibility and methodological quality, and subsequently extracted the data.

MAIN RESULTS

We included four studies in this review (251 participants), and found few significant differences between treatment and comparison groups for the outcomes of interest. Blood phenylalanine levels were significantly lower in participants with phenylketonuria following a low-phenylalanine diet compared to those on a less restricted diet, mean difference (MD) at three months -698.67 (95% confidence interval (CI) -869.44 to -527.89). Intelligence quotient was significantly higher in participants who continued the diet than in those who stopped the diet, MD after 12 months 5.00 (95% CI 0.40 to 9.60). However, these results came from a single study.

AUTHORS' CONCLUSIONS

The results of non-randomised studies have concluded that a low-phenylalanine diet is effective in reducing blood phenylalanine levels and improving intelligence quotient and neuropsychological outcomes. We were unable to find any randomised controlled studies that have assessed the effect of a low-phenylalanine diet versus no diet from diagnosis. In view of evidence from non-randomised studies, such a study would be unethical and it is recommended that low-phenylalanine diet should be commenced at the time of diagnosis. There is uncertainty about the precise level of phenylalanine restriction and when, if ever, the diet should be relaxed. This should be addressed by randomised controlled studies.

Reassessment of phenylalanine tolerance in adults with phenylketonuria is needed as body mass changes

Lifelong treatment of phenylketonuria (PKU) includes a phenylalanine (phe) restricted diet that provides sufficient phe for growth and maintenance plus phe-free amino acid formula to meet requirements for protein, energy and micronutrients. Phe tolerance (mg phe/kg body weight/day) is the amount of phe those with PKU can consume and maintain acceptable blood phe levels; it requires individual assessment because of varying phenylalanine hydroxylase activity. The objective was to reassess phe tolerance in eight adults with PKU considering phe requirements, blood phe levels, genotype and phe tolerance at 5 years of age. Subjects had not received a personalized assessment of phe tolerance in several years, and five subjects were overweight, body mass index (BMI) 25-28. With the guidance of a metabolic dietitian, seven subjects increased phe tolerance (by 15-173%) without significantly increasing blood phe concentration. Increased phe tolerance was associated with both improved dietary compliance and inadequate phe intake at the onset of the protocol compared with current requirements. Improved dietary compliance reflected increased consumption of protein equivalents from amino acid formula and increased frequency of formula intake, from 2.2 to 3 times per day. Predictors of higher final phe tolerance following reassessment included being male and having a lower BMI (R(2)=0.588). This suggests that the rising trend of overweight and obesity may affect assessment of phe tolerance in adults. Therefore, interaction with the metabolic dietitian to reassess phe tolerance in relation to body mass is essential throughout adulthood to insure adequate intake of phe to support protein synthesis and prevent catabolism.

Recent Advances in Pharmacotherapy

Many unique and clinically important medications were approved by the Food and Drug Administration from December 2007 through May 2008 for various conditions encountered in an internal medicine setting. These new treatments dramatically vary in their targeted body system and include agents for the cardiovascular system (nebivolol), central nervous system (desvenlafaxine), gastrointestinal tract (certolizumab, methylnaltrexone, and alvimopan), immunological function (etravirine), and metabolic function (sapropterin). This article discusses medications by their respective body system. Each review is comprised of an overview of the Food and Drug Administration–approved indication and the drug’s role in treatment of that disease state. Current dosing guidance, clinical efficacy and clinically relevant adverse drug reactions, drug interactions, contraindications, and precautions are also presented. This review is designed to focus on the new molecular entities and biological approvals clinicians may potentially encounter in an internal medicine practice.

Sapropterin: a new therapeutic agent for phenylketonuria

OBJECTIVE

To summarize the role of pharmacotherapy in the management of phenylketonuria (PKU) and to review the pharmacology, pharmacokinetics, pharmacodynamics, efficacy data, and safety profile of sapropterin for this indication.

DATA SOURCES

A literature search was conducted using MEDLINE (1966-May 2009), International Pharmaceutical Abstracts (1970-May 2009), and Cochrane database (2008) for the following key words: sapropterin, tetrahydrobiopterin, phenylketonurias, and phenylalanine.

STUDY SELECTION AND DATA EXTRACTION

English-language studies involving humans examining the role of tetrahydrobiopterin (BH4) in the management of PKU were reviewed to evaluate the pharmacology, pharmacokinetics, pharmacodynamics, efficacy data, and safety profile for sapropterin. All Phase 2 and 3 randomized controlled trials assessing the safety and efficacy of sapropterin were included in this literature evaluation.

DATA SYNTHESIS

Sapropterin represents the only Food and Drug Administration-approved medication for BH4-responsive PKU, marking an important advance in the treatment of this condition. Among individuals with hyperphenylalaninemia and some residual phenylalanine hydroxylase function, sapropterin can enhance activity of this enzyme to decrease serum phenylalanine concentrations. Sapropterin has been compared with placebo in one Phase 2 and one Phase 3 clinical trial, demonstrating significantly better response rates. Based on available studies, this agent appears to be safe and well tolerated, with adverse event rates similar to those of placebo. However, additional studies are warranted to assess the long-term safety and efficacy of sapropterin therapy.

CONCLUSIONS

Sapropterin offers a promising therapeutic option for select individuals with BH4-responsive PKU, although long-term data are limited evaluating its safety and efficacy in traditional clinical practice settings. When considering sapropterin therapy, clinicians must consider factors such as cost and patient adherence to drug therapy and/or diet.

A limited spectrum of phenylalanine hydroxylase mutations is observed in phenylketonuria patients in western Poland and implications for treatment with 6R tetrahydrobiopterin

Phenylketonuria (PKU) is an autosomal recessive defect in hepatic metabolism of phenylalanine, which is secondary to mutations in the phenylalanine hydroxylase (PAH) gene. Sixty-seven ethnically Polish PKU patients, followed at the Outpatient Department of Pediatrics and Developmental Medicine in Poznan, Poland, were assessed for mutations in the PAH gene. Two mutations were identified in 61 of 67 patients and a single mutation was identified in the remaining six patients. The four most prevalent mutations (p.R408W, 68%; c.1066-11G>A, 6%; c.1315+1G>A, 5.2%; c.822-832delGCCCATGTATA, 3.7%) accounted for 83% of the mutant alleles. Fifteen additional mutations were identified of which most (13/15) were observed in an individual patient. Before knowledge of PAH genotypes, 19 patients were challenged with a 20 mg kg(-1) dose of 6R tetrahydrobiopterin (BH(4)) and serum phenylalanine concentration was monitored in hospital over 24 h. Two patients responded to the BH(4) challenge with a reduction of serum phenylalanine concentration >30% from baseline. PAH genotypes of the two responsive patients would have been predicted, as they contained mutations recognized as BH(4) responsive, whereas the 17 patients who were unresponsive would have been predicted as their mutations were either recognized as non-responsive or were highly deleterious frame-shift mutations. Overall, only 7.5% (5/ 67) of patients had PAH mutations recognized as responsive to co-factor therapy. Among the PKU patients from western Poland, PAH mutations responsive to BH(4) therapy are poorly represented; therefore, genotyping may be useful for identifying candidate patients likely to respond to BH(4) before physiological challenge.

Improved nutritional management of phenylketonuria by using a diet containing glycomacropeptide compared with amino acids

BACKGROUND

Phenylketonuria (PKU) requires a lifelong low-phenylalanine diet that provides the majority of protein from a phenylalanine-free amino acid (AA) formula. Glycomacropeptide (GMP), an intact protein formed during cheese production, contains minimal phenylalanine.

OBJECTIVE

The objective was to investigate the effects of substituting GMP food products for the AA formula on acceptability, safety, plasma AA concentrations, and measures of protein utilization in subjects with PKU.

DESIGN

Eleven subjects participated in an inpatient metabolic study with two 4-d treatments: a current AA diet (AA diet) followed by a diet that replaced the AA formula with GMP (GMP diet) supplemented with limiting AAs. Plasma concentrations of AAs, blood chemistries, and insulin were measured and compared in AA (day 4) and GMP diets (day 8).

RESULTS

The GMP diet was preferred to the AA diet in 10 of 11 subjects with PKU, and there were no adverse reactions to GMP. There was no significant difference in phenylalanine concentration in postprandial plasma with the GMP diet compared with the AA diet. When comparing fasting with postprandial plasma, plasma phenalyalanine concentration increased significantly with the AA but not with the GMP diet. Blood urea nitrogen was significantly lower, which suggests decreased ureagenesis, and plasma insulin was higher with the GMP diet than with the AA diet.

CONCLUSIONS

GMP, when supplemented with limiting AAs, is a safe and highly acceptable alternative to synthetic AAs as the primary protein source in the nutritional management of PKU. As an intact protein source, GMP improves protein retention and phenylalanine utilization compared with AAs.

Biochemical characterization of mutant phenylalanine hydroxylase enzymes and correlation with clinical presentation in hyperphenylalaninaemic patients

The biochemical properties of mutant phenylalanine hydroxylase (PAH) enzymes and clinical characteristics of hyperphenylalaninaemic patients who bear these mutant enzymes were investigated. Biochemical characterization of mutant PAH enzymes p.D143G, p.R155H, p.L348V, p.R408W and p.P416Q included determination of specific activity, substrate activation, V(max), K(m) for (6R)-L-erythro-5,6,7,8-tetrahydrobiopterin (BH(4)), K (d) for BH(4), and protein stabilization by BH(4). Clinical data from 22 patients either homozygous, functionally hemizygous, or compound heterozygous for the mutant enzymes of interest were correlated with biochemical parameters of the mutant enzymes. The p.L348V and p.P416Q enzymes retain significant catalytic activity yet were observed in classic and moderate PKU patients. Biochemical studies demonstrated that BH(4) rectified the stability defects in p.L348V and p.P416Q; additionally, patients with these variants responded to BH(4) therapy. The p.R155H mutant displayed low PAH activity and decreased apparent affinity for L-Phe yet was observed in mild hyperphenylalaninaemia. The p.R155H mutant does not display kinetic instability, as it is stabilized by BH(4) similarly to wild-type PAH; thus the residual activity is available under physiological conditions. The p.R408W enzyme is dysfunctional in nearly all biochemical parameters, as evidenced by disease severity in homozygous and hemizygous patients. Biochemical assessment of mutant PAH proteins, especially parameters involving interaction with BH(4) that impact protein folding, appear useful in clinical correlation. As additional patients and mutant proteins are assessed, the utility of this approach will become apparent.

Phenylketonuria in Children and Mothers: Genes, Environments, Behavior

Phenylketonuria (PKU) is an inborn metabolic error in which metabolism of phenylalanine into tyrosine is disrupted. If the diet of an infant with PKU is not restricted, blood phenylalanine levels are elevated, leading to irremediable brain damage and severe mental retardation. Children with PKU who are placed early and continuously on a low-phenylalanine diet develop normal levels of intelligence, and brain damage is largely prevented. However, if the diet of a mother with PKU is unrestricted during her pregnancy, high phenylalanine levels in her blood can cross the placental barrier and damage the developing fetus in multiple ways. These results demonstrate how genes and environmental factors combine to create prenatal environments that can have profound effects on the growth and development of offspring during infancy and childhood.

Nutritional management of PKU with glycomacropeptide from cheese whey

Individuals with phenylketonuria (PKU) must follow a lifelong low-phenylalanine (Phe) diet to prevent neurological impairment. Compliance with the low-Phe diet is often poor owing to restriction in natural foods and the requirement for consumption of a Phe-free amino acid formula or medical food. Glycomacropeptide (GMP), a natural protein produced during cheese-making, is uniquely suited to a low-Phe diet because when isolated from cheese whey it contains minimal Phe (2.5-5 mg Phe/g protein). This paper reviews progress in evaluating the safety, acceptability and efficacy of GMP in the nutritional management of PKU. A variety of foods and beverages can be made with GMP to improve the taste, variety and convenience of the PKU diet. Sensory studies in individuals with PKU demonstrate that GMP foods are acceptable alternatives to amino acid medical foods. Studies in the PKU mouse model demonstrate that GMP supplemented with limiting indispensable amino acids provides a nutritionally adequate source of protein and improves the metabolic phenotype by reducing concentrations of Phe in plasma and brain. A case report in an adult with classical PKU who followed the GMP diet for 10 weeks at home indicates safety, acceptability of GMP food products, a 13-14% reduction in blood Phe levels (p<0.05) and improved distribution of dietary protein throughout the day compared with the amino acid diet. In summary, food products made with GMP that is supplemented with limiting indispensable amino acids provide a palatable alternative source of protein that may improve dietary compliance and metabolic control of PKU.

The truth of treating patients with phenylketonuria after childhood: the need for a new guideline

In recent years, an increasing number of national guidelines on the treatment of phenylketonuria (PKU) have emerged. Most of these guidelines are dedicated to the care of children, while less attention is paid to the care of adults, although all guidelines underline the importance of diet for life. This review aims to summarize issues that need to be addressed within a guideline on the treatment of PKU, especially when care for patients beyond childhood is concerned. In this respect, it is of importance that adult patients, both willing and unwilling to be treated, need a guideline for care and follow-up. In PKU there is certainly a need for an improved unified guideline, especially after childhood, although many of the considerations in this article also apply to recommendations for treatment of children. Such a guideline will be a tool to improve treatment in PKU patients but should also include recommendations for collecting data for clinical and research purposes. Guideline development should also focus on nutritional, neuropsychological and psychosocial issues and not only on target plasma phenylalanine concentrations. In addition, guidelines must address not only what has to be done but also how it can be done, thereby improving concordance with the recommendations for treatment and management.

Altered brain gene expression profiles associated with the pathogenesis of phenylketonuria in a mouse model

BACKGROUND

Phenylketonuria (PKU) is an autosomal recessive disorder caused by a deficiency of phenylalanine hydroxylase (PAH), which catalyzes the conversion of phenylalanine to tyrosine. The resultant hyperphenylalaninemia causes mental retardation, seizure, and abnormalities in behavior and movement.

METHODS

We analyzed gene expression profiles in brain tissues of Pah(enu2) mice to elucidate the mechanisms involved in phenylalanine-induced neurological damage. The altered gene expression was confirmed by real-time PCR and Western blotting. To identify markers associated with neurological damage, we examined TTR expression in serum by Western blotting.

RESULTS

Gene expression profiling of brain tissue from a mouse model of PKU revealed overexpression of transthyretin (Ttr), sclerostin domain containing 1 (Sostdc1), alpha-Klotho (Kl), prolactin receptor (Prlr), and early growth response 2 (Egr2). In contrast to its overexpression in the brain, TTR expression was low in the sera of PKU mice offered unrestricted access to a diet containing phenylalanine. Expression of TTR decreased in a time-dependent manner in phenylalanine-treated HepG2 cells.

CONCLUSIONS

These findings indicate that Ttr, Sostdc1, Kl, Prlr, and Egr2 can be involved in the pathogenesis of PKU and that phenylalanine might have a direct effect on the level of TTR in serum.

Regulation of M2-type pyruvate kinase mediated by the high-affinity IgE receptors is required for mast cell degranulation

BACKGROUND AND PURPOSE

M2-type pyruvate kinase (M2PK) was found to interact directly with the 'ITAM' region of the gamma chain of the high-affinity IgE receptor (FcvarepsilonRI). Our hypothesis was that mast cell degranulation might require the FcvarepsilonRI-mediated inhibition of M2PK activity.

EXPERIMENTAL APPROACH

In rat basophilic leukaemia (RBL-2H3) cells, the effects of directly inhibiting M2PK or preventing the FcvarepsilonRI-mediated inhibition of M2PK (disinhibition) on degranulation was measured by hexosaminidase release. Effects of blocking the FcvarepsilonRI-mediated inhibition of M2PK was also assessed in vivo in a mouse model of allergen-induced airway hyper-responsiveness.

KEY RESULTS

Activation of FcvarepsilonRI in RBL-2H3 cells caused the rapid phosphorylation of tyrosine residues in M2PK, associated with a decrease in M2PK enzymatic activity. There was an inverse correlation between M2PK activity and mast cell degranulation. FcvarepsilonRI-mediated inhibition of M2PK involved Src kinase, phosphatidylinositol 3-kinase, PKC and calcium. Direct inhibition of M2PK potentiated FcvarepsilonRI-mediated degranulation and prevention of the FcvarepsilonRI-mediated inhibition of M2PK attenuated mast cell degranulation. Transfection of RBL-2H3 cells with M1PK which prevents FcvarepsilonRI-induced inhibition of M2PK, markedly reduced their degranulation and exogenous M1PK (i.p.) inhibited ovalbumin-induced airway hyper-responsiveness in vivo.

CONCLUSIONS AND IMPLICATIONS

We have identified a new control point and a novel biochemical pathway in the process of mast cell degranulation. Our study suggests that the FcvarepsilonRI-mediated inhibition of M2PK is a crucial step in responses to allergens. Moreover, the manipulation of glycolytic processes and intermediates could provide novel strategies for the treatment of allergic diseases.

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.

Evaluation of quality of life and description of the sociodemographic state in adolescent and young adult patients with phenylketonuria (PKU)

BACKGROUND

Normal intellectual and personal development can be expected in early-diagnosed and treated PKU patients. Aim of the study was to analyse quality of life and social status, which are important parameters for an overall estimation of success of treatment apart from intellectual outcome in adult PKU patients.

METHODS

67 patients completed a questionnaire on quality of life and social status. Data was compared to the German census on an age matched control collective.

RESULTS

Quality of life measured with the Profile of Quality of Life in the Chronically Ill (PLC) revealed mean values for capacity of performance in the patient group in the same range as in the control collective. The analysis of the social state of PKU patients revealed a tendency towards lower or delayed autonomy, and a low rate of forming normal adult relationships in which to have children. Schooling and professional career corresponded approximately to the control collective.

CONCLUSION

Though every chronic disorder must be regarded as restraining, it shows that PKU does not preclude healthy emotional adjustment when the disease is diagnosed early and treated well.

Dietary glycomacropeptide supports growth and reduces the concentrations of phenylalanine in plasma and brain in a murine model of phenylketonuria

Phenylketonuria (PKU) is a genetic disorder caused by deficiency of phenylalanine hydroxylase (PAH) that requires life-long adherence to a low-phenylalanine (Phe) diet. Glycomacropeptide (GMP) is uniquely suited to the nutritional management of PKU, because pure GMP contains no Phe. Our aim was to assess how ingestion of diets containing GMP support growth and affect the concentrations of amino acids in plasma and brains of mice with a deficiency of PAH, the Pah(enu2) mouse (PKU mouse). Experiments were conducted in 4- to 6-wk-old wild-type (WT) (C57Bl/6) and PKU mice fed diets containing 20% protein from casein, amino acids, or GMP supplemented with limiting indispensable amino acids (IAA). PKU mice fed the GMP diet showed gains in body weight, feed efficiency, and a protein efficiency ratio that did not differ from the amino acid diet. The concentrations of isoleucine and threonine in plasma showed a significant 2- to 3-fold increase for WT and PKU mice fed GMP compared with casein or amino acid diets, respectively. PKU mice fed the GMP diet had decreased concentrations of Phe in plasma (11% decrease) and in 5 regions of the brain (20% decrease) compared with the amino acid diet. The concentration of Phe in the brain was inversely correlated with the concentrations of isoleucine, threonine, and valine in plasma (R2 = 0.74; P < 0.0001), suggesting competitive inhibition of Phe transport into the brain. In summary, PKU mice fed GMP showed comparable growth and reduced concentrations of Phe in plasma and the brain compared with an amino acid diet. These data support the use of GMP supplemented with IAA as an alternative source of dietary protein for individuals with PKU.

Acceptable low-phenylalanine foods and beverages can be made with glycomacropeptide from cheese whey for individuals with PKU

Glycomacropeptide (GMP) is a whey protein that contains no aromatic amino acids including phenylalanine (phe). The objective of this study was to make a variety of palatable, low-phe foods and beverages with GMP and to assess their acceptability by conducting consumer sensory studies in individuals with PKU. Results demonstrate acceptability of products made with GMP. GMP supplemented with limiting indispensable amino acids could provide an alternative protein source for individuals with PKU.

Phenylalanine blood levels and clinical outcomes in phenylketonuria: a systematic literature review and meta-analysis

Blood phenylalanine (Phe) levels provide a practical and reliable method for the diagnosis and monitoring of metabolic status in patients with phenylketonuria (PKU). To assess the reliability of blood Phe levels as a predictive biomarker of clinical outcomes in the development of treatments for PKU, a systematic literature review and meta-analysis of published trials of PKU, which included Phe level and neurological and dietary compliance outcome measures, was conducted. Within-study correlations between Phe level and intelligence quotient (IQ) were extracted from 40 studies. Significant, proportional correlations were found during critical periods (from 0 to 12 years of age) for early-treated patients with PKU (r=-0.35; 95% confidence interval [CI]: -0.44 to -0.27), where each 100 micromol/l increase in Phe predicted a 1.3- to 3.1-point reduction in IQ. Similar significant correlations were observed between IQ and mean lifetime Phe level for early-treated patients (r=0.34; 95% CI: -0.42 to -0.25), where each 100 micromol/l increase in Phe predicted a 1.9- to 4.1-point reduction in IQ. Moderate correlations were found between concurrent Phe level and IQ for early-treated patients. In conclusion, these results confirm a significant correlation between blood Phe level and IQ in patients with PKU, and support the use of Phe as a predictive biomarker for IQ in clinical trials.

Efficacy of sapropterin dihydrochloride (tetrahydrobiopterin, 6R-BH4) for reduction of phenylalanine concentration in patients with phenylketonuria: a phase III randomised placebo-controlled study

BACKGROUND

Early and strict dietary management of phenylketonuria is the only option to prevent mental retardation. We aimed to test the efficacy of sapropterin, a synthetic form of tetrahydrobiopterin (BH4), for reduction of blood phenylalanine concentration.

METHODS

We enrolled 89 patients with phenylketonuria in a Phase III, multicentre, randomised, double-blind, placebo-controlled trial. We randomly assigned 42 patients to receive oral doses of sapropterin (10 mg/kg) and 47 patients to receive placebo, once daily for 6 weeks. The primary endpoint was mean change from baseline in concentration of phenylalanine in blood after 6 weeks. Analysis was on an intention-to-treat basis. The study is registered with ClinicalTrials.gov, number NCT00104247.

FINDINGS

88 of 89 enrolled patients received at least one dose of study drug, and 87 attended the week 6 visit. Mean age was 20 (SD 9.7) years. At baseline, mean concentration of phenylalanine in blood was 843 (300) micromol/L in patients assigned to receive sapropterin, and 888 (323) micromol/L in controls. After 6 weeks of treatment, patients given sapropterin had a decrease in mean blood phenylalanine of 236 (257) micromol/L, compared with a 3 (240) micromol/L increase in the placebo group (p<0.0001). After 6 weeks, 18/41 (44%) patients (95% CI 28-60) in the sapropterin group and 4/47 (9%) controls (95% CI 2-20) had a reduction in blood phenylalanine concentration of 30% or greater from baseline. Blood phenylalanine concentrations fell by about 200 micromol/L after 1 week in the sapropterin group and this reduction persisted for the remaining 5 weeks of the study (p<0.0001). 11/47 (23%) patients in the sapropterin group and 8/41 (20%) in the placebo group experienced adverse events that might have been drug-related (p=0.80). Upper respiratory tract infections were the most common disorder.

INTERPRETATION

In some patients with phenylketonuria who are responsive to BH4, sapropterin treatment to reduce blood phenylalanine could be used as an adjunct to a restrictive low-phenylalanine diet, and might even replace the diet in some instances.

A neuropsychological profile of off-diet adults with phenylketonuria

The metabolic disorder phenylketonuria (PKU) is treated early by a low-phenylalanine diet. While this prevents global cognitive impairment, some patients still experience cognitive and neurophysiological abnormalities. Neuropsychological testing of early treated, currently off-diet, PKU patients attending an adult PKU clinic showed a reduction in the Perceptual Organization Index (POI), Processing Speed Index (PSI) from the Wechsler Adult Intelligence Scale Third Edition (WAIS-III), and Part A of the Trail Making Test for the PKU group relative to controls. Taken together, these results supported a profile of reduced information-processing speed.

Meta-Analysis of Neuropsychological Symptoms of Adolescents and Adults with PKU

Phenylketonuria (PKU; OMIM 261600) is an autosomal recessive inborn error of phenylanaline metabolism. PKU is characterized by deficient or defective phenylalanine hydroxylase activity and persistantly increased levels of the essential amino acid phenylalanine in the circulation. The present article examines current understanding of the etiology of PKU, along with a meta-analysis examining neuropsychological and intellectual presentations in continuously treated adolescents and adults. Patients with PKU differed significantly from controls on Full-Scale IQ, processing speed, attention, inhibition, and motor control. Future research utilizing an integrative approach and detailed analysis of specific cognitive domains will assist both the scientist and clinician, and ultimately the patient.

The cost-effectiveness of expanding newborn screening for up to 21 inherited metabolic disorders using tandem mass spectrometry: results from a decision-analytic model

OBJECTIVES

In 2005, in Ontario, Canada, newborns were only screened for phenylketonuria (PKU) and hypothyroidism. Tandem mass spectrometry (MS/MS) has since been implemented as a new screening technology because it can screen for PKU and many other diseases simultaneously. We estimated the cost-effectiveness of using this technology to expand the Ontario newborn screening program to screen for each disease independently and for hypothetical bundles of up to 21 metabolic diseases.

METHODS

We constructed a decision-analytic model to estimate the incremental costs and life-years of survival that can be gained by screening or changing screening technologies. Costs and health benefits were estimated for a cohort of babies born in Ontario in 1 year. Secondary sources and expert opinion were used to estimate the test characteristics, disease prevalence, treatment effectiveness, disease progression rates, and mortality. The London Health Sciences Centre Case Costing Initiative, the Ontario Health Insurance Plan Schedule, and the Ontario Drug Benefits plan formulary were used to estimate costs.

RESULTS

Changing screening technologies, from the Guthrie test to MS/MS, for PKU detection had an incremental cost of $5,500,000 per life-year (LY) gained. We identified no diseases for which the incremental cost of screening for just that disease was less than $100,000 per LY gained. The incremental costs of screening ranged from $222,000 (HMG-CoA lyase deficiency) to $142,500,000 (glutaric acidemia type II) per LY gained. Screening for a bundle of diseases including PKU and the 14 most cost-effective diseases to screen for cost less than $70,000 per LY gained, and the incremental cost-effectiveness of adding each of the 14 diseases to the bundle was less than $100,000 per LY gained. The incremental cost of adding the 15th most cost-effective disease was $309,400 per LY gained.

CONCLUSIONS

Early diagnosis and treatment of metabolic disease is important to reduce disease severity and delay or prevent the onset of the disease. Screening at birth reduces the morbidity, mortality, and social burden associated with the irreversible effects of disease on the population. Our analysis suggests that the cost-efficiencies gained by using MS/MS to screen for bundles of diseases rather than just one disease are sufficient to warrant consideration of an expanded screening program. It is, however, not cost-effective to screen for all diseases that can be screened for using this technology.

The course of life and quality of life of early and continuously treated Dutch patients with phenylketonuria

Phenylketonuria (PKU; OMIM 261600) is an autosomal recessive disorder of phenylalanine metabolism caused by a deficiency of the enzyme phenylalanine hydroxylase (PAH; EC 1.14.16.1). Cognitive problems, neuropsychological abnormalities and psychosocial problems have been reported frequently in children and adolescents with PKU, even in those who are treated early and continuously. However, the developmental consequences in adulthood of growing up with PKU are not well known. The aim of this study was to assess the course of life, sociodemographic outcomes and health-related quality of life in young adult patients with PKU identified on neonatal screening who were continuously on treatment. A total of 32 PKU patients 18 to 30 years old completed the Course of Life questionnaire, the RAND-36 Health Survey, and the cognitive scale of the TNO-AZL Adult Quality of Life (TAAQoL) questionnaire. The results of the Course of Life and Health-Related Quality of Life questionnaires were comparable to controls, except that a higher percentage received special education in primary school. Their educational attainment, however, was comparable to that of their peers. The results of this study demonstrate that although PKU is a chronic disease with the burden of strict dietary control, early and continuously treated patients with PKU can have a normal health-related quality of life and course of life.

Event-related potentials elicited during a visual Go-Nogo task in adults with phenylketonuria

OBJECTIVE

The aim of the present study was to examine the nature of previously reported deficits in sustained attention and response inhibition in adults with the developmental disorder, phenylketonuria (PKU).

METHODS

This study used event-related potentials (ERPs) to examine the performance of PKU adults (n=9) and a matched control group (n=9) on a visual Go-Nogo task.

RESULTS

Comparison of behavioural measures between the PKU and control groups failed to reach statistical significance, yet analysis of the ERPs showed statistically significant amplitude reductions in the P1 and N1 components elicited following presentation of stimuli, and a reduction in the amplitude of the N2 component elicited following presentation of Nogo stimuli.

CONCLUSIONS

These results suggest that adults with PKU, despite being continuously treated from birth, manifest subtle impairments in distinct aspects of information processing including early sensory processing of visually presented information, as well as impairments in inhibitory functions.

SIGNIFICANCE

The results contribute to an understanding of the neurophysiological mechanisms that are implicated in PKU and highlight the sensitivity of ERP techniques for the identification of the loci of information processing deficits in clinical groups.

Administration-route and gender-independent long-term therapeutic correction of phenylketonuria (PKU) in a mouse model by recombinant adeno-associated virus 8 pseudotyped vector-mediated gene transfer

Phenylketonuria (PKU) is an inborn error of metabolism caused by deficiency of the hepatic enzyme phenylalanine hydroxylase (PAH) which leads to high blood phenylalanine (Phe) levels and consequent damage of the developing brain with severe mental retardation if left untreated in early infancy. The current dietary Phe restriction treatment has certain clinical limitations. To explore a long-term nondietary restriction treatment, a somatic gene transfer approach in a PKU mouse model (C57Bl/6-Pahenu2) was employed to examine its preclinical feasibility. A recombinant adeno-associated virus (rAAV) vector containing the murine Pah-cDNA was generated, pseudotyped with capsids from AAV serotype 8, and delivered into the liver of PKU mice via single intraportal or tail vein injections. The blood Phe concentrations decreased to normal levels (< or =100 microM or 1.7 mg/dl) 2 weeks after vector application, independent of the sex of the PKU animals and the route of application. In particular, the therapeutic long-term correction in females was also dramatic, which had previously been shown to be difficult to achieve. Therapeutic ranges of Phe were accompanied by the phenotypic reversion from brown to black hair. In treated mice, PAH enzyme activity in whole liver extracts reversed to normal and neither hepatic toxicity nor immunogenicity was observed. In contrast, a lentiviral vector expressing the murine Pah-cDNA, delivered via intraportal vein injection into PKU mice, did not result in therapeutic levels of blood Phe. This study demonstrates the complete correction of hyperphenylalaninemia in both males and females with a rAAV serotype 8 vector. More importantly, the feasibility of a single intravenous injection may pave the way to develop a clinical gene therapy procedure for PKU patients.

Cerebral glucose metabolism in adults with early treated classic phenylketonuria

Classic phenylketonuria (PKU) is characterized by severe mental retardation in untreated individuals and mild neurocognitive abnormalities in some early treated adults. The exact biochemical mechanisms underlying this neurotoxicity remain undetermined. Several theories implicate abnormal cerebral energy utilization and alterations in biochemical pathways that involve glucose metabolism. This pilot study was undertaken to investigate whether 18F-deoxyglucose positron emission tomography (PET) is an effective tool to study cerebral glucose metabolism in early treated PKU. After PET coregistration with SPGR MRI, relative glucose metabolic rates (rGMR) at the center of standard atlas positions was determined. Repeated measures MANOVA was used to assess regional metabolic differences, which were then correlated with age-specific and day-of-scan plasma phenylalanine and age. Patients with PKU in comparison to controls had decreased rGMR in cortical regions including the prefrontal, somatosensory, and visual cortices, and increased activity in subcortical regions including the striatum and limbic system. Day-of-scan phenylalanine correlated with abnormal activity in subcortical structures, and older age was associated with decreased activity in the prefrontal and visual cortices. The clinical significance of these abnormalities of glucose metabolism in specific areas of the brain remains unknown.

MR Spectroscopy of Metabolic Disorders

The application of MR spectroscopy (MRS) in pediatric brain disorders yields valued information on pathologic processes, such as ischemia, demyelination, gliosis, and neurodegeneration. Because these processes manifest in inborn errors of metabolism, the purposes of this article are to (1) describe the spectral changes that are associated with the relatively common metabolic disorders, with summaries of known spectroscopic features of these disorders; (2) offer suggestions for recognition and distinction of disorders; and (3) provide general guidelines for MRS implementation. Although many conditions have a similar presentation, MRS offers valuable information for the individual patient in diagnosis and therapy when integrated fully into the clinical setting.

Inter-individual variation in brain phenylalanine concentration in patients with PKU is not caused by genetic variation in the 4F2hc/LAT1 complex

It remains a question why some patients with phenylketonuria (PKU) have high IQ and low brain phenylalanine (Phe) concentrations in spite of high blood Phe levels. One possible explanation for the low brain Phe concentrations in these patients would be a reduced transport of Phe across the blood-brain barrier. The 4F2hc/LAT1 complex has been suggested to be the most important molecular component responsible for this transport. To test the hypothesis that structural variant(s) in the genes encoding 4F2hc and LAT1 might result in a complex with reduced affinity for Phe, we have screened the two genes for sequence variants in a group of 13 PKU patients with a low ratio of brain to blood Phe concentrations. Several common sequence variants were identified, but none of these is predicted to affect the resulting protein product. Our data suggest that individual vulnerability to Phe in patients with PKU is not due to structural variants in the 4F2hc/LAT1 complex.

Diffusion-weighted MR imaging in patients with phenylketonuria: relationship between serum phenylalanine levels and ADC values in cerebral white matter

PURPOSE

To prospectively determine the relationship between serum phenylalanine levels and apparent diffusion coefficient (ADC) values in the cerebral white matter of patients with phenylketonuria (PKU).

MATERIALS AND METHODS

Institutional review board approval was obtained, and participants provided informed consent. Magnetic resonance (MR) imaging, which included T1- and T2-weighted, fluid-attenuated inversion-recovery (FLAIR), and diffusion-weighted examinations, was performed in 21 patients with PKU (nine male and 12 female patients; age range, 3-44 years; mean age, 19.4 years). ADC values in deep cerebral white matter were calculated for each patient. Serum phenylalanine levels were obtained in all patients within 12 days after MR imaging. Serum phenylalanine levels were measured in 16 patients 1 year before MR imaging. ADC values in cerebral white matter and serum phenylalanine levels were compared. A total of 21 control subjects (12 male and nine female patients; age range, 3-33 years; mean age, 20.6 years) underwent MR imaging. ADC values in cerebral white matter were compared with serum phenylalanine levels by using the Pearson correlation.

RESULTS

Abnormal high signal intensity in white matter on T2-weighted and FLAIR MR images was noted in patients with PKU who had serum phenylalanine levels of more than 8.5 mg/dL (514.2 micromol/L). Diffusion in posterior deep cerebral white matter tended to be restricted in patients when increased serum phenylalanine levels were measured after MR imaging (r = -0.62). There was a correlation between ADC values in posterior cerebral white matter and serum phenylalanine levels measured 1 year before MR imaging (r = -0.77). ADCs of control subjects were significantly higher than ADCs of patients with PKU (P < .005).

CONCLUSION

Posterior deep white matter in patients with PKU and a serum phenylalanine level of more than 8.5 mg/dL showed high signal intensity in white matter on T2-weighted and FLAIR MR images and revealed decreased ADC. We suggest that to avoid brain-restricted diffusion due to hyperphenylalanemia, patients with PKU should maintain serum phenylalanine levels of less than 8.5 mg/dL (514.2 micromol/L).

Consensus national sur la prise en charge des enfants dépistés avec une hyperphénylalaninémie

Phenylketonuria (PKU) is an inherited metabolic disease affecting about one birth out of 15 000. From 1978, a national systematic neonatal screening was set up in France with a regional organisation. French rational and guidelines have been established by the national PKU group with the collaboration of all the physicians responsible for the regional centres. These guidelines specify the minimal diagnosis procedures leading to an optimal treatment of all patients. A low-phenylalanine diet must be started as soon as possible in the neonatal period for all newborns whose phenylalanine levels are above 10 mg/dl. The dietary control must keep the phenylalanine plasma levels between 2 and 5 mg/dl until 10 years of age. After this age, several data argue for a progressive and controlled relaxation of the diet, keeping the phenylalanine level below 15 mg/dl until the end of the adolescence and below 20 to 25 mg/dl in adulthood. All PKU patients must be followed up for life, in order to screen those who may not bear the diet relaxation and in order to strictly prevent maternal PKU deleterious consequences.

Treatment of Phenylketonuria-associated Tremor with Deep Brain Stimulation: Case Report

OBJECTIVE AND IMPORTANCE:

Phenylketonuria (PKU) is an inborn error of metabolism that causes severe neurological impairment, despite dietary treatment. We present a case of PKU-induced cerebellar tremor treated with deep brain stimulation. There have been no previously reported cases of a patient with a PKU tremor treated with deep brain stimulation.

CLINICAL PRESENTATION:

A 36-year-old male patient with PKU presented with signs of cerebellar disease including dysmetria, resting tremor, and intention tremor in the left upper extremity.

INTERVENTION:

A deep brain stimulation electrode was placed in the ventral intermediate nucleus of the right thalamus.

CONCLUSION:

Immediately after surgery, the patient had nearly complete resolution of intention tremor in the left arm. His resting tremor in the left hand was also greatly improved. The 30-month follow-up examination revealed maintenance of the immediate postoperative improvement.

Living with phenylketonuria: perspectives of patients and their families

This study surveyed PKU patients and their primary caretakers to assess their current management practices, the barriers to effective management, and the potential utility of a home monitor in managing PKU. A survey instrument was mailed to caretakers of all 50 patients with PKU in Utah between the ages of 2 and 18 years in 1997 (response rate 64%). It included separate components for caretakers and patients aged 10 to 18 years. Although there was uneven compliance with recommended practices, caretakers universally recognized the negative consequences of not adhering to the low-protein diet. There was, however, disagreement regarding such consequences among the older children surveyed. The primary obstacles cited to better adherence were time constraints and stress associated with food preparation and record-keeping, and the restrictions imposed on social life. Phenylalanine test results were regarded as the principal signal for the need for dietary adjustment. Despite the facts that obstacles to dietary adherence are multifaceted and that no single intervention would therefore serve as a panacea, a large majority of respondents believed a home monitor would facilitate better management of PKU through more regular and timely feedback.

Nutritional genomics

Nutritional genomics has tremendous potential to change the future of dietary guidelines and personal recommendations. Nutrigenetics will provide the basis for personalized dietary recommendations based on the individual's genetic make up. This approach has been used for decades for certain monogenic diseases; however, the challenge is to implement a similar concept for common multifactorial disorders and to develop tools to detect genetic predisposition and to prevent common disorders decades before their manifestation. The preliminary results involving gene-diet interactions for cardiovascular diseases and cancer are promising, but mostly inconclusive. Success in this area will require the integration of different disciplines and investigators working on large population studies designed to adequately investigate gene-environment interactions. Despite the current difficulties, preliminary evidence strongly suggests that the concept should work and that we will be able to harness the information contained in our genomes to achieve successful aging using behavioral changes; nutrition will be the cornerstone of this endeavor.

Adult phenylketonuria

Newborn screening for phenylketonuria began 35 to 40 years ago in most industrialized countries. Because of this initiative, which resulted in early institution of phenylalanine-restricted diets, there are now many young adults with this disease who have normal or near-normal intellectual function. In North America alone, 200 patients with phenylketonuria enter adulthood every year. Most expert panels recommend following a phenylalanine-restricted "diet for life." However, there are few adult physicians dedicated to continuing care of this group, with the possible exception of maternal phenylketonuria. Up to 10% of adults with classic phenylketonuria, and possibly 50% of those with milder variants, may not need treatment; after adolescence, intelligence does not appear to deteriorate, at least into early adulthood, even if diet therapy is discontinued or not in good control. However, neuropsychological and psychosocial problems develop frequently, needing focused and intensive support by health care providers. New investigative methods and treatment options are on the horizon. There is an urgent need for physicians who will orchestrate the care of adults with phenylketonuria.

The call from the newborn screening laboratory: frustration in the afternoon

Newborn screening programs in the United States are evolving in concert with technologic advances in analytic chemistry and medicine. Many more disorders are being identified on dried filter paper blood spots without fundamentally altering the basic principles first put forward in the 1960s. Some disorders have been added without researchers knowing if there is a true benefit to early diagnosis and treatment; some disorders currently being detected will merit little or no follow-up in the future. The general principles underlying newborn screening are discussed, as are the individual disorders screened in most programs. The expanding and evolving impact of tandem mass spectrometry on newborn screening is also explored.

Neuropsychological outcome of subjects participating in the PKU adult collaborative study: a preliminary review

Adult subjects with classical phenylketonuria (PKU) who were diagnosed and treated neonatally participated in this long-term follow-up study. Twenty-four subjects received neuropsychological (NP) assessment and a subset received magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) to identify: (1) pattern of cognitive dysfunction; (2) effect of high blood phenylalanine (Phe) level at time of cognitive testing; and (3) treatment variables that may be associated with cognitive difficulties in adulthood. All subjects had average IQ except one subject in the borderline range. Diet was initiated by the 15th day of life. All subjects except one were on diet until age 6 years (mean years of treatment = 15). Blood Phe levels at cognitive testing ranged from 157 to 1713 micromol/L (mean = 1038); 11 subjects had levels < 1000 micromol/L and 13 subjects had levels >1000 micromol/L. Results suggest that adults with early-treated PKU demonstrate specific cognitive deficits, a number of which are associated with the frontal and temporal area of the brain. Deficits were noted in several domains including executive functioning, attention, verbal memory, expressive naming and verbal fluency. Self-report measures of depression and anxiety were generally in the normal/mild range. The group with a Phe level > 1000 micromol/L scored lower than the group with Phe level < 1000 micromol/L on measures of focused attention, verbal fluency, reaction time, verbal recognition memory, visual memory and naming. Tests of cognitive functioning were often correlated with measures of treatment during childhood rather than with Phe level at the time of cognitive testing. Subjects with abnormal MRI scored significantly lower on two cognitive tests (Trails A and CVLT Recognition Memory). We found no significant correlation between current brain Phe level obtained through MRS (n = 10) and neuropsychological functioning. Future longitudinal investigation with a larger sample size will assist in clarifying the aetiology of neuropsychological deficits and association with treatment history.

Dietary interventions for phenylketonuria

BACKGROUND

Phenylketonuria is an inherited disease for which the main treatment is the dietary restriction of the amino acid phenylalanine. The diet has to be initiated in the neonatal period to prevent or reduce mental handicap however the diet is very restrictive and unpalatable and can be difficult to follow. Whether the diet can be relaxed or discontinued during adolescence or should be continued for life remains a contraversial issue which we aim to address in this review.

OBJECTIVES

To assess the effects of a phenylalanine restricted diet commenced early in life for patients with phenylketonuria. To assess the possible adverse effects of relaxation or termination of the diet on intelligence, neuropsychological outcomes and mortality, and to assess the effect on growth, nutritional status and eating behaviour and quality of life.

SEARCH STRATEGY

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Trials Register which is a specialist trials register which comprises references identified from comprehensive electronic database searches, handsearching relevant journals and handsearching abstract books of conference proceedings. Additional studies were identified from handsearching the Journal of Inherited Metabolic Disease (from inception, 1978 to 1998). The manufacturers of dietary products for phenylketonuria were also contacted. Date of the most recent search of the Group's specialised register: November 1999.

SELECTION CRITERIA

All randomised or pseudorandomised controlled trials comparing a phenylalanine restricted diet to either relaxation or termination of dietary restrictions in patients with phenylketonuria.

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed the trial eligibility, methodological quality and extracted the data.

MAIN RESULTS

Four studies were included in this review including a total of 251 patients. Few statistically significant differences were found between treatment and comparison groups for any of the outcomes apart from for blood phenylalanine level and intelligence quotient. Blood phenylalanine levels were significantly lower in those subjects with phenylketonuria following a phenylalanine restricted diet compared to those on a less restricted or relaxed diet (weighted mean difference at three months -672.203, 95% Confidence interval (CI) -813.799 to - 530.608). Intelligence quotient was significantly higher in subjects who continued on the phenylalanine restricted diet compared to those who terminated the diet (weighted mean difference after 12 months -5.00, 95% CI -9.595 to -0.405). However this is based on the results of only one study.

REVIEWER'S CONCLUSIONS

The results of non-randomised studies have concluded that a phenylalanine restricted diet is effective in reducing blood phenylalanine levels and improving intelligence quotient and neuropsychological outcome. No randomised controlled trials have assessed the effect of a phenylalanine restricted diet versus no dietary restrictions from diagnosis. In view of evidence from non-randomised studies, such a trial would now be unethical and it is recommended that phenylalanine restricted diet should be commenced at the time of diagnosis. There is uncertainty about the precise level of phenylalanine restriction and when, if ever, the diet should be relaxed. These questions should be addressed by randomised controlled trials with careful consideration given to which patients to include.